Surfacing Anomaly

[RhoTu]

I am at a loss to explain what could cause this. I noticed that I was getting lines at each successive depth on one side of the pieces being cut. I thought my spoil board may have warped so I started to resurface the spoil board and noticed that the Z axis was not aligned with the Y axis so I spent a few too many hours tramming the the Z for both x and y so that my surface came out as smooth as I could get it whether surfacing in the x or y direction. Great.

Then I put a dial indicator on the spindle and when I ran the Y axis there was a .010" difference over a 7" in space!!! That can't happen can it? I mean even if the Y axis was tilted the surfacing bit would follow the tilt and the distance to the spoil board would remain constant, right?

I ran an 8x8 test on a board screwed to the base, ran a 1.375 surfacing bit first in the x direction, same slope in the Y. Then ran another surfacing done in the Y direction, same slope in the Y. These were ran at 20 ipm and 15000 rpm to make sure that there was no rigidity issues. I have been able to verify that the Z screw is not moving during surfacing nor is the bit moving in the collet.

Can anyone explain where my logic is failing?

[4DThinker]

I had a student Friday cutting a row of pockets for a finger joint. Although all the pockets were created to cut the same depth only a couple of them were even close and none were exactly what they should have been.

What could have caused this? Turned out it was a loose bit. Bit was slipping in the collet.

What caused your .01 error over 7"? The material may have warped after it was cut.