DIY Numpad: Squareness

Over the last week I've done some more work, cutting out the USB slot, making a new case, and figuring out how to get better alignment. For the USB slot, I turned the case on it's side, zeroed in on the top left corner of face, and ran a simple pocketing operating to make the hole:

I clamped the case between a piece of MDF I screwed into the CNC table and a free piece of MDF.

Some shifting.

One clamp wasn't enough to hold it in place, and for the next case I used two clamps.

I began making another case, this time with another set of mirrored alignment holes. I also leveled out the waste board with a simple facing operation.

Added another hole at the top.

5x5 pocket cut out for the stock to be flat.

I ran the backside operation, which went smoothly. After I flipped over the part, I could still only get the holes on one side to line up with pins; the far side holes didn't line up perfectly. Now I realized what the problem was: my CNC's X and Y axes weren't perpendicular! I never realized this earlier because I never tested the squareness of my parts, and a double sided milling operation would effectively double the skew error. This also explains why the wood top case I made before doesn't line up well either since it was machined top side down (the error in screw hole position is effectively doubled by trying to mate a piece machined right side up and a piece top side down).

After some fiddling with the 8020 extrusions and the only square I had around, I think I have the axes dialed in fairly well. I just bought a machinist's square and you can clearly see the error in the last case:

Gap.

I lined up the holes I already made from the backside the best I could (effectively getting all the pins in with force so there would be a little error in all the hole positions, but no single hole far off like with the previous case) and continued on with the front side operations just to see how the case would turn out:

Actually not that bad.

Case in the light.

Surface finish questionable.

Better, but probably need to slow down.

Things lined up fairly well, I just couldn't use all the screw holes immediately because the aluminum plate was also made with the axis error. The next day I made the top part of the case:

Left: success; right: failed	Surface finish.
After heating, there is some optical aberration.	Same aberration.

The first one was scuffed because I didn't mount the middle piece down well, so the finishing pass knocked the floating piece from the middle contour, and the edge of the stock wasn't held down so when it was on the last pass, the thin edge vibrated and cause some terrible gouging. I fixed this on the second time around.

I tried heating the screw inserts, but it creates a visible defect in the clear acrylic. I just superglued in the rest of the inserts. for the next top case I make, I need to make the insert holes deeper since the screws hit the end before tightening the top to the bottom of the case.

Putting it together though:

Clear is the way to go.

The numpad looks far nicer that I expected. Things don't line up perfectly yet since the bottom holes were still made before the alignment, but after I make the changes to the insert holes and re-mill everything, the next case should go together perfectly.

I tried making another wood version of the top section of the case, but the crack in the wood caused some problems:

A crack in the left side caused the wood to become free to flap up and forced me to stop the program. I'll try again another time.