Circles on profile pass

[PNast]

Does anyone know what could be causing these full circles when it ramps around the profile pass? I have a PRSalpha 96-48, HSD 2.2HP Spindle. I am using an Onsrud 60-242 1/4" Solid Carbide Three Flute Downcut Low Helix Finisher. I have also tried the upcut one too. It happens with all different types of wood. I have tried different speeds 2 ips - 4 ips and chiploads between .004 - .007. The pocket depth is .125 and it even happens if I run the file again at .005 deeper. I am using a new bit and collet that I just got yesterday.
Thanks,
Paul

[steve_g]

Paul…
I’m just guessing here… It appears that the divots are always at a change in direction… is anything loose that would shift at direction change?
SG

[Brady Watson]

Sometimes backlash in the Z pinion to rack is the culprit. Power up and shake the Z up & down. Also, on PRT check Z v-roller to t-rail play. On PRS check YZ bottom v-rollers. Grab and shake it all down. Listen & feel for play.

-B

[dlcw]

Another possibility is that your material is flexing up and down. Doesn't take much.

[PNast]

Thanks for all the help! I checked the bottom YZ rollers and one was loose enough that I could spin it by hand. After getting it all locked down, I cut a sign and the circles are still there. All the motors move a tiny bit but I was told that is normal. The front X motor moves a bit more then the others. I had Nate from Shopbot come to my shop to help figure out why it was cutting deeper on the profile pass and square up my gantry. He said the X motors had some backlash, he took them apart but I don't think he was able to adjust them. I just pulled the sign and looked under the lights and the circles are definitely not as bad. They seem to be only around the curved areas where it moves in the X and Y at the same time.