I know there have already been a few threads about this, but I’m adding another in hopes that Onefinity will take a closer look. I’m having persistent problems with round pocket accuracy, and at this point I’m fairly certain it’s not a toolpath or setup issue.
The issue:
I was cutting a simple challenge coin pocket today—a 0.75" diameter round pocket at 0.15" depth. No matter what I do, the pocket consistently comes out undersized.
I’ve tested just about every variable I can think of, including:
Climb vs. conventional cutting
Offset vs. raster pocketing
Multiple passes and varied cutting strategies
I’m roughing with a 0.25" end mill, and the result is always the same. The coin only fits if I draw the pocket as 0.91" instead of 0.75", which obviously shouldn’t be necessary.
At this point, nothing I change in the toolpaths makes any difference. This feels like a systemic round-pocket accuracy issue, not a CAM strategy problem.
For clarification, I have:
Measured the bit diameter with a micrometer
Verified the correct bit diameter in the software/tool database
Confirmed it’s a pocket toolpath (so no “inside/outside vector” confusion)
A consistent maintenance routine as recommended by Onefinity
Never needed to tram the machine before
Never calibrated X/Y via MDI (didn’t know that was a thing)
Not calibrated X/Y in general
Noticed this issue starting around June after a firmware update (approx. two updates ago)
Is anyone else seeing this behavior, or can Onefinity explain what might be causing such a large dimensional error?
You mentioned all the things you have tried, but unless I missed it, I did not see you list your depth of cut, feeds and speed. If you are running a roughing pass, do you have extra clearances added? Have you tried running the same file with a finishing pass? Does the problem happen consistently everywhere on the table? What happens if you use a very slow feed, with a very slow depth of cut? Have you measured for back lash? With the machine powered on, your steppers should be locked, and your router or spindle unplugged, move your machine to center position and the z as low as it can go, take the collet nut off and grab the threads, and with reasonable force you should get no movement…if you are seeing movement you have a mechanical issue. I am not saying that you are wrong, but in my experience over the last 20 years of being a hobby cnc guy (I don’t do this for a living and never have), I don’t recall a time that it was software, unless I had incorrect settings or using too much feed/speed for my machine. CNC machines are great at masking problems and making random errors seem consistent. My guess is you have a mechanical problem, usually something loose or binding. Sorry I know how frustrating it can be when you are at a loss. Doing routine maintenance might not help you find some loose nuts or bolts that don’t readily show up from visual inspection. Good luck, you will find it. I think you are on the wrong track looking at CAD, CAM or Controller issues, especially if you are 2 updates past when you started seeing it.