Every part I cut gets progressively larger around the diameter of the cut as it cuts deeper. It never mattered to me before, because I was just cutting decorative stuff. But now I am trying to cut a new router mount that needs perfect 90 degree angles, and I just can’t cut them. It isnt a calibration issue it seems, since it gets larger in every direction. Here are some pictures of the mount I cut out of UHMW for reference. It shows the part in Easel, then a top view. Then four different sides.
What size bit? How fast? Could it be bit deflection?
On this I used a 1/4 inch two flute straight. About 30 inches per minute, 2mm depth per pass. Bit only extending 3/4" from collet. 10mm material. I get the same results with a single flute 1/4 and upcut two flute.
Could it be deflection from the aggressive depth? Maybe I should recut with maybe 25% the depth? My router nor nema 17 steppers struggle cutting this. No apparent messed steps. I notice this too when making shallow cuts into aluminum. I cut some .06 inch aluminum and get the same results at .006 per pass.
My machine is rock solid. All of the rails are reinforced. Z axis wheels are right against the rail. No movement in the router mount. I’m changing routers because my Harbor Freight router has excessive runout since I had a bit come out while cutting. The back of the bit cut a groove into the collet. I just went through and squared up the machine to within about .003" in all directions.
I plan to fix the back of the new router mounts with my router table to get the new router mounted before I attempt to cut again. I guess it could be an interference issue with the HF router. Or even the speed controller?
Agreed, cautious almost for that bit.
What happens if you run the job twice? Does it clean up the edges or follow them?
Ive never tried running a project over. I will try that and see what happens. This UHMW is expensive, so I’ll try on some MDF 
Looks like your material “walked” away while cutting, it is quite slippery material so is your clamp rigid enough?
UHMW I think
I don’t think it is a walking issue, since it is in every direction. It happens with wood that is screwed down too.
I was able to flatten the back of the mount and temporarily mount the Dewalt. I then recut the part and they came out great. No changes but the router itself. Maybe the HF router was making noise affecting the controller?
Glad you got it nailed down.
I have had this machine for a long time, but little issues made it just sit in the garage. Only now I am trying to get it ironed out so I can use it. If I can make it reliable I plan to upgrade it to 1000x1000 format.
You mention that being a harbor freight router. I’d be willing to bet that a lot of that is runout. I tried using one cause what the hell $19.99 right. Between both radial an axial runout it was almost .032 in. on a short end mill. That’s right a 1/32nd of an inch. I thought I had the collet installed wrong, nope. Basically don’t wast your time with them. I’ve heard of people getting “good” ones. Just not my experience.
I don’t think that was noise affecting the controller/steppers. I’d say that was play in the bit from the router being cheap and that groove you mentioned.
Glad you got it sorted.
