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The A Axis usually refers to the fourth axis of a CNC machine and is usually a rotational axis. The fourth axis sits underneath a typical X,Y,Z setup. Picture a stepper or servo controlled lathe on the table of a typical 3 axis machine. That is your 4th axis. It is important to understand the…continue reading
The ABEC scale is an industry accepted standard for the tolerances of a ball bearing. It was developed by the Annular Bearing Engineering Committee (ABEC) and hence the name. The scale is designed to allow a user to make an informed decision about the type of bearing they are purchasing. As a point of reference…continue reading
In Geometry there are three axis’ of movement (X, Y, Z). It is therefore confusing at first to hear of a 5 or 6 axis CNC machine. How can there be more than 3 axis’? In CNC terminology an axis is either a linear or rotary freedom of movement.
A CNC machining center dedicated to grinding tools and inserts.
A device that enables CNC machines to store and change tools while maintaining accurate and repeateable Z heights.
ASE is a CAD file extension for the software program Autodesk’s 3DS Max CAD programwhen exporting ASCII files (i.e. drawing.ase). Examples of other common CAD file extensions include *.dxf, *.3ds, *.stl.
An arbor (American English) is synonymous with the term mandrel (also spelled mandril). An arbor can be either a workholding device or a toolholder. For example you may read in a catalog, drill chuck (includes R8 arbor). The arbor here refers to the portion that adapts the spindle of your mill to the actual drill…continue reading
Annealing is the process of heating a material (in most cases steel) with the purpose of altering its properties namely, strength and hardness. Annealing is used to induce ductility (the amount a material can be deformed without fracture), soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.…continue reading
Angular contact bearings are ball bearings designed to deal with axial loads (the bearings on a merry-go-round are good examples of bearings with high axial loads). A typical ball bearing is designed to deal with pure radial loads (i.e. skateboard bearings) and are not well supported in the axial direction. They are commonly used to…continue reading
The term active-high refers to a high voltage signal that represents the binary digit 1. For example, in a 5 volt system designed to be “active high” the binary “1″ would be represented by a voltage close to 5 volts. The opposite would be true for an active-low system. The term active-low refers to a…continue reading
Technically, Acetal is a molecule with two single bonded oxygens attached to the same carbon atom. In the world of CNC an acetal plus teflon combination makes an excellent low friction material with which to coat machine ways or even create linear bearings. This method is inferior to linear bearings in terms of efficiency and…continue reading
Accuracy refers to how close an actual measurement is to its true value. For example, a hardened rod is very accurate if it is supposed to be .0001 and it is in fact .0001. That is high accuracy. Precision on the other hand refers to the repetability of a measurement no matter how accurate it…continue reading
Absolute coordinates are expressed relative to a fixed position (in most cases the homing switches of your machine). Relative coordinates on the other hand are relative to the current position of the cutting tool (think zeroing your tool at some arbitrary point on the table). Helpful Gcodes in this regard are the following: * G90…continue reading
Brushless DC Motor A brushless DC motor is identical to a brushed DC motor but does not require brushes as the name implies. Brushes in a convential DC motor are used to switch the electrical current from positive to negative every 180 degrees (a non-negotible feature if we want the motor to actually turn). The…continue reading
A bridge rectifier which is synonymous with a full wave rectifier is an electrical configuration of four diodes (arranged in a bridge) to convert AC current (the kind coming out of your wall) to DC current (the kind coming out of a battery). In the diagram below the left image shows AC current as seen…continue reading
Breakout Board A breakout board is an extremely useful device to take a cable (for example an DB25 printer cable) and breakout all 25 pins to individual headers for the purpose of point to point wiring. If boards like this were not commercially available, our only option would be to hand strip all 25 of…continue reading
The guys over at cnccookbook.com offer this excellent drawing to show the distinction between box ways and dovetail ways. Both methods of sliding the table are metal on metal (lubricated with oil). These are typically found in knee type mills and larger industrial metal working equipment. Box Ways vs Dovetail Ways… A third class…continue reading
A bounding box is used in CAD drawing to get a rough estimate of how much volume a 3D object contains. A bounding box is defined as the smallest box that can be drawn and still contain the object(s) you are “bounding.” So in the picture below the bounding box cube has been roughly drawn…continue reading
A machine control that provides the option of skipping a predetermined series of program blocks. Basically any time the control software sees a line of code that starts with a forward slash “/” it will skip it. If you are familiar with programming languages, it is the same things as commenting out a line. …continue reading
The basic unit of the nc (short for cnc) program is the block. Blocks of code set settings or perform functions. A permissible block of input is currently restricted to a maximum of 256 characters. The following order is required for the construction of a block. an optional block delete character, which is a slash…continue reading
Stepper motors come in two main flavors: bipolar and unipolar. A unipolar motor can be run in bipolar mode but a bipolar motor cannot be run in unipolar. This is because a bipolar motor does not have a center tap. Unipolar motors are usually wired Figure 1.2 Images in this article courtesey of Jones on…continue reading
Belt drives are used in CNC machines for mating a motor with a spindle or ballscrew/leadscrew. Belts are chosen over couplers for a couple of different reasons. Gearing is possible when using belts and so it is therefore possible to increase or decrease the resolution based on belt pulley size selection. It is also possible…continue reading
Bellows are rubber or paper pleats folded in an accordian like fashion and used to protect the ways and leadscrews on a machine from chips and coolant. If bellows are to be used on a machine it is critical that they be designed into the machine from the start! Otherwise significant loss of travel will…continue reading
A bed mill is a style of mill where the bed is fixed and the Z axis is adjusted by the entire head sliding up and down a verticle column on ways. This is in contrast to a knee-type mill where the bed slides up and down the base on vertical ways. Compare the two…continue reading
The B-Axis is the rotational axis along the X-Axis. This is traditionally performed by rotating the cutting tool (as opposed to a lathe style rotation like in the A-axis). Below is an example of a B Axis cutting head:
Bar Feeders and Pullers are devices used to automate a continuous feed of bar stock to a lathe so that the operator doesn’t have to keep loading new stock as parts are made. Here is an example fo what one looks like:
Ballscrew Mapping is a software feature of CNC control software (i.e. Mach 3) that maps the errors of a ball screw axis and automatically compensates form them. Any screw wears unevenly due to the fact that certain parts of the table (i.e., the middle) are used far more than other parts of the table (the…continue reading
Quite simply a ball screw is a glorified threaded rod. All screws are mechanical devices for translating rotational motion to linear motion. A ballscrew manages to do this with very little friction and little to no backlash. It accomplishes this via a precision threaded shaft which provides a spiral raceway for ball bearings to…continue reading
The ball nut is to a ballscrew what a nut is to a bolt. The nut simply travels along the screw translating the rotary motion into linear. Below is a diagram indicating the various parts of a ball nut:
Ball end mills are end mills that have a half spherical bottom (examples pictured below). They’re typically employed in 3D profiling (as opposed to profiling or pocketing. For example, carving out a 3D chess piece) because they don’t have a flat bottom and hence tend to smooth out the steps. They have some unique cutting…continue reading
Backplotting is a CAM software feature where the G-Code is interpreted graphically on the screen to analyze. This graphical representation of G-Code enables programmers to spot and correct problems before running the G-Code files.
A device used to take up the backlash in a leadscrew and enable climb milling. This could be as simple as a pair of preassure loaded nuts as in this photo: Or as complicated as the picture below: In either case, this is a problem unique to leadscrews since ballscrews are designed to be zero…continue reading
Backlash compensation is a software feature designed to reduce the effects of backlash in a system. When an axis is reveres there is a certain amount of “slop” in the system that needs to be taken up before actual movement begins. If the software knows how much slop exists the backlash compensation feature can automatically…continue reading
Backlash is any kind of undesirable movement in an axis due to mechanical sloppiness. It is most easily illustrated by moving an axis one direction, taking a measurement and then slowly reversing the direction of movement until the slop is taken up. This “dead zone” is called backlash. A sloppy steering wheel in an old…continue reading
Back Driving is the tendency a ballscrew can have to spin when an axial force is applied to the nut. If you were to replace the leadscrew in your car’s sissor jack with a ballscrew you would have a serious backdriving problem. The weight of the car would “drive back” the jack to its starting…continue reading
When a step motor or servo motor is decelerated, it generates “Back EMF
The button control used to execute the G-code in the control software. This control can be used to begin a program or resume a program that has been paused. The control can either be a software button (something you clikc with a mouse or hotkey) or a hardware button on the panel that links to…continue reading
Cycle Stop is the control in the CNC panel that halts the execution of G-Code. Again this can be a software or hardware interface.
Cutting force refers to the force exerted on the workpiece by the tool. High cutting forces can potentially cause deflection, inaccuracy, chatter, and broken tooling. Cutting force increases with cut depth, material hardness, and friction coefficient. Cutting forces are inversely propoortional to rake angle. Power required increases with the feed rate.
Cutter radius compensation allows a program to be written without considering the size of the cutter being used. Three G codes are used to control compensation G40, G41 and G42. They are group modal. G40 cutter compensation off, centre line programming. G41 cutter compensation to the left of the programmed path. G42 cutter compensation to…continue reading
Cutter offset is the distance from the surface of part to bottom of tool along the z axis. In practice cutter offset is a predetermined distance from the surface of the workpiece that allows for the safe and rapid movement of the cutting tool between cutting operations.
A crash is the unfortunate condition of “crashing” your tooling into a limit switch, workholding or some other unintended obstacle. The result is often either broken tooling or broken machines. There are several methods of avoiding costly crashes: Perfrom dry runs Use simulation software On untested parts files cut s-l-o-w-l-y Setup soft limits Crashes can…continue reading
A counterweight is a force used to counter the effects of gravity on the Z axis. When the mass of the Z axis is significant one needs to use either very large motors to move and position the axis or construct a counterweight system so that the axis is more neutral. This can sometimes be…continue reading
A counterbore (sometimes referred to as countersink) is a common machine operation to recess the head of a bolt into the surface of material. Pictured below is a specialized counterbore tool. It is possible to drill a hole and create a counterbole with a standard endmill but the specialized tool does it in one step…continue reading
In standard G-code a coordinate word is a section of code that begins with an axis letter followed by a position. For example, Y2.0175 is a coordinate word that may be part of a larger block of code.
Coordinate rotation is a method of allowing the controller software to automatically compensate for parts that are not perfectly squared into their fixtures. For example, imagine a simple part with 2 cored holes that are used for reference points. The left hole is the zero-point and the right hole is 12″ away along the ‘X…continue reading
As the name implies, coolant in the form of liquid, air or mist “cools” the cutting tool and provides lubrication as well as assists in removing chips. Proper use of coolant can prolong tool life, allow higher cutting speeds, and improve surface finishes. Most flood coolant systems have a recirculating pump to recycle the coolant…continue reading
Conversational CNC is a type of G-Code programming. There are actually three types of programming methods, manual programming , conversational programming (which is also called shop floor programming), and computer aided manufacturing (CAM) system programming. Each has it’s place and application. Conversational CNC can most easily be thought of as a G-code “wizard.” For example,…continue reading
A milling cutter can cut in two directions: Conventional and Climb. Conventional milling moves the cutting tool opposite the direction it wants to travel. The chip thickness starts at zero thickness, and increases up to the maximum. The cut is so light at the beginning that the tool does not cut, but slides across the…continue reading
Contour Turning is an operation performed on a lathe that feeds a tool along a curved line in order to create curved, cylindrical shapes. It is analagous to contouring on the mill and is sometimes called profiling.
Contouring is very simply the process of cutting smooth a smooth continuous curve or surface in CNC. Countouring by definition is impossible to do with manual mills and lathes since it requires the simultaneous movement of two or more axis to perform the operation (a task that even the most skilled among us would fail…continue reading
A contactor is a heavy duty relay capable of carrying high currents such as those used by motors. The term contactor comes from the way these relays work. There are heavy guage plates of copper that toggle back and forth via an electromagnet “contacting” copper posts and allow current to flow. In a CNC machine,…continue reading
The best way to explain this is to quote exactly from Mach 3′s white paper on this subject: Constant Velocity “CV
Constant surface speed as applied to lathes is the technique of automatically varying the spindle speed as the tool moves along a contour. The goal of this technique is to maintain a constant speed as the cutter moves over the workpiece. Large diameter portions of the part much turn much slower than smaller diameter portions…continue reading
Combination lathe can refer to one of three things: A lathe with a tailstock. As opposed to a “chucker” which is a lathe without a tail stock. A lathe that may be run as CNC or manual. A lathe that has milling and drilling features “combined” into one machine (3-in-1 machine as pictured above).
A collet is a mechanical device used to hold a tool or workpiece. Some of the more popular collet standards include: 5C Collets (Invented by Hardinge, commonly used with lathes) ER Collets (DIN 6499) R-8 (The Bridgeport standard) 16C 3C MT (Morse taper 0-7; DIN 228-1) 3J WW The collet works by squeezing…continue reading
Cogging or cogging torque (also known as detent or ‘no-current’ torque) is the “jerky” rotation of the shaft (uneven torque through a roation) due to the interaction of the permenant magents of the rotor and the stator. (Even though the term cogging is used to describe DC motors, the “feel” is analgous to rotating a…continue reading
A closed loop system is a motion control system that has a feedback loop (usually an encoder) to determine if commands are properly executed. Here is how a feedback loop typically works: Driver sends motor command to move X amount in Y direction Driver delivers voltage required to execute command. Encoder on motor monitors position…continue reading
A milling cutter can cut in two directions: Conventional and Climb. Conventional milling moves the cutting tool opposite the direction it wants to travel. The chip thickness starts at zero thickness, and increases up to the maximum. The cut is so light at the beginning that the tool does not cut, but slides across the…continue reading
Circular Interpolation is combining the movement of two linear axis’ into a smooth arced or circular motion. Since an axis can only move linearly, intellegent coordination of axis’ are required to create an arc. G02 causes the motion to be in a clockwise direction, while G03 is counter-clockwise. Circular interpolation requires an endpoint, a feed…continue reading
A chucker lathe is identified as one that does not have a tailstock. Another term sometimes used to describe a chucker lathe is an automatic turret lathe. Small- to medium-sized automatic turret lathes are usually called “screw machines” or “automatic screw machines”, while larger ones are usually called “automatic chucking lathes”, “automatic chuckers”, or “chuckers“.
A chuck is a specially designed clamp to hold the rotating workpiece in a lathe. Self-centering chuck uses dogs (usually called jaws), interconnected via a scroll gear (scroll plate), to hold onto a tool or workpiece. Because they most often have three jaws, the term three-jaw chuck without other qualification is understood by machinists to…continue reading
Chip load is the thickness of a chip measured in thousandths (i.e.: 0.010) per tooth that is removed by one cutting edge of the tool (Chip load is also sometimes measured as feed per tooth). Chip load is an important factor in tool life because it determines how much heat will be carried away from…continue reading
A chip breaker is a small groove ground on the back of the cutting edge on a lathe tool or insert to keep the chips short. The chip breaker causes the chip to curl until it breaks off.
A chip auger is basically a long rotating shaft with a helical blade that removes chips from a machining center. Usually they are loaded into a hopper or placed onto a conveyer belt.
As the name implies, a chip conveyer is a moveable belt that helps to carry away the incredible amount of chips that are generated from machining centers.
Chatter refers to vibration or sound that comes from the machine tool under certain conditions. It interferes with proper cutting and produces cutting errors and bad surface finish. Generally, it is a harmonic vibration or natural resonance. It can be triggered through improper setup or operation of the machine. Frequently, changing the spindle speed, depth…continue reading
A charge pump or safety charge pump is a electrical hardware device that functions as a safety switch between the software and the CNC machine. The charge pump will only allow the CNC machine to function if the software is ready. This charge pump essentially turns off the machine until the software had indicated that…continue reading
A chamfer is a beveled edge connecting two surfaces. In common terms chamfering is simple rounding an edge. This operation is performed for reasons of appearance and feel, or to avoid weakness for stress (i.e. a telescopic mirror). Special chamfering bits are sometimes used to apply this finished touch to rough edges. A fillet on…continue reading
Centerline programming refers to CNC Gcode written in such a way that the toolpath is programmed along the centerline of the mill cutter (or the virtual tip in turning). Since it is rare that we actually want to cut this way, the actual path is generated using the centerline as a reference and calculating the…continue reading
A center cutting end mill is distinguished from a non center cutting end mill in that it has the ability to plunge the end mill in much the same way one would plunge a drill bit. End mills with coolant passages down the center of the bit are not centercutting and consequently cannot plunge straight…continue reading
The C Axis is the rotational axis around the Z axis. In and of itself a machine with just C Axis capability would be pretty useless. But if you couple it with B Axis movement you have a 5 axis machine with incredible versatility. Below is one such example. Here is diagram that may…continue reading
Most commercial CNC machines in the USA use a CAT taper which is a modified NST 30, 40, or 50 taper that uses a pull stud and a groove in the flange. The machine pulls on the pull stud to hold the holder in the spindle, and the groove in the flange gives the automatic…continue reading
Machining with carbide can be difficult, as carbide is more brittle than other tool materials, making it susceptible to chipping and breaking. To offset this, many manufacturers sell carbide inserts and matching insert holders. With this setup, the small carbide insert is held in place by a larger tool made of a less brittle material…continue reading
Carbide is an extremely hard compound (more specifically the compound tungsten carbide or titanium carbide) used as a cutting surface in machine tools. It is valuable because it resists wear, heat, and is extremely rigid. A good carbide tip might hold an edge ten to twenty times longer than a tool steel tip. The entire…continue reading
A capacitor is an electronic component that functions much like a battery in that it stores up charge and will release it when called to. Think of it as a reservoir for smoothing fluctuations in electrical currents or a ballast to help resist wave spikes. Electrolytic capacitors have particularly large capacities and are used in…continue reading
A canned cycle is a sequence of machine operations initiated by a single G code. Canned cycles act as shortcuts that simplify the program. One could describe a certain operation entirely with G0 and G1 commands but a canned cycle is a single line of code which, in effect, says “Start cutting here, finish cutting…continue reading
CAM software (Computer Aided Manufacturing) is the software that sits in between the controller software and the CAD software. The job of the CAM software is to ask the operator a few key questions like, size of material, type of tool being used, starting point, feedrate, depth of cut, etc and then using that data…continue reading
CAD software (Computer Aided Drawing) is basically drawing software to construct a model in either 2D or 3D. There are many, many quality packages out there. Here are a list of only a few of the available packages.
Center drilling is a process in which a specially designed rigid drill precisely locates a hole in the center of a workpiece. The purpose of center drilling is to establish a true centerline diameter. Without center drilling there is the inevitable tendency for drills to run out and wander. Stub drills can increase precision without…continue reading
DB25 is shorthand for a 25pin connector common in computer applications. This type of connector is typically used in conjunction with what has been traditionally called the “printer port” although this has been largely superceded in recent days by the USB port. The DB25 connector and its associated printer port (i.e. LPT1) are important for…continue reading
DXF (Drawing Interchange Format, or Drawing Exchange Format) is a CAD data file format (i.e. mycaddrawing.dxf) developed by Autodesk for enabling data interoperability between AutoCAD and other programs. HEADER section – General information about the drawing. Each parameter has a variable name and an associated value. CLASSES section – Holds the information for application-defined classes…continue reading
DWG (“drawing”) is a file format used for storing two and three dimensional design data and metadata. It is the native format for several CAD packages including AutoCAD, IntelliCAD (and its variants) and Caddie. In addition, DWG is supported non-natively[2] by many other CAD applications. The .bak (drawing backup), .dws (drawing standards), .dwt (drawing template)…continue reading
The dwell command is used to cause axis motion to pause for a specified period. G04 is the G-Code command to force a dwell between operations. Also, any point in a toolpath where the cutter stops, perhaps just prior to changing direction or before retracting. A dwell can often introduce visible marks in the…continue reading
Duplex or paired bearings are two similar bearings of same type (i.e. the bearings could be deep grove, angular or taper roller bearings) arranged next to one another to provide preload. Duplex bearings can also be mounted with the provision of a small spacer in between them. This is done in some cases to increase…continue reading
Dry machining is simply machining without coolant. Since heat is the number one enemy of sharp toolilng, sometimes compressed air is used to coolthings down. Dry machining or near dry machining is becomeing increasingly poplular due to governmental regulations imposed upon machine shops in disposing of used coolant. Dry machining may not even reduce the…continue reading
DRO (Digital Read Out) provides a digital (as opposed to analog) display of the location of a particular axis. This digital display can either be displayed on a computer screen as an output of control software (ie. Mach 3) or through a dedicated display device and actual linear scales or encoders.
A drive in CNC usually refers to either a servo drive or a stepper drive. This is the electrical device that “drives” the stepper or servo motor. Since stepper and servo motors use radically different technology, stepper drives are not compatible with servo drives. However, the input signals these drives receive, in some cases, can…continue reading
Drip Feed a method of feeding the control software managable portions of G-Code in the event that the program file exceeds the available memory in a computer. DNC software is designed to network and manage this dripfeed process. As memory becomes less expensive and machines more powerful, drip feeding becomes less necessary.
A steel wedge used to remove tapered shank tools from spindles, sockets, and sleeves. This tool might take the place of unscrewing a drawbar and “tapping” on it to release the tapered shank from the spindle. The drill drift takes the place of the tapping action.
A drill bushing is a hardened steel cyclider drilled hole matched to a specific drill bit. They are designed to prevent the drill bit from wandering and drifting when attempting to drill precision holes. The diagram above shows how such drill bushing is used in conjunction with a jig.
Drawbars are used on milling machines to pull collets and toolholders into their corresponding tapers. The drawbar may be threaded into the collet, or they may grip the toolholder’s retention stud.
Dovetail ways are metal on metal sliding linear ways. They resemble dovetail grooves that woodworkers use to make boxes. These are to be contrasted to box ways which are cut at 90 degree angles to each other. A third class of ways are called linear bearings which use recirculating ball bearings to do the trick. …continue reading
A dongle or usb key is a small piece of hardware that connects to a computer. It looks close very similar to a USB flash drive. It’s purpose is to authenticate a piece of software. The software will not run without this peice of hardware. In recent years, the word dongle has adapted further meanings. …continue reading
Depth of Cut is how deep the tool is under the surface of the material being cut. The depth of cut will determine the height of the chip produced. Typically, the depth of cut will be less than or equal to the diameter of the cutting tool. It takes more power to run a higher…continue reading
DNC is a CNC controller protocall used to link CNC machines together on the machine floor. A DNC controller. In cases where the program file exceeds the available memory of the CNC machine, DNC is used to dripfeed the program to the controller one block at a time. If the DNC controller is connected to…continue reading
DIN 66025 / ISO 6983 is the main standardized version of Gcode in Europe. In the United States the Electronic Industries Alliance finalized RS274D as the accepted standard.
A digitizer (could be a mechanical tool probe or even laser scanner) is a device which maps the surface of a physical object in three dimensions and imports that model information into an appropriately equipped CAD/CAM software package.
A Digital Differential Analyzer (DDA), also sometimes called a Digital Integrating Computer referrs to the mathematical algorithm used to convert the right angle linear motion of CNC machines into smooth curves. Since a true curve is impossible in CNC everything is an approximation (albeit a very, very close approximation). This approximation a function of the…continue reading
Detent torque is the torque required to overcome the tendency of stepper motors to gravitate toward the magnetic poles. Detent torque can easily be felt as the shaft is rotated without power.
Delrin® is a thermoplastic acetal resin. The most important attributes of Delrin® are high mechanical strength and rigidity, fatigue endurance and high resistance to moisture, gasoline and solvents. It is often times used for linear bearings becasue of its low coefficient of friction and for leadscrews because of its tendency to expand and eliminate backlash.
Deflection is a term that is used to describe the degree to which a structural element is displaced under a load. In machining deflection could refer to a tool, workpiece, table or any other component where force is being applied. Typically deflection is undesirable since it means a loss of precision and accuracy.
A datum (plural datums, not data) is a reference point or surface from which measurements are made. It is the known starting point from which other points in a model are referenced.
The best way to explain this is to quote exactly from Mach 3′s white paper on this subject: Constant Velocity “CV
Exact Stop Check is initiated by a G-Code G09. The Exact Stop Check command is similar to Exact Stop Mode in that it attempts to follow the Gcode path “exactly” at whatever the cost to speed. The difference between Exact Stop Check and Exact Stop Mode is that Exact Stop Check turns this mode on…continue reading
An e-stop or emergency stop is the control that stops all machine operation in the event of a crash, runaway machine, or some dangerous or potentially dangerous situation. True emergency stop devices cut power to spindles, drives and any other powered element of a machine so that all sources of potential danger can be eliminated…continue reading
An endmill is a type of cutting tool used in industrial milling applications. It is distinguished from the drill bit, in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, a milling bit can generally cut in all directions, though some cannot cut axially. Endmills are used in…continue reading
A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position of a shaft or axle to an analog or digital code. Encoders are essential to closed loop systems (i.e. servo motors) because they provide the necessary feedback so that a motor can move to exact positions. To oversimplify…continue reading
A wiggler, edge-finder, or center-finder is a tool used in the spindle of a milling or drilling machine. The device is used to accurately determine edges or markings and therefore the center of a workpiece or a previously machined feature. Both mechanical and electronic edge-finders are used widely.
In Follow turning two tools and two independent tool turrets are used on a CNC lathe to speed cutting so that twice as much material is removed in a single pass. It is typically performed when roughing. The first turret leads and removes a standard depth of cut. The second turret follows the first…continue reading
Follow error is a term used in servo motor control systems and refers to the difference between where the axis is in the real world and where it should be based on what the CNC control program has commanded. Since acceleration cannot be infinite, it isn’t practical to insist on 0 following error at all…continue reading
A fly cutter is typically a single point cutter (only one cutting edge) used to mill large flat surface finishes in minimal passes. It is not uncommon to have a two in cutting path to finish a surface. Because the cutting edge is only removing material half of the time, fly cutters cut with a…continue reading
The term flute refers to the groove on the periphery of a cutter that allows for chip flow away from the cut.
Flood coolant is a high volume application of coolant usually applied through flexible tubing aimed at the cutting area. It’s purpose is to keep the tooling cool and carry away chips.
A fixture is a workholding or support device used in machining and is used to locate and in some cases hold a workpiece during either a machining operation or some other industrial process. A jig differs from a fixture in that it guides the tool to its correct position in addition to locating and supporting…continue reading
A finishing pass is usually the last pass over a part characterized by higher spindle speeds and a shallower depth of cut in order to improve the finish of a part and increase tolerances.
Fine in-position is another term for exact stop mode: The best way to explain this is to compare costant velocity mode with exact stop mode by quoting exactly from Mach 3′s white paper on this subject: Constant Velocity “CV
A ferrite bead is a passive electric component used to suppress high frequency noise in electronic circuits. Ferrite beads are one of the simplest and least expensive types of interference filters to install on preexisting electronic cabling. For a simple ferrite ring, the wire is simply wrapped around the core through the center typically 5…continue reading
The phrase speeds and feeds (or feeds and speeds) refers to two separate velocities in machining, namely, rotational cutting speed of the tool and feed rate. They are often considered as a pair because of their combined effect on the cutting process.
Feedrate override is a control in the CNC control software that adjusts the programmed feed rate by a designated percentage during operation. The feedrate override can adjust the machine to travel faster than the programmed rate or slower. There is often a limit to how much this can be adjusted to prevent crashing.
Feed hold is a CNC machine panel control that stops the machine from executing further commands. It is essentially the “pause” button for CNC control software. Feed hold pauses tool feed but does not stop spindle movement.
A program code that determines the feed during a cutting operation. For example the following code would move the machine to the Z height of 5 while cutting at a feedrate of 20 units per minute (units are being defined by a setting in the control software): G01 Z5.0 F20
A face mill is a type of mill cutter that contains multiple cutting teeth and is often used to remove large amounts of material. In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface. The milled surface results from the action of cutting edges located…continue reading
Many G codes and M codes cause the machine to change from one mode to another, and the mode stays active until some other command changes it implicitly or explicitly . Such commands are called “modal“. Modal codes are like a light switch. Flip it on and the lamp stays lit until someone turns it…continue reading
Gibs are essentially spacers used to compensate for wear along the linear ways of mills and lathes. All milling machines employ precision slide ways. The saddle, table, and the knee all ride along a box slide way or dovetail slide way. After time the parts that ride along the slide ways begin to wear. To…continue reading
Geometric dimensioning and tolerancing (GD&T) is a symbolic language used on engineering drawings and computer generated three-dimensional solid models for explicitly describing nominal geometry and its allowable variation. Some of the advantages of using GD&T include: It provides a clear and concise technique for defining a reference coordinate system and datums on a component or…continue reading
A popular manufacturer of inexpensive, quality servo and stepper motor drivers. The support and community surrounding this company is significant. Geckodrive has a Yahoo Group called ‘Geckodrive’. Go to http://groups.yahoo.com/. You will need to join the group to access the Files section and to post.
Gear drives involve the use of gears (as opposed to pulleys, timing belts or direct drive) to turn leadscrews, ballscrews or spindles. They’re less common for driving ballscrews and leadscrews because they typically involve backlash. They’re convenient for spindles because a transmission can be incorporated to change adjust the speed and power variables.
The generic term for the program that controls a CNC machine. Here is an example of a Gcode program broken into its individual parts: Line Code Description N01 M216 Turn on load monitor N02 G00 X20 Z20 Rapid move away from the part, to ensure the starting position of the tool N03 G50 S2000 Set…continue reading
A gas spring (aka gas strut) may be used as a counterweight on a Z-Axis to offset the effects of gravity and provide a more “neutral” state that does not require extreme holding torque. A counterweight is a force used to counter the effects of gravity on the Z axis. When the mass of the…continue reading
Gantry mills or routers refer to a router design in which two verticle members form meet a horizontal member to form a “bridge” which holds the Y-Z Axis actuator. This type of configuration (pictured) is very common upon plasma cutters and routers. It is less common among steel machines.
Gang Tooling is a method of mounting multiple tools on the crosslide of a CNC lathe so that they can be quickly moved into place thereby avoiding time costly tool changes. Pictured is an example of a crosslide with multiple tools ready for use.
A hybrid motor is a blend between the design of a permanent magnet stepper motor and a variable reluctance stepper motor. Permanent magnet motors use a permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor PM and the stator electromagnets. Variable reluctance (VR) motors have a plain iron…continue reading
High speed steel (often abbreviated HSS, sometimes HS) is a material usually used in the manufacture of machine tool bits and other cutters. It is superior to the older high carbon steel tools used extensively through the 1940s in that it can withstand higher temperatures without losing its temper (hardness). This property allows HSS to…continue reading
A home switch is usually some sort of sensor installed on an axis of a CNC machine to reference the machine. Both servo motors and stepper motors need to be referenced since they share a similar problem, namely, they do not know where they are on the table. Moving an axis into a homing switch…continue reading
Holding torque quite simply is the amount of torque required to hold the motor in position without moving. Sometimes called static torque, holding torque specifies the maximum external torque that can be applied to a stopped, energized motor without causing the rotor to rotate. Generally used as a figure of merit when comparing motors. Since…continue reading
High Speed Machining is the use of smaller cutters at much faster spindle speeds and feed rates to make many lighter cuts that take the place of deeper slower cuts with larger cutters in conventional machining. The advantages of HSM include higher accuracy, faster cycle times, and more accurate parts. Cutting forces are diminished in…continue reading
In mechanical engineering, a helix angle is the angle between any helix and an axial line on its right, circular cylinder or cone. The flutes of a milling cutter are almost always helical. If the flutes were straight, the whole tooth would impact the material at once, causing vibration and reducing accuracy and surface quality.…continue reading
A Helical Beam Coupler is a type of shaft coupler that has a helical slot cut through the middle. This allows the coupler to flex which enables coupling of shafts that are not quite true to one another. Helical Beam Couplers are a popular way to couple stepper and servo shafts to the reduction drive.
Heat treatment is a method used to alter the physical, and sometimes chemical properties of a material. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering and quenching.…continue reading
Harmonic drives are gear reduction devices used to couple motors with linear axes. The basic principle used is a “Strain Wave Gearing” mechanism. It is an input/output gearing mechanism. Claimed characteristics include: no backlash, compactness and light weight, high gear ratio, ratio reconfigurable within a standard housing, good resolution and repeatability when repositioning inertial loads,…continue reading
Hardness is the measure of how resistant solid matter is to various kinds of permanent shape change when a force is applied. Hardness is a way of quantifying a materials ductility, elasticity, plasticity, strain, strength, toughness, viscoelasticity, and viscosity. Because of the wide range of alloys and heat treatment techniques applied to metals, it is…continue reading
Handwheels are used to manually move and position a CNC axis by rotating the wheel rather than jogging with a keyboard or pendant. The handwheels are generally connected to an MPG device which sends movement signals to the motor/driver package as opposed to the handwheels being directly tied to the ballscrew. The reason this option…continue reading
A Hall effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. These sensors are used to detect the proximity of linear actuators (i.e. home switches or limit switches) as well as to detect RPM on spindles. The voltage change is usually converted from an analog signal to…continue reading
The hardening treatment for most steels consists of heating the steel to a set temperature and then cooling it rapidly by plunging it into oil, water, or brine. Most steels require rapid cooling (quenching) for hardening but a few can be air-cooled with the same results. Hardening increases the hardness and strength of the steel,…continue reading
Inches per minute (IPM) In the English system, the number of linear inches that an axis travels in one minute. Feedrate is usually given in inches per minute. IPM = IPT x No. Teeth x RP.
The IPAC is a popular keyboard emulator among CNC designers because of its high number of inputs and good design.
An inverter is an electrical device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.
Interpolation is the mathematical method of combining the axes of a CNC machine together to make movement. Since axes can only move at right angles to one another, interpolation is necessary to make that movement useful. There are two types of interpolation: Linear interpolation is the process of combining two or more axes together to…continue reading
An insert drill is a drill with carbide inserts clamped to a steel body. Indexable carbide drills are among the most cost-effective drills. Each drill is designed for a specific size hole. Often, insert drills will have coolant passages to allow coolant to be pumped through the drill and down to the very bottom of…continue reading
Indexable tooling is tooling that uses carbide inserts as the cutting edges (as opposed to high speed steel or cobalt). When the insert dulls or chips, it can easily be rotated to a fresh cutting edge or replaced with a new one for a fraction of the cost of replacing the whole tool.
Inserts are easily changeable cutting surfaces that may be used with indexable tooling. Inserts are generally very cheap compared to the cost of replacing the entire cutting tool, and so provide an economical way to use carbide for high performance cutting in machine tools. Making an entire tool out of carbide would be very expensive…continue reading
A pulse is a logic high signal (usually +5 volts in TTL logic) which is produced by an encoder that is being used to measure spindle position and RPM. This index pulse can be as simple as a mechanical flag passing through an optical switch or as complicated as a servo motor encoder adapted to calculate…continue reading
Incremental Coordinates which are also called Relative Coordinates, refer to the system by which the part program determines how to move. In order to understand Incremental Coordinates, it is helpful to contrast them to absolute coordinates. Absolute coordinates are expressed relative to a fixed position whereas Incremental Coordinates or Relative Coordinates are relative to the…continue reading
Inches per tooth is a unit of measurement for feed that indicates the thickness of material removed by each cutting edge as it enters the workpiece. This measurement confuses some people because the unit of measurement is largely out of proportion. 1 inch per tooth would mean that the machine would be feeding at the…continue reading
The Initial Graphics Exchange Specification (IGES) (pronounced eye-jess) defines a neutral data format that allows the digital exchange of information among Computer-aided design (CAD) systems.
Helical interpolation is the coordinated movement of x, y and z axes to follow along the path of a helix. A related term spiral interpolation describes the coordinated movement of x, y and z to follow along the path of a spiral (i.e. a collapsing helix). Helical interpolation is required when thread milling a straight…continue reading
Idle Current Reduction is a feature in stepper motor drivers that reduces that current by 50 percent or more when not moving. This prevents heat buildup and conserves power. The power is not completely shut off because some holding torque is still necessary to prevent the axes from wandering.
Jogging is simply manually moving and positioning an axis of a CNC machine under power. Using the arrow keys of the keyboard in Mach3 will allow the user to jog the machine into position. Remote pendants are often times used to jog the machine with great control and tactile feedback
Generically jigs are used to guide and hold the workpiece. There is a difference between a jig and a fixture. A fixture simply holds the part. A jig both holds the part and guides the tool; as in a drill jig where the drill is guided by a hardened steel bushing. Jigs are never used…continue reading
A bed mill is a style of mill where the bed is fixed and the Z axis is adjusted by the entire head sliding up and down a verticle column on ways. This is in contrast to a knee-type mill where the bed slides up and down the base on vertical ways. Compare the two…continue reading
Lost steps refers to the condition when a stepper motor is sent a command by the control software, the command is received by the stepper controller and power is supplied to the motor but the motor is unable to execute the instruction. The reason it is called a “lost step” instead of something like “uncompleted…continue reading
Lookahead is a feature of control software, the purpose of which is to look forward in the Gcode to anticipate curves, turns, acceleration or deceleration. This lookahead feature predicts sudden changes in velocity and direction to make more efficient tool paths. Lookahead can be adjusted to manage the tradeoff between efficiency and accuracy.
Load meters are common on CNC machines to give the operator a reliable piece of feedback data indicating how hard the machine is working. Because the axes are moved by motors much of the “feel” is lost. Load meters are simply ampmeters connected to the spindle or axis motor which gives a reading as to…continue reading
Live tooling is a feature that equips the turret of a lathe with power-driven cutting tools such as end mills and drills. These tools can perform cutting operations off-center while the workpiece is held still in the spindle.
A linear slide is a linear bearing (aka truck) matched to a track (aka rail) such that the bearing can travel with very low friction in a linear direction. There are many different styles of linear bearings. Some bearings contain recirculating ball bearings that travel along a corresponding machined groove in the rail. Other…continue reading
A linear scale is used for determining position along a linear axis. The scales are available in two flavors – absolute or relative. Absolute scales are created such that they are able to read there position along the axis without any calibration (much like a tape measure). Relative scales are able to read their position…continue reading
A linear power supply is a DC power supply that produces consistent voltage levels. The voltage produced by an unregulated power supply will vary depending on the load and on variations in the AC supply voltage. For critical electronics applications a linear regulator will be used to stabilize and adjust the voltage. This regulator will…continue reading
Linear motion in the realm of mathematics is motion along a straight line, and can therefore be described mathematically using only one spatial dimension. It can be uniform, that is, with constant velocity (zero acceleration), or non-uniform, that is, with a variable velocity (non-zero acceleration). The motion of a particle (a point-like object) along the…continue reading
Linear Interpolation is a motion type that allows the programmer to command perfectly straight line movements. This motion type also allows the programmer to specify the motion rate (feedrate) to be used during the movement. Straight line motion can be used any time a straight cutting movement is required (i.e. drilling, turning a straight diameter,…continue reading
The term limit switch is a generic term for a sensor or switch at the end of an axis which is placed there to trip an emergency stop situation if the axis for some reason travels that far. In a perfect world, limit switches would never be triggered, but in the real world they are…continue reading
A leadscrew (or lead screw), also known as a power screw or translation screw,is a screw designed to translate radial motion into linear motion. Power screws are classified by the geometry of their thread. V-threads are less suitable for leadscrews than others such as Acme because they have more friction between the threads. Their threads…continue reading
Lead angle refers to the angle of engagement for a particular cutting tool. If viewed from above looking down on the cutting tool, it is the angle formed by the side flank of the tool and a line perpendicular to the workpiece centerline. A positive lead angle moves the side flank into the cut, and…continue reading
The terms “lead-in” and “lead-out” refer to how a CNC part program approaches and leaves the part when cutting. Most CAM programs have parameters for describing the type of approach and exit strategy that will be employed in cutting a part. These cutting strategies can range from directly plunging and retracting the tool (no lead-in…continue reading
Lead refers to the axial distance the nut advances in one revolution of the leadscrew. The lead is equal to the pitch times the number of screw starts.
A laser interferometer system employs a highly stabilized light source and precision optics to accurately measure distances. Interferometers are superior to glass encoders for several reasons. The most obvious advantage is that interferometers have greater inherent accuracy and better resolution. An additional advantage is that interferometers measure distances directly at the workpiece. Due to mounting…continue reading
Lapping is a machining operation, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine. This can take two forms. The first type of lapping (traditionally called grinding), typically involves rubbing a brittle material such as glass against a surface such as iron or…continue reading
Ladder logic is a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay-based logic hardware. It is primarily used to develop software for Programmable Logic Controllers (PLCs) used in industrial control applications. The name is based on the observation that programs in this language resemble ladders, with…continue reading
Many G codes and M codes cause the machine to change from one mode to another, and the mode stays active until some other command changes it implicitly or explicitly . Such commands are called “modal“. Modal codes are like a light switch. Flip it on and the lamp stays lit until someone turns it…continue reading
Motion control is a sub-field of automation, in which the position and/or velocity of machines are controlled using some type of device such as a hydraulic pump, linear actuator, stepper or servo motor coupled with a control signal. CNC machines are a subfield of this subfield. In other words, CNC motion control is just one…continue reading
Moglice is an epoxy resin with embedded PTFE that is used to refurbish or line machine ways. The material is poured or injected onto the surface of the ways and then spread and squeezed to the proper shape. Once properly appied it is then scraped or machined flat to provide a low friction bearing surface.
The ModIO is a modbus controller by Homann Designs. These modbus devices are designed to provide additional inputs and outputs to controllers such as Mach3 and others. Rather than using the parallel port, modbus controllers rely on serial ports making them an excellent choice for reliable expansion. Below are the specs from the Homann…continue reading
Modal G and M codes are codes that change the state of a CNC machine. Many G codes and M codes cause the machine to change from one mode to another, and the mode stays active until some other command changes it implicitly or explicitly . Such commands are called “modal“. Modal codes are like…continue reading
Mist cooling employs droplets of coolant or oil suspended in a compressed airstream. Mist cooling is a good alternative when flood cooling is not practical.
A microswitch is a type of swtich that makes contact with very little travel and as such make excellent homing and limit switches. In addition, many microswitches are designed to be highly precise and accurate (a requirement for homing switches). Illustrated are several different styles.
Microstepping is technique used by stepper motor controllers to increase the resolution and/or reduce vibration and resonnance of a stepper motor. Most stepper motors have 180 steps per revolution or 1.8 degrees per step. This resolution is in fact a function of the way the motor was wound. The theory behind microstepping is to “cheat”…continue reading
MDI or Manual Data Input refers to the manual entry and execution of G-Codes from the keyboard. In Mach 3 there is a special tab labelled MDI for this very purpose.
M-codes are best thought of as miscelaneous controller specific functions that do not fall under the normal G-code standard. Some M-codes have become somewhat standard (ie. tool changes, turning on or turning off the coolant or spindle) but they are usually fairly specific to the controller, and are not well standardized. Some controller programs, such as…continue reading
Manual Pulse Generators or MPGs are handwheels used on CNC machines to simulate the handwheels on traditional milling and lathe machinery. The configuration usually includes a physical handwheel attached to a rotoary encoder which sends signals to the driver to move the machine.
Machine Zero refers to the extreme edge of a particular axis. Machine Zero is synonymous with the Home Position of the machine. Many machines will have Home Switches at this location so that the axes can be commanded to move until the Home Switches are triggered, telling the machine it is exactly at Machine Zero…continue reading
Machine coordinates refers to the absolute physical coordinates of a machine. Since these coordinates are measured from the home position (0,0,0), they will always be a positive number.
Mach 3 is the name of a very popular, very affordable CNC control software package that runs under windows and is sold by a very industrious man named Art under the banner of the company ArtSoft. The forums and support community is very mature and has been extensively developed. Earlier versions of this software were…continue reading
Mach 3 is the name of a very popular, very affordable CNC control software package that runs under windows and is sold by a very industrious man named Art under the banner of the company ArtSoft. The forums and support community is very mature and has been extensively developed. Earlier versions of this software were…continue reading
Non-uniform rational basis spline (NURBS) is a mathematical model commonly used in computer graphics for generating and representing curves and surfaces which offers great flexibility and precision for handling both analytic and freeform shapes.
Normalizing is a type of heat treatment applicable to ferrous metals only. It differs from annealing in that the metal is heated to a higher temperature and then removed from the furnace for air cooling. The purpose of normalizing is to remove the internal stresses induced by heat treating, welding, casting, forg- ing, forming, or…continue reading
NEMA (National Electronic Manufacturers Association) is an international electric standards association. The name comes up when referencing motor sizes in CNC design. Common sizes are NEMA 23, 34 and 42. See our chart for dimensional information.
Negative rake refers to angles less than 90 degrees to the workpiece. Rake is the angle from the workpiece wall to the cutting tool at the cutting edge. If it is 90 degrees, the edge is perpendicular to the workpiece. Angles less than 90 degrees are negative rake angles. Angles greater than 90 degrees are…continue reading
N Code simply refers to the line numbers in a given program file.
Oz/in is a unit that measures torque. 1 ounce / in = 1.11612296 kg / m. Stepper motors and servo motors are always rated in ounze inches of torque.
The origin is the reference point off which a particular coordinate system is based. In absolute coordinate systems, this origin is in a fixed location (usually the homing switches on a particular machine). In relative or incremental, the origin is a user specified location. Both systems have their uses and advantages.
An optical isolator, or optical diode, is an optical component which allows the transmission of light in only one direction. These electrical circuits are used to electrically separate two components to prevent feedback and electrical damage. The most common use of these devices in CNC machines is to separate the high power drivers from the…continue reading
Optional stop refers to a code that is sent which pauses the program if the appropriate switch is selected on the machine. Optional stops allow the operator to inspect the machine between operations. If the block contains an M1 code and the optional stop control is on, the machine to pause for operator inspection.
Open loop feedback systems might be better named no-feedback systems. These types of controls know where the machine should be but not actually where it is. The most common application of this system is the stepper motor/driver combination. These systems do not have any sensors to determine if its commands were in fact carried out.…continue reading
An open collector is a type of output on many integrated circuits (IC). Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized (open) on a pin of the IC. The emitter of the transistor is connected…continue reading
An oldham coupler is a mechanical device which transmits rotary motion between shafts that are parallel but not always in perfect alignment. The oldham coupler is built around three discs, one coupled to the input, one coupled to the output, and a middle disc that is joined to the first two by tongue and groove. The tongue…continue reading
Offsets refer to a compensation distance from a known point. For example, a CNC machine might have a tool offset programmed into it so that the machine knows the “zero” Z height of a particular tool. The offset in that case would be the length of the tool. Other usages of offsets include radius of…continue reading
A quill drive is a mechanism that allows a drive shaft to shift its position (either axially, radially, or both) relative to its driving shaft. It consists of a hollow driving shaft (the quill) with a driven shaft inside it. The two are connected in some fashion which permits the required motion. One example of…continue reading
Precipitation hardening, also called age hardening, is a heat treatment technique used to increase the yield strength (the point at which it deforms plastically) of malleable materials. 2000, 6000 and 7000 series aluminums use this method to obtain their unique characteristics
Pulse-width modulation (PWM) is a very efficient way of providing intermediate amounts of electrical power between fully on and fully off. A simple power switch with a typical power source provides full power only when switched on. PWM is a comparatively recent technique, made practical by modern electronic power switches. In the past, when only…continue reading
Pulse rate refers to the speed at which signals are being sent over a digital circuit (the speed at which the digital signal switches from 0 or low to 1 or high). For example, a given pulse rate might define the number of steps being sent to a stepper motor over a specified period of time…continue reading
In chemistry, polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon. Because of its low friction qualities it is used on some bearings and linear ways.
A proximity switch is a sensor able to detect the presence of nearby objects without any physical contact. The ability to detect objects without actually touching them is what separates a proximity switch from a limit switch. A proximity sensor often emits an electromagnetic or electrostatic field, or a beam of electromagnetic radiation (infrared, for…continue reading
Preloading is the methodology by which we remove the internal clearance in the bearing by applying a permanent thrust load to it. Bearings apart from being mounted on the shafts and housings have to be preloaded properly for their proper functioning. In other terms we can say that we push the bearing…continue reading
A powered drawbar typically uses an air or electric impact wrench to operate the drawbar mechanism under power. It’s advantages over a manual drawbar include much faster operation together with more repeatable torque on the drawbar. A powered drawbar is a much less expensive, less complex way to speed up tool changes than an automatic…continue reading
Posting usually refers to the act of sending G-Code from a CAM program to the CNC machine. Because there are many different machines each with their own slightly unique flavor of Gcode controllers, it is necessary to have a machine-specific postprocessor so that the Gcode created in the post is readable by your particular machine.
Positive rake referes to a rake angle greater than 90 degrees. Rake is the angle from the workpiece wall to the cutting tool at the cutting edge. The back rake angle affects the ability of the tool to shear the work material and form the chip. Positive rake angles reduce the cutting forces resulting in…continue reading
Pocket milling is an interior recess that is cut into the surface of a workpiece. Pockets may be round or rectangular. The photo pictured is an example of a pocket milling operation.
Plunge refers to a cutting tool moving straight down in the Z direction. Spiral type cutters are especially well designed for plunging since they are able to remove material that would otherwise collect beneath the bit. Plunge operations are an essential part of pocketing operations.
Plasma cutting is a process that is used to cut steel and other metals of different thicknesses (or sometimes other materials) using a plasma torch. In this process, an inert gas (in some units, compressed air) is blown at high speed out of a nozzle; at the same time an electrical arc is formed through…continue reading
Pitch refers to the axial distance between threads. Pitch is equal to the lead in a single start screw. Pitch is often confused with lead. Lead refers to the axial distance the nut advances in one revolution of the screw. The lead is equal to the pitch times the number of starts. LEAD = PITCH…continue reading
Pinch turning is a way to employ 2 independent tool turrets on a CNC lathe in order to cut more quickly. When pinch turning one tool follows behind the other cleaning up the path left by the first tool. Pinch turning is also referred to as balanced turning. It can be used for either roughing or…continue reading
A proportional–integral–derivative controller (PID controller) is a generic control loop feedback mechanism (controller) used in CNC servo control systems. A PID feedback controller calculates an “error” value as the difference between where it “should be” and where it actually is. The controller attempts to minimize the error and maximize efficiency by adjusting the control variables.…continue reading
In peripheral (or slab) milling, the milled surface is generated by teeth located on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the workpiece surface to be machined as shown in photo.
A pendant is a handheld control for positioning a CNC machine. Often times it is awkward or impractical to move the machine from the actual CNC controller so a pendant gives the operator freedom to jog and control basic functions from a wide range of locations. This is particularly helpful in setup and fixturing.
Peck drill is a “canned cycle” drilling operation in which the bit advances into the hole retracts to clear chips and/or flood the hole with coolant and then advances further, retracts, etc. Peck drilling is often used for holes that are three or four times deeper than the drill diameter.
P-code is a program code that indicates the name of the subprogram to execute.
A part program is the file read by the CNC controler to actually move the CNC machine and cut a part. It is often times referred to a simply the “gcode file” but this is technically incorrect because gcode refers to one “word” within the many different types of “words” within the part program file.
Parametric programming can be compared to very simple programming language. The word parametric refers to the fact that “parameters” or variables are availabe for use in a line of G code programming. This would be used for a family of parts, or situations that are used repeatedly in different parts. Let’s say you drill holes…continue reading
Quadrature oscillations are said to be in quadrature if they are separated in phase by 90° (π/2, or λ/4). Quadrature encoders are generally used to measure angular position, often of something like a rotating shaft. A quadrature encoder has a specified resolution, like any other encoder, that indicates how many pulses determine a full revolution…continue reading
A parallel port is a type of communications interface sometimes known as a printer port or Centronics port. The IEEE 1284 standard defines the bi-directional nature of the port, which transmits data bits at the same time (in “parallel”). This is the opposite of serial transmission where one bit is transmitted at a time. Parallel…continue reading
RS274D is the Electronic Industry Association standard that defines the G-Code CNC language used by nearly all CNC machines. This version was approved in February, 1980. A more recent definition by NIST is called RS274NGC, with the “NGC
RS232 is a serial communication standard. It is most commonly utilized in PC serial ports but is also used in CNC controllers. It’s function in the CNC industry is transferring program files via a DNC console or in expanding the functionality of a machine via a modbus controller. See our RS232 specifications page for details…continue reading
A round column mill is similar to a drill press in that it uses a round column to support the spindle. Z-axis moves are made using a quill because the spindle cannot be moved along the column without losing x and y position. They lack the rigidity of kneemill style mills and are plagued by…continue reading
Roughing refers to an initial pass of the cutting tool that emphasizes heavy metal removal rates, high feed rates, and a heavy depth of cut. It is called a roughing cut precisely because these high removal rates produce a very “rough” finish. The obvious advantage to roughing is time savings.
The Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, which are denoted by a single letter, that use…continue reading
R-level can be thought of as the rapid-to start point. The R-level is the starting point of the cutting feed rates and also the point to which the tool will retract after finishing the cutting operation. This retraction height must be higher than any point on the workpiece and for this reason R-level is sometimes…continue reading
Rigidity or stiffness is the resistance of an elastic body to deformation or deflection by an applied force along a given degree of freedom. In simple conceptual terms a steel I beam is makes a much more stiff or rigid catwalk than a piece of pine lumber (i.e. it does not flex under load).
Rigid tapping or synchronous feed tapping is a tapping technique used in CNC machines where the tapping cycle synchronizes the machine spindle rotation and feed in the z direction to match a specific thread pitch. Since the feed into the hole is synchronized, in theory a solid holder without any tension-compression can be used. However…continue reading
The right hand rule is a handy quick reference technique that shows the X, Y, and Z-axes of a standard mill setup. A person displays his or her right hand (with thumb pointed to the left, and the first three fingers from the right each represent the X (thumb), Y (pointer), and Z-axis (middle) in…continue reading
Rhino3D is a 3 dimensional CAD package that is popular among CNC enthusiasts. It is particularly appealing because of its powerful yet intuitive modeling capabilitie, its focus on NURBS modeling and the available CAM plugin named RhinoCAM. Having both CAD and CAM packages available in one software package is highly valuable.
A retention knob (aka pull stud) a knob on top of a toolholder that the drawbar uses to grasp the toolholder and pull it into the taper. The retention knob is gripped by a claw on the end of a drawbar. It makes for much faster engagement than a threaded drawbar. Retention knobs are replaceable…continue reading
In physics, resonance is the tendency of a system (usually a linear system) to oscillate with larger amplitude at some frequencies than at others. These are known as the system’s resonant frequencies (or resonance frequencies). In CNC world, stepper motors are the greatest cause of resonance at certain step rates. This can be seen as…continue reading
Resolution refers to how accurately a CNC machine or component can discern position. For example a machine may have a resolution of .001 which means that there are physical limitations on ever stopping at .0005. Because of limitations in components such as the motors, encoders or ballscrews the machine will “cog” either to one side…continue reading
Repeatability is the variation in measurements taken by a single person or instrument on the same item and under the same conditions. Repeatability for a CNC machine is the ability to reach the same level of accuracy over and over again.
Relative coordinates refer to a point from where the position is right now to where you want to go. Absolute coordinates refers to a new location from an absolute zero point on the machine (i.e. the homing switches). Example: Lets say that you are currently sitting at zero in X, Y and Z you need…continue reading
A regulated power supply is one in which a voltage regulator circuit or component has been added to ensure voltage stays at a pre-determined level as precisely as possible. The voltage produced by an unregulated power supply will vary depending on the load and on variations in the AC supply voltage. For critical electronics applications…continue reading
A refractometer is an optical device used to measure the index of refraction of a material. In CNC use, refractometers are used to measure whether coolants, which are made from concentrate, are mixed in the correct ratios. Failure to mix a coolant properly can lead to sub-standard performance as well as a greater likelihood the…continue reading
Recutting refers to the situation in which a chip is not evacuated from the cutting area and “re-cut” as it is once again forced against the tool and the wall of uncut material. Recutting can be minimized by using coolant to evacuate chips as well as using climb milling instead of conventional milling.
A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification. A device which performs the opposite function (converting DC to AC) is known as an inverter.
Rapid travel refers to a G0 command which moves the machine at the maximum programmed rate of speed in order to reposition the cutter to a new location prior to beginning a new cut. Rapids can be many times faster than cutting speeds. Since a significant portion of time is spent repositioning the tool, it…continue reading
Ramping is used in two different senses in the world of CNC. For a stepper motor, ramping is a technique of controlling the acceleration or deceleration of the motor to ensure it arrives at the desired speed when expected. Physics demands that acceleration takes time. The faster the acceleration the more power it takes. Setting…continue reading
Rack and pinion is a type of mechanism for translating rotation motion to linear motion. It consists of a rack, which is a long toothed rod, and the pinion, which is a round gear that engages the rack. Rack and pinion setups have the advantage of being less expensive than ballscrew technologies but suffer many…continue reading
An R8 taper is a type of taper designed by Bridgeport Machines, Inc. for use in their milling machines. It is used with a drawbar extending up through the spindle to the top of the machine to prevent the collet from falling from the spindle when lateral forces are encountered. The collet, which is inserted…continue reading
Typically, the limits of a CNC machine are controlled by “limit-switches.” When a machine hits these switches, the machine automatically stops. Soft limits refer to the ability of the CNC control software to set limits on axis travel in the software. Once set, the software should never command the axis to move beyond the limits.
A solid state relay is a relay without moving parts. A traditional relay has a moving arm controlled by a solenoid to switch the current from one pole to another. Solid state relays accomplish this same task electronically without moving parts. Solid State relays can work with either AC or DC current.
A very popular CAD program used by CNC professionals around the world. It’s professional feature set unfortunately comes at a professional price and as such is typically out of reach for the hobbiest.
Carbon steels and alloy steels are designated by a four digit number, where the first digit indicates the main alloying element or elements, the second digit indicates the secondary alloying element or elements, and the last two digits indicate the amount of carbon, in hundredths of a percent by weight. For example SAE1040 denotes plain…continue reading
Work hardening, also known as strain hardening, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements within the crystal structure of the material. Any material with a reasonably high melting point such as metals and alloys can be strengthened in this fashion.
A switching-mode power supply is a power supply that provides power through low loss components and a switching regulator in order to provide the required output voltage. The function of the converter is to provide a regulated output voltage usually at a different level than the input voltage. Unlike a linear power supply, the pass…continue reading
A swiss lathe is a modified automated turret lathe distinguished by a sliding headstock and fixed bushing. The work is fed through the spindle to provide Z-axis motion. (i.e. the tooling does not move in Z). Most lathes keep the workpiece fixed and only the tool moves in relation to the rotating workpiece. Swiss lathes excel…continue reading
Surface speed refers to the speed of the of the workpiece relative to the tool (or depending on perspective the speed of the tool relative to the workpiece). Surface speed is measured in surface feet per minute. Typical values for various materials are given in the chart below. Material type Meters per min (MPM) Surface…continue reading
STL is a file format native to the stereolithography CAD software created by 3D Systems. This being said, the file format is supported by many other software packages. It is widely used for rapid prototyping and CAM packages. STL files describe only the surface geometry of a three dimensional object without any representation of color,…continue reading
Stick-slip refers to the physical phenomena of an object sliding across a surface and then sticking to the surface as the speed decreases. The reverse can also be true where a force is applied to a stationary object and when the force overcomes the friction there is a sudden jerking motion as the “sticking” changes…continue reading
A stepper motor (or step motor) is a brushless, synchronous electric motor that can divide a full rotation into a large number of steps. The motor’s position can be controlled precisely without any feedback mechanism (see Open-loop controller), as long as the motor is carefully sized to the application. Stepping motors can be viewed as…continue reading
Step-over refers to the percentage of the cutter’s diameter that is engaged in a cut. When performing a pocketing operation or any operation that removes large amounts of material, many passes are required. It is not advisable to engage 100 percent of the tools diameter in each pass since some material might be missed. Cutting…continue reading
Step and direction signals refer to the control logic used to control stepper motors. The stepper motor controller typically accepts two inputs from an external source: step and direction. The direction signal set the direction of rotation and each pulse on the step signal causes the controller to move the motor one step in that…continue reading
STEP files refer to a universal file format to enable cross compatibility in the maching industry. In design and manufacturing, many systems are used to manage technical product data. Each system has its own data formats so the same information has to be entered multiple times into multiple systems leading to redundancy and errors. The…continue reading
A square column mill is simply a bed mill with a square column equipped with a dovetail way to allow adjustment along the z-axis. Usually square column mills are compared with round column mills. The round column head can rotate around the column 360 degrees; the dovetail version cannot. On the other hand, when Z-axis travel…continue reading
a spindle speeder is an attachment for a milling machine that contains a gearbox that multiplies the speed of the spindle enabling improved cutting performance in heavy-duty machining, engraving and fine finishing. Spindle speeders can maintain high speeds up to 40,000rpm.
Spindle sensor refers to a sensor installed on the spindle of a lathe or mill. These sensors are used to measure the speed and sometimes the position of the spindle. It is particularly important to understand spindle speed when threading (on a lathe) or tapping (on a mill). The sensor comminicates to the control program,…continue reading
Similar to Feed Override, Spindle Override lets the operator manually change the spindle speed during operation to increase or decrease it by a percentage of the programmed speed for fine tuning purposes.
The spindle of a machine is the bearing assembly that rotates either the workpiece or the cutter at high speed for machining. Types of spindles range anywhere from heavy duty 2000 rpm low speed spindles to 50,000 rpm high speed spindles.