Originally Posted by BobWarfield  Of course that's not really true for many of the lower end ballscrews where the error rates can be several thousandths over a foot.
I'm surprised at you Ray, you silly goose! After chiding me for essentially mapping mine over a short distance because you thought the errors could be much greater over a longer distance you're now going to swing way over to the other side and insist this only matters to a temperature controlled shop?
I certainly found enough error over the 6" I measured that it was a valuable exercise, though I accounted for it in the steps per inch setting rather than in the leadscrew map.
To answer the question of how, you use the DRO to compile the actual position at various points as you jog over the full distance of travel. Take a measurement at 1" intervals or whatever. Record two columns in a spreadsheet. One column is what the Mach3 DRO says, the other is what your external DRO says.
There is a screen in Mach3 where you then enter these values. Mach3 will interpolate in between to eliminate the leadscrew errors. Art has said it works pretty well.
I got a screamin deal on a new Fagor DRO that I plan to use for exactly this purpose.
Cheers,
BW |
Aw, come on, Bob! It's fun! Actually, I never really looked in any detail at the magnitude of thermal expansion on these things. Unless I've slipped a digit somewhere, it's a lot less than I had assumed. The coefficient for steel as roughly 12 x 10-6, which, over the working length of a Bridgeport table (about 34") amounts to less than 0.0004". Not bad. Now, the amusing thing is, the glass scales will themselves experience about 2/3 of that. So, I think we need to get some diamond scales.... :-)
Are your new scales actually glass? Or Mylar? I would expect Mylar scales to vary pretty widely.
I would be very curious to see what the variance is over the length of a long screw, to finish off the discussion last week re: screw accuracy, and lead consistency.
Regards,
Ray L.