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The current way of making perforated angle is fairly time consuming: print, cut, puncture and attach labels, saw long angle into pieces, and then center punch the pieces from which lables will be removed - for example, those that will be used as linear rails. Most printers do not print the labels to exact dimensions, forcing to resort to cheats and workarounds. Then there is also drilling, however the current approach is to drill holes on demand.

I spent a couple of evenings trying to figure out why a pair of 3ft 1/4-20 rods bind in the coupling nuts for seemingly no reason. Attempted remedies included WD-40, turning rods in sandpaper, cleaning them with brushes, more WD-40.. Finally, in a moment of enlightenment I grabbed a caliper and sure enough, 20 threads measured 1.014". Basically, I have a few feet of 1/4"-19.724 TPI threaded rod. Today I ordered 12ft from Mcmaster, and I'm not getting it in Home Depot anymore.

In the meantime, I've been thinking about adding channel profile to Contraptor. One reason is reducing amount of angle spent working around the fact that it can only be mounted from two sides. Another reason is desire to go beyond 2 ft lengths and have the ability to build devices with larger working area and, possibly, higher cutting forces - for example a 2'x4' router. The main problem here is getting enough rigidity for longer spans and higher forces.

After I got tired of slow and tedious process of making accurate perforated angle with the drilling contraption, I figured I'd do it with an inexpensive drill press.

Having made more than 8 ft of perforated angle on the drill press, I still was not completely satisified with the accuracy. This time the errors were mostly in centering of the holes. I guess aluminum angle jig that I made bent differently depending on the applied load, and so the holes were drilled in slightly different places. Oh well. It looked like a more rigid jig would fix this problem, or..

Having seen the massive bases for mini-mills and such, I knew intuitively that a light structure should not be able to produce very precise movements, especially when loaded. When I drilled 12 holes in a test piece and measured it with the tape, the error of almost -0.05" compounded over 1 ft. The distances between holes, measured with the caliper, were randomly off by +/- 0.01" - 0.02".

After going through the articles about accuracy and backlash on CNC Cookbook, I made a list of potential error contributors:

After I added the ENABLE control to both X and Z axes, it was time to calibrate the contraption. Besides centering the drill bit, there are basically 3 steps - a) determine which direction an axis goes when the axis direction pin is high or low, b) measure the distance between "all the way up" and "bit at the workpiece" positions, and c) determine the distance between the starting point on X axis (min switch) and the position of the first hole to be drilled.

Making centered, evenly spaced perforations in the aluminium angle stock turned out to be bigger challenge than I expected. Measuring and marking every perforation takes a lot of time, so I made a foot-long template out of 1" aluminium strip, with 12 perforations. I also made an angle template to mark the first hole in the other leg of the angle stock. These kind of worked, but the resulting perforations were still a bit off center and/or not exactly 1" apart. This resulted in alignment problems when I tried to build simple structures like boxes, specifically some holes did not match up by as much as 1/16" or even more, and/or some angles were not 90 degrees.