Problem- 1993 4020 VMC Y Axis

[Linear360]

Our 4020 VMC has a problem on the Y Axis. The centerline location of holes is reading a .025 difference between the drawing and actual product. I have checked the program and the file it was written from and they are consistent with the drawing. I dont believe it is the fixture offset because both hole locations are taken from the same datum and the difference is between holes. Any suggestions?

[Delw]

did you indicate the part in before you ran it?

did the part move when you were running it?

did you indicate the part in after you ran it?

are you using raw uncut stock?

so many possibilties, just need specifics

[little bubba]

I have $10 that says when you find the problem your going to feel like an idiot (we've all been there and done that, no shame in it, it happens, they are "learning experiences"). I'm also going to bet that it isn't machine related.

I'll even go so far as guessing that your vise or fixture isn't square, or you have a bad # in your program.

Question, how are you measuring the hole location and is the datum already machined before the operation or machined during the operation??

On edit, are the holes at the same X location??

[SORCHEROR]

how far apart are the holes?.025 could be a bad spot in the ballscrew,or the screw is worn so much per inch and the holes are far apart,did y check backlash ,would give an idea of worn screws
also,how are u checking the holes?

[scadvice]

little bubba is right....just when you think you've seen it all....
Steve

[Linear360]

youre right, the material isnt square, but how does that matter when the difference is between holes? the holes should still be an inch apart from the CL, regardless, and they are good on the X axis.
how do i check the backlash?