So, you got a new CNC Router

Shinny New Probotix Fireball Comet CNC Router

You built a table for it.

Router on Basic Table

Now What?

Where I started is with a containment box. A containment box keeps dust and all but the most energetic shrapnel from flying into the rest of the shop.

Safety note:

This containment box has not been tested in a manner that allows it to be called a safety device. It will HELP keep flying objects contained, but by its self, it is not sufficient protection. ALWAYS wear safety glasses. ALWAYS position a safety switch where you can quickly reach it. ALWAYS wear hearing protection. If you do not have a dust collection system, you must wear a high quality dust mask.

Frame Construction

The box is made of a wooden frame with heavy gauge clear vinyl sheeting attached using wood staples and velcro.

The wooden frame consists of twelve pieces of 1 inch by 2 inch pine boards that are connected together using angle plates.

Frame Pieces and Most of the Hardware

Please take a look at the Containment Box Design PDF file.  Note how the lumber is orientated in each of the views.  A 1by 2 is actually 0.75 inches by 1.5 inches.  It makes a difference which way the lumber is orientated; not only get the desired dimensions for the box, but also to control how stiff the frame is in each direction.  This was especially important in my application since the edge of the box needed to extend beyond the table edge on one side.

The box and the router both sit on the table.  Since the Y axis stepper motors are just above the table top level, the length inside the wood pieces had to be longer than the length from the end of the stepper to the back end of the  table. Going side to side,  the widest area is where the X axis stepper motor is attached to the gantry.  Because of that, the  width inside the frame can be a little shorter, but keep in mind that if you run a vacuum system, the vinyl sides of the of the box will be pulled in some  and the stepper will rub against the vinyl.  Vertically, you have a similar problem.  Both gravity and suction will try to sag the top vinyl.  You need to add some additional clearance above the highest point your Z axis components can reach to account for the sag.

Metal angle brackets are used to secure the lumber pieces together.  Since the vinyl needs to fit up against the lumber, the metal angles can not be on outside of the box.  This means you have to think a bit about where and how you place your angles to keep them from interfering with the lumber that will come in perpendicular to the joint you are currently assembling.

assembling a corner

In the photo, you can see the angle bracket on the joint.  I placed it closer to the inner edge of the lumber instead of the center.  This is to provide room for the third piece that will attach at this corner.

The joint is being held square by a corner clamp.  These clamps are very handy for many projects.  It is worth investing in four of them.

I used a transfer punch to mark the hole locations for the bracket.  A transfer punch only works if there is some depth to the object from which you are transferring the hold center.   Angle brackets have a spot face on them to allow the head of the mounting screws to be flush with the bracket.  The spot face would prevent the center punch from lining up correctly with the center of the hole, so, as shown in the picture, the bracket is initially placed upside down on the lumber (ie, the spot face is toward the lumber instead of away from it).  This makes the hole the smallest at the greatest distance from the lumber.  This allows the transfer punch to go in straight.  Since the hole locations are symetrical, the hole centers will still be in the right place when the bracket is flipped over.  Once the holes are marked, remove the bracket.

You should always pre-drill holes for wood screws.  The drill should be about the same diameter as the screw shaft without the threads.  Hold the screw up behind the drill bit you plan to use. if you see the screw’s threads, but not its solid shaft on both sides of the drill bit, you have the correct bit.  You do not want to drill all the way through the wood.  Use several turns of electrical tap around the drill bit with the front edge of the tape being just a little closer to the tip of the drill than the last thread on the screw is to the tip of the screw.  Don’t rely on the tape as a physical stop.  The edge of the tape will get pushed back by the lumber so successive holes will keep getting deeper.  Watch the bit and stop when the tape is just touching the lumber.

Now is a good time to talk about the quality of the brackets and screws.  General merchandise stores like Wall Mart carry brackets.  They are nice and shinny, but they are made as cheaply as possible.  This is not a big deal for the bracket its self, but it is dangerous for the screws.  Or, more accurately, cheep screws are dangerous for you.  To get a good bite in the wood, a significant amount of torque is applied to a screw as it is turned into the wood.  If a powered screwdriver or a drill are used to turn in  the screw, even more torque is applied.  The screws will actually get hot.  The general merchandise screws are basically pot metal.  They deform and fail, usually just below the head.

You are going to be moving around a frame where some of the pieces will be on long lever arms.  If two inside corner brackets are holding an end of the frame and one of the screws on one of the brackets fails, the end of the frame will rotate on the remaining screw.  If you hand is close to the joint, the skin of your fingers can get pulled into the joint and pinched hard enough to cut a chunk out of you finger.  Because of the large mechanical advantage, it will be difficult to rotate the frame back to free your finger.

Want to take a guess how I know this?

The brackets sold in most hardware and home improvement stores are a bit better.  The screws are higher grade and much less likely to snap a head.  Still, you should always use caution when moving the box frame.  Always assume that the structure can fail and move at any time.  Try to keep your hands clear of the joints.  If you can stand it, wear assembly gloves (thin work gloves).  The glove will get caught in the joint instead of your skin.

I started by assembling the ends of the box using flat brackets.

Containment Box End

I then used the corner clamps to hold the end of the box vertical and added the length wise pieces.  Each lenght wise piece was held in place using two internal corner clamps.

A completed corner

Here is somthing to think about as you attach that final piece: how are you going to put the frame over the router?  Do you have enough height in your shop to lift the completed frame over the top of the router?  If you do not, unscrew the piece that will be the lower back part of the frame, leaving the vertical internal corner brackets attached to the piece you are removing, and the horizontal brackets attached to the rest of the frame.   This way, you will be able to slide the frame around the router and then easily reattach the removed part of the frame.

Skinning the Frame

The skin of the containment box is heavy gauge, clear vinyl.  If you have an old relative who covers their furniture, this is the stuff they use.  You can get it at most fabric shops such as JoAnn’s in the US.  Get as thick of material as you can.

When a piece of debris is kicked up by the router and hits the vinyl, it tries to accelerate the vinyl.  Thicker material has more mass so it will take more energy away from the debris.  Since the vinyl is flexible, it will not all accelerate at once.  Instead, it will accelerate in concentric rings.  The slower accelerating outer rings will try to pull back the inner rings.  Since vinyl is a long, smooth chain polymer, the difference in acceleration will cause the material to stretch instead of fracture.  This will also take energy away form the debris  As the material stretches, it gets thinner.  Starting with a thicker piece will give it more time to absorb energy from the debris by stretching before it is finally punctured.

There are two primary ways the vinyl can be attached to the frame.  On edges where you are not going to need to remove the vinyl, you can use wood staples.  Everywhere else, you can use industrial strength Velcro.  You should make your containment box so that it can be opened from at least three sides.  This will make life a lot easier when you need to clean or lubricate the router.  Even if you are going to push your router table into a corner so that typically you can only reach two sides, keep one more side removable.  Trust me on this; it will come in handy latter.

For my box I chose to cut three main pieces of vinyl.  One piece was to be on the back end, one piece on the front end, and then a third piece was to go over the top and cover both of the sides.  Since my box extended out further than the edge of the table one additional piece had to be cut to cover the strip of the bottom of the box that extended beyond the table.  Since I wanted to minimize the places where air can get into the containment box the front piece the back pieces had to be cut long enough that they not only covered the ends but overlapped onto the top a small amount.  by attaching these pieces first and then laying the top piece over them.  I was able to keep nice clean edges on the box.

pulling the vinyl tight on the frame

The trick to attaching the vinyl this to make it as snug as possible. To keep the vinyl snug, I held the first edge of the vinyl to the frame using masking tape.  I would then use clamps on the other end to hold the vinyl to the box.  That way, I could keep adjusting the fit of the vinyl until it were no wrinkles and it and it was very tight on the frame.  Once I was satisfied with the position of the vinyl, I started in the center of an edge and work my way out to either side, pulling on the vinyl while I was doing this to make sure that it stayed very snug. I wanted to make sure that the Staples would not push all the way through the vinyl cause it to rip, so I had the setting on the staple gun set slightly light.  This causes Staples to stick out some from the frame.  I finished tapping the Staples in with a hammer to make sure that they were nice straight and were holding tightly to the vinyl without ripping through it.

Staples

Since the piece on the back end was not going to be removable, I stapled the vinyl all the way around it on the frame.  The front piece, however needed to be able to be opend.  So, I stapled the top edge of the vinyl and applied industrial strength Velcro to the frame and the vinyl on the other edges.  I put the hook side of the Velcro on the frame and I used wood staples in addition to the sticky back on the Velcro to attach to the frame.  I then attached the “furry” side of the Velcro to the vinyl.  Since the adhesive stuck very firmly to both the Velcro and the vinyl, I did not have to add any extra means to secure the two of them together.

Velcro stuck and stapled to the frame

MORE TO COME…