PM25mv, how to sort out X axis discrepancy between DRO and handwheel

burtonbr said:
I’d think that it being stiffer at the ends for travel is more gib getting tighter than lead screw issue. If it is repeatable within tenths over 6” or more inches that would be acceptable for most work for that mill I’d think. Acme lead screw with brass nut and not a ball screw if the DRO os holding true that’s pretty good.
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Thanks a lot... I can live with it, as the dro seems accurate and repeatability is fine. Just a case of a slightly out of standard lead screw--50-60 degrees F thermal difference in the factory would be all it would take to create the error I'm seeing.

Thanks for you help everyone, I'll probably contact PM to see what they say--maybe they're aware of a bad batch.
 
Mine is the same way, ill never be making parts 15" long so i dont worry about it. My table also gets stiff at the one end on both axis, i have the gibs adjusted alittle looser than i like but i can hold +- .001 pretty easily. If i need more accuracy or i find myself doing longer work ill get a dro. My main problem is the head nod, i have .0045 from the far extremes of the table front to back, but it stays at .002 over the width of the table, if i need closer ill just shim the vise. Alot easier than other mods ive seen done.
 
I didn’t think being off .011” after 27” of travel was that bad, that an average of.0004”/inch, unless the error happens all at once. Beside I thought the object of a DRO was so you did not have to use the dials again, using the dials along with the DRO seems counter-intuitive.
 
My z axis handwheel has error in aswell, i just use the dro and use it for reference.
 
You shouldnt use the handwheels to verify the accuracy or inaccuracy of the DRO. Depending on the DRO, you should easily be able to hold a 2 or 3 thou accuracy over your travel. The only way to properly measure this would be with a known standard or lasing it. Without either of those, the next best thing I use when checking accuracy would be the long side of a 123 block.

Jon
 
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