Pardon my ignorance, but I'm rather new to CNC. Maybe this is something obvious, but I haven't found mention of it yet.

I've just purchased a vintage 2000 Shopmaster/Shoptask Eldorado 2000 (ball screws, stepper CNC, DRO.) I'm having a heck of a time working out the backlash, but from what I hear that is typical (.002-.005 on all axis measurements.)

It seems to me that there is an obvious solution for backlash, as well as a good "hint" for limit and home positions: the DRO. It seems obvious that the DRO actually "knows" where the X, Y, and Z positions are, regardless of how far the steppers are spinning. Why isn't it more common for the DRO to relay this information back to the computer head-end? It's a pretty obvious solution, but in the last few weeks of digging through this (and other) archives, I've never seen it mentioned. None of the CNC software that I've demo'ed (FlashCut, Mach 3) seems to have any provision for DRO feedback. The DRO I'm using looks like it has a spot on the bottom that is a DB-9 -shaped cutout, but there doesn't appear to actually be a serial feed.

Wouldn't this solve a huge number of headaches if the controller actually knew the real distances the steppers were driving the axis movements?

- backlash avoided
- blockage or collisions detected
- inaccurate stepper software configurations detected
- manual adjustment compensation reflected on controller
- more?

JT