Pocket cutting issue

I’m having an issue with cutting pockets with my Shapeoko XXL. I’m trying to cut 2 1/4" diameter by 1 3/8 deep pockets in 1 3/4" thick mahogany which are used as cup holders in tabletops. I’m using my .250 end mill with each pass cutting .090. The problem is that the pocket will cut down to .750 deep, come back to the plunge location, lift up about 1/4", step over slightly ( 1/32")into the pocket wall, then seem to loose communication, move to the center of the pocket as if to start another pass and plunge completely down through my work.
I’ve been dealing with this for quite a while. Carbide 3D support has suggested many things such as checking for EMI, tightening my Z belt, using new, sharp bits, using a .250 bit with 1 1/4" long flutes, all of which I have done with no success. I’ve experimented with many different combinations of feed and speed rates.
I can cut multiple 1/4" circles ( contours) 1 3/8" deep with no problem but when I try a pocket, the problem happens. The bit heating and warping issue has come up but I don’t feel that this is the issue. I would think that cutting 8 consecutive 1/4 circles would heat the bit more than 1 pocket, yet I have no problems cutting these circles.
I’ve tried the same pocket file in styrofoam with no problem. I realize I’m getting more resistance in the mahogany but the fact that every pocket screws up at exatcly 3/4" deep has me baffled. I’ve gotten to know which pass its going to happen on as every pocket has screwed up at the exact same spot in the operation.
I recently “threw in the towel” and made a jig for my plunge router out of 3/4" mdf and have been cutting my pockets with that. Maybe the Shapeoko just isn’t capable of this operation??

Hi Paul,

It really sounds like a mechanical issue,that may or may not be made worse if feeds and speeds are suboptimal (which you hint at when saying that the bit is heating and warping)

  • how did you address the Z belt recommandation from support ? are you positive that your Z belt is now tight enough?
  • are you X/Z plate V wheel eccentric nuts tight against the X rail ?
  • any chance the bit might be slipping in the collet ?
  • can you please share your feeds and speeds (RPM, feedrate, plunge rate that you use for that 0.09" depth of cut?)
  • is there any weird sound/rattling happening at the time this happens ?
  • can you share your G-code for a quick double-check ? (probably useless, if its runs fine in styrofoam)

The Shapeoko is definitely capable of this, and (much) more, but sometimes a tiny setup issue can get in the way.

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