Digitizing with Alpha

[stevem]

Has anyone here done any digitizing of 3D objects using the Alpha Bot or a Bot upgraded to Alpha or a Bot with steppers that do not have gear boxes? What accuracy were you able to achieve? What about accuracy with steppers and gearboxes?

I am trying to determine the expected accuracy of measuring large parts with a probe mounted in the router collet.

Thanks

Steve

[ron brown]

A lot of that accuracy would depend on how well the machine was setup, more than any other factor, IMO.

Ron

[jesummers]

We were doing just that, first using time borrowed on a PRT and then on our own PRT Alpha. I can't comment directly on the difference in accuracy because the PRT had various problems that came to light just before our new Alpha was up and running.

I never got around to doing a full calibration of the touch-trigger probe setup but suffice it to say that it is hard to characterize. There is the positional accuracy of the machine, overshoot of the z axis after contact (which depends on the move speed and the weight of the carriage), asymmetry in the probe response, repeatability of the probe, and, especially, the accuracy of the machine setup.

That said, I think the Alpha is at least as accurate as the original PRT for this task. The positional accuracy of the old PRT was 0.254mm and the positional accuracy of the PRT Alpha is 0.127mm. I'd estimate that in a real-world scenario on an Alpha +/-0.25mm is a fair estimate of the accuracy.