I am working of a 19"x48" sign. I needed to pocket .2" around a few rectangles. I used a 1/4" downcut bit at 0.05" per pass. The job was to take 2 hours - which was okay with me. I started the job and everything looked fine and steady. After about 1.5 hours I saw that things were still looking good. I expected it to be finished in about 30 minutes. However, suddenly the machine (Shapeoko 5 Pro, with 65mm spindle) reacted as though the job was finished and parked the spindle. I looked at the project, and it was far from complete, with much left to be cut out and irregularities all over the place. I had not noticed any interruptions during the job. I decided to restart the job and noticed that when the bit landed on Bitsetter, it did so way off its center (Usually it lands dead on center.). From experience, I know that when this happens (after some kind of jolt to the machine) to restart the machine as well as carbide motion. I did so and restarted the job, this time at 0.1" depth per pass. The job completed this time and fixed the irregularities on the board from the previous go-around.
So, my conclusion is that the machine software somehow got confused during the job, for some unknown reason (It did not get jolted during the job.). Has anyone experienced something like this or do you have a theory what happened? Thanks. - NDL
This kind of behavior is usually due to lost steps either from mechanical binding/blockage or poor wiring harness connections.
The G-code just tells the machine the path to follow. The controller steps out the motors to achieve the desired path but it has no feedback if a motor has actually moved correctly with each step - it’s open-loop control. And for the most part for these small CNC’s it works fine - until it inexplicably doesn’t.
So check your mechanicals & wiring connections - make sure the connectors are secured tightly together & not getting pulled/strained while the machine moves around. This is usually an issue on the X/Z motors since those connectors are moving around with the spindle.
Lost steps would shift the remainder of the toolpath in the opposite direction of the lost steps.
In this case it sounds like the toolpath didn’t finish. This is usually some kind of signal interruption, either EM interference or a loss of communication. It could also be the software (CM) hiccuped and stopped sending data. Tough to troubleshoot. Make sure your USB/Serial comm to the machine is solid.