X position changing during cut

I’ve recently put a new x-axis belt on and calibrated.

During my last two project cuts, I notice the x-axis was off by an estimated -2mm at the end of the cut. I’m a bit at a lost, what do I adjust or change to address the x-axis moving during a cut. Belts are tight, matter of fact x-axis is a new belt. x-axis wheel is clean. Calibrated when I put the new belt in. What am I missing?

The project - I’m cutting Baltic plywood with 1/8th combo bits cutting 0.125" per cut at 30 inches/min.

There have been suggestions to measure your actual bit diameter; not all bits are equal.

Hmm, true not all bits are actual bit diameter. My 0.125bit measures 0.122in

I’m using Triquetra to zero my bit at the start of every cut.
I should have noted, I know x-axis is off because I return to Zero and well it’s not zero anymore. It’s off by roughly 2mm

I’m not understanding how the slightly smaller bit which is zero’d returns -2mm after the cuts. I’ll note, this happen 2x

It might be worth trying your calibration again. It is suggested to use a vbit for referencing the measurements. This might be how you are doing it already. And check wheels for proper tightness too.

Is it consistently off by 2mm?

If I am I reading that correctly you are using an 1/8" bit but talking a 1/8" Depth Of Cut. If that is the case you maybe overloading and causing it to miss steps. The rule of thumb is the DOC should be 1/2 the bit diameter. So in your case the maximum DOC should be .0625. I realize 30 ipm is on the low side but still that is a hefty cut for an 1/8" bit. I usually start at a DOC of .05 with a 50 ipm speed. If cutting seems to be going well I start pushing up the speed with the real time controls until I start getting chatter of the quality of the cut declines.

When I replaced my x-axis belt, I cleaned and tighten all wheels.
I just did another calibration.
Did another cut and this time it is off 2mm on the x-axis and y-axis.
I’m going to go with @RayMacke suggestion and decrease the DOC. I was going slow on the ipm because I was going 0.125. I’ll give the 0.625 and 50ipm and see what I get. Perhaps because I’m cutting gears with fine teeth, I might be causing overloading and causing miss steps. So close the cuts look good but with the miss steps the gears are not centered. Seeing these are for a Wooden Clock I might have a problem. Best to figure it out…

Is this feed and speed something that worked before the upgrade? Or you were trying something new ?

Didn’t really work well before, I’ve been having too much play in my Z-axis, which is in part why I upgraded my Z-axis to one of the CNC4Newbies. Now I have no Z-axis issues, and not getting chatter. Without chatter I wonder if I’m not noticing some overload. Didn’t really think Baltic plywood at 0.125DOC would be an issue at 30 ipm.

Cuts are really nice - just need to address the miss step issue and I’m golden.
Running a new cut at 55 ipm and 0.0625 DOC this morning.

I did a test yesterday. I ran a file to my CNC with the bit above the wood, hence not cutting a thing. File ran about 1hr 30min. I had my 60-degree v-bit in my router so I had a point to measure. I Zero’d and marked my base with the point. Than moved Z-axis a couple inches above the wood so it didn’t touch a thing during the run.

When the file was done the v-bit was -1.1mm off on the X-axis from when it started with no cutting. This is about the same as when cutting. Figured this was a better test than running more feed and speed test.

Any suggestion what I need to adjust to keep my system in line? I don’t expect the Zero should be different from start to finish.

Gshield or Xcontroller?


I should note, the file is set to 50in/min.
Any suggestions?

Follow up on this issue - I believe I finally figured this problem out. While troubleshooting, I discovered that my X-axis pulley wheel was missing a set screw and the second one was loose… Argggggg. Ran a test last night of a fairly complex gear file with the bit above the wood, hence a no-cut run. And X-axis returned to the same zero spot as before the file. Before this same file was off -1-2mm… Go figure.