Looks like the 5-axis idea is out of the question. The site I was using to get a quote has an idiosyncrasy that can make you think you're getting the price for machined 6061 aluminum, when you're actually getting the price for sintered nylon. 5-axis machining is too expensive for this, for the time being. I'll look into other options later this year.
The old design uses captive nylon locknuts to hold the joints in place. I think I mentioned above that this makes it very difficult to print properly on a resin (SLA) printer. Since I had to redesign the effector in Fusion 360, and since Fusion 360 has the ability to cut accurate threads directly into the model, I decided to drop the locknut idea and just thread the holes the ball joints screw into.
I finished printing a prototype on the Form 2 earlier today. The threads printed a little tight, so I had to use an M3 tap to clean out the first few millimeters, but the ball joint screws went in just fine. The tightness of the threading gives the screws something to bite into, just like the locknuts did before. Having the whole length of the holes threaded also makes it easier to calibrate all the ball joints to be at the same elevation.
This is the result. The threads printed beautifully, and I don't have to use locknuts to secure the probe mount anymore.
I mounted the new calibrated effector to my printer, and ran my heuristic calibration routine. Average Z error is 34 microns, or 0.0013 inches! This is the best calibration I've ever seen on this printer.
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[PD] 0.069
[PD]
[PD] [ -- ] -0.006 0.056 0.019 -0.013 -0.025 [ -- ]
[PD]
[PD] [ -- ] -0.013 -0.006 0.000 -0.019 -0.013 [ -- ]
[PD]
[PD] -0.087 0.019 0.006 0.000 -0.019 0.025 0.050
[PD]
[PD] [ -- ] 0.025 -0.006 -0.019 -0.013 0.006 [ -- ]
[PD]
[PD] [ -- ] 0.050 -0.013 -0.013 -0.013 0.019 [ -- ]
[PD]
[PD] -0.081
[PD]
[PD] Best=0.000, worst=0.087, min=-0.087, max=0.069, mu=-0.000, RMS=0.026, sigma=0.026, energy=0.034
I'm still using the old carriages, which have nylon locknuts. I might redo them in Fusion 360, giving them the same printed-in threads and ditching the locknuts.
If I can get these good enough, and if they make it through beta testing, I'll sell them.