Complete Rebuild Part 1

So basically, I am going to totally strip this puppy down and rebuild the X and Y Axis.  I am also going to replace the steppers on the X and Y Axis with servos.  There are several reasons for the rebuild.

• Poor dust collection has totally clogged and rendered the machine out of service.  So if ever there was a time to do some upgrades it is now.  I have to tear it apart either way.  Obviously my poor dust collection cannot go on, so I am spending a lot of time and effort making the ultimate dust shoe that will hopefully address/solve everything that bugs me about dust collection in general.  I have started an entirely separate design group to document that progress.  It can be found here
• My current design is a dual ballscrew setup.  I want to change to a single ballscrew.  Some people swear by dual ballscrew configurations, but they don’t work well for me.  First I do not like the fact that I have to calibrate them every single time I start up the machine.  Secondly, I cannot comfortably try to push this axis to its limits since the consequences of just one of my steppers stalling is so horrendous that I play very conservatively.   During a cutting operation a while back, I was pushing the limits a little too far and the inevitable happened.  One motor stalled while the other kept turning (sounds that ought to be kept to the imagination).
• Stepper to Servo conversion for higher reliability and faster speeds.  Steppers suffer from low torque at high RPM and a low RPM top speed.  Secondly, the open loop design of steppers leave open the possibility that one’s machine will loose steps and you will never know until the part is finished and the part isn’t quite right.
• Dust collection revamp.  Not only do I want to make a better dust shoe to collect at the source, but I want to make my X and Y ballscrews enclosed so they do not loose performance from airborn dust particles clogging the ballnut.

After this heroic effort I came inside and was greeted by my wife who said, “You stink like oil.”  Such appreciation

Videos of Z Axis in Motion

Basic Photo Build Log

I’d like to document my Steel CNC build.  This CNC machine is my second one (really my fourth one if you count my middle two abandoned attempts).   My first CNC machine was a proof-of-concept MDF beast.  I learned a lot but I wanted to make something that would be far more adjustable and more precise.   Secretly I wanted to keep my options open and really liked the idea of playing with a 4th axis.  The unique advantage to this design is the adjustable table.  This picture gives you a good idea of how the table moves up and down. The entire table glides on 4 THK linear bearings sliding on 1.25” hardened rods tapped on both ends.  I was very worried initially about how in the world I was going to align those four rods so they would not bind, but as it turns out this is a much easier process than one might think. The four vertical rods are tapped on either end so that they will receive 1/2-13 bolts.  I simply overdrilled the holes in the steel frame and once the table was in place, moving it up and down causes the four rods to perfectly self align and from their it’s just a matter of slowly tightening down the rods one at a time in sequence.

I started with this picture to give the reader an idea of where I was going with the design but truth be told, I should honestly start with this this picture because this “score” on ebay is what really started the whole thing.  I didn’t have the time or money for another project, but how could I turn down this deal.  Ebay is the hobbiest dream sourcing solution. There is absolutely no way anyone could create high quality industrial strength machinary at hobbiest pricing without ebay!

The unit that I picked up from the best of my research came off of a CNC machine similar to this one. The rigidity of this assembly is what impressed me the most. the y-axis crossmember was a solid piece of aluminum measuring 28 inches accross 7 inches high and two inches thick and weiging close to 100 pounds. The aluminum alone at scrap metal pricing was worth 150 bucks. Igus cabling, a stout z axis aseembly complete with stepper motor and various other misc items, made this the perfect starter kit for my final CNC project. The cost? A mere 190 dollars including shipping. I sold of the linear motor and controller that came with the unit making the total cost of ownership about 100 bucks. Can’t complain about that!

The unit I purchased came with a linear magnetic motor instead of the traditional ballscrew for the y axis. This is a picture of the controller that came with the linear motor that I pawned off on ebay. Although very cool concept in real life, I had now way of controlling it with my software.

Here is a close up of the Z axis assembly as I received it. The Z axis rides on some THK linear slides and then is driven by a Pacific Scientific stepper motor/ballscrew comination unit. The entire z axis rides on second set of larger y axis THK slides. Overall the assembly is quite rigid and about a 1000 times more industrial than my previous wooden version.