Holes larger at top than bottom

[rowbare]

It almost sounds like the cutter is flexing a bit. Try running the program 2 or 3 times on the same hole to see if it improves after each pass.

[ger21]

Originally Posted by rowbare It almost sounds like the cutter is flexing a bit. Try running the program 2 or 3 times on the same hole to see if it improves after each pass.

If the hole is too big on the first run, not sure how running it more will make it smaller?

[dertsap]

are you center or spot drilling the holes first ?

[Riceburner98]

Originally Posted by Ed Williams I can't find any play. I'm using a .125 bit. Holes are 20mm.

.125" bit cutting a 20mm hole, sounds like circular interpolation. (you are milling a 20mm hole with a .125" endmill, right?) If so, spot drilling isn't going to do anything for him. Only time I've seen this problem has been from cutter flex on a long-ish endmill, but then the top should be the correct size and the bottom should be *too small* in which case more finish passes would help... If it was flex it would have been happening all along at the same speeds / feeds. If all else is the same and it just started though, no idea....

[dertsap]

Originally Posted by Riceburner98 .125" bit cutting a 20mm hole, sounds like circular interpolation. ...

missed the 20 mmm

I agree cutter deflection ,

[rowbare]

Originally Posted by ger21 If the hole is too big on the first run, not sure how running it more will make it smaller?

It won't make it any smaller for sure but if the hole squares up, then you know that your cutter is deflecting and you can adjust accordingly.