So, I know I haven't been posting progress on my CNC machine build, but honestly most of the stuff I've been doing is wiring and tuning. That doesn't lend itself to a really exciting thread with lots of pictures. That said, it's been going pretty well and I haven't had to ask many more questions on the LinuxCNC forum to keep me going lately.
I have the X, Y and A axes under servo control and from my simple testing and setup I'm repeatable to within a few thousandths on each of the linear axes and many fractions of a degree better than I need to be with the rotary table. What I'm wondering from you guys is if you've come across or seen any good, methodical test procedures for initially validating a machine. Perhaps certain shapes and patterns to cut that test specific characteristics, or loops to check repeatability and such.
Just a heads up though before you suggest some awesome tests that will check within a few millionths reliably.... I do still have considerable mechanical issues that will be sorted out along the way. I know there's a ton of backlash in X and Y (probably on the order of 0.020 to 0.050 on a bad day), and a little bit in A. The Z axis, which I have yet to set up, suffers from being a worm drive rack with a clock spring counterbalance (like a drill press but with worm drive on the pinion). This isn't likely to change but I might tighten up the spring WAY in the future or maybe something else creative. All of this means I won't be taking heavy cuts that rely on the rigidity of the machine and anything that would test the machine's ability to cut in both directions at this stage is pointless. It will have to be treated as though it's an old worn out machine making cuts only when the backlash is taken up. I will be measuring the backlash and adding it as a parameter but I don't expect to have good results changing directions during a cut. I should get acceptable results changing directions and coming back into a cut though. I have future plans for anti-backlash nuts, or maybe ball screws if I'm so inclined.