Step-down cuts are on a different path?

Hi, hopefully I can explain what’s going on clear enough and someone can help me out. I’ve been using my Pro 4x8 for almost two years (as a hobbyist) with pretty decent success. Yesterday I started cutting out pieces for a workbench, the first pass seemed fine but when it stepped down to make the second pass it no longer cut on the same path. I stopped the file, salvaged what I could, set up a new g-code/tool path in fusion 360 and cut out some pieces individually with no problem. Later I cut out two larger pieces at the same time with no issue. This morning I went back and tried to cut four small pieces out and the same issue arose, second layer was off, and the third layer was off as well. I’ll try to upload some pictures to help explain.

I did something like this one time. My mistake was not paying attention to setting xyz I had entered the wrong diameter bit. Your issue might be different but looks like the one I had.

Determine if it is all happening on the same axis, also first thing I would do is drop my steppers and manually move the axis to see if there is any binding, during this process I would also check for anything that has come loose by first unplugging my spindle, then grabbed the collet and shaking it in every direction. It’s most likely mechanical. If you can’t find anything mechanical my next suspect would be stepper drivers.

Looks too consistent to be a mechanical error. But I am doing the 5 seconds eyeballing thing on a photo that I have no reference of what was the intended outcome.

Same file makes same mistake? Or does the same mistake happen sporadically, different files?

Thanks for the feedback Cliff. I thought it might be that as well but I double checked the bit size. Everything seems like it’s been entered correctly.

Thanks Erik, I have had the issue on the x and the y axis on two different setups.

thanks Subnoize, I agree with you, it doesn’t seem mechanical to me, the machine seems to move fine, it’s solid, no weird noises, the cuts are consistent just on the wrong path. It was supposed to cut simple rectangular strips, no rabbets.

Different file, same mistake but on a different axis. I’m in a support email thread with Avid hopefully we can figure something out. I’m out of town for a few days so I won’t be able to work on it until next week.

I don’t know how to read g-code but I’d like to figure out if it’s correct or not.

Different tool path types will place the cutter on different sides of the path being cut.

There is even a switch in some CAM packages that will select which side of the tool path to place the cutter.

In your CAM package, do a simulation and see if you see the same results. This looks suspiciously “perfect” which is my clue that it might be “pilot error” in the CAM.

I agree that it looks too “perfect”. my cad/cam is on Fusion360 and when I simulate the cuts they look correct.
(your dust collector and bit changer on your cnc look sweet)

One thing that happened that might be a clue is when it finished cutting and returned to its “home” position, it tripped the limit switch and disabled itself. It’s done that in the past, not sure why and not every time.

Ah! You are losing steps. You are either exceeding the cutting capacity of the end mill or you have a bad pinion gear on that axis.

A thing to remember is the speeds and feeds published most often are for the diameter of the tool in depth. So if its a 0.25" tool then that feed rate is at the depth of 0.25".

Tool manufacturers like Amana will put a little note that you reduce the feed rate by 25% for each diameter of the tool in depth. So if you are 0.25" diameter then 0.26" to 0.50" you reduce the feed rate by 25%. 0.5" to 0.75" is half the published speed.

thank you, I’ll definitely look in to that when I get home!

You should just run the g code without cutting. Pause the code when the cut has been going wide and not following the previous cut. Will eliminate gcode issues from mechanical issues.

So just quick update, I haven’t had time to work on the issue yet but I will hopefully today or tomorrow.

So I ran an air pass (not sure if that’s the right term) it was running correct until it stopped mid run and I got a message saying “Lost communication with the ESS board”. I updated my mach 4 software ( I was running a very old version) and ran the Windows Performance Tuning Routine. I ran another air pass and everything looks okay. So, I don’t know if it was just a communication error with the ESS or if I was exceeding the cutting capacity or if it’s something else. I’m cutting 18mm birch with a 3/8 compression bit at 200 IPM with a .3" step-down and 17,000 rpms. It is a little faster and deeper than I normally cut but I didn’t think it was that aggressive. (4 hp spindle) I’m going to go over my CAM again, maybe back everything off a bit and see what happens.

Thank you for all of the feedback/suggestions everyone! It’s nice to have this community, I’m very grateful.