We were doing a training session this evening on a 1100 Series 3, cutting a small pocket in an aluminum block with a 3/16” endmill. The feed had been reduced to around 25% just for demo purposes. All of a sudden, the spindle speed dropped to almost nothing and the machine continued to drag the bit across the material. The program had been done in the conversation tab and was solely a 1/2” x 2” slot, 0.2” deep. The problem began in the first pass through the material.
We stopped the program, retracted the head and watched the spindle. Without any input or touching the machine or the head moving in any direction, it would go back up to speed and drop off to 1-2 RPM. There wasn’t any change in the data on the screen. It is as if the machine had a mind of its own. Almost like someone turned off the motor and then it came back on.
We switched over to manual spindle control and it runs just fine. Tried redoing the program and starting over and it ran fine for a while and then would begin to act up again so we don’t think it is a program or G-Code issue.
Never seen this type of problem before so I don’t know where to begin to look as to where the problem is .
Any suggestions or help would be appreciated. We are solely hobbyists, using a community machine in a Makerspace. We are the only ones who use the equipment so it’s hard to point the finger at the other guy.
I would start at the VFD and make sure all the wiring connections are secure. While I’m not sure exactly what the comms protocol is, there’s the potential that if an input wire (or ground or V+ for that matter) has come slightly loose, that could cause the sort of intermittent issue you’re seeing.
The series 3 doesn’t have a spindle encoder so it doesn’t really know how fast the spindle is turning, only how fast it told the VFD to go. Similar in that regards to the stepper drive. The machine knows where it’s told the steppers to go, not where they are. Anything that happens between the controller and the output motor in both cases, doesn’t get fed back into PP.
Checking all the connections, everything appears good. When the issue arises, it appears the speed reductions are being commanded by the VFD. I made a video of the controller flashes and also the VFD readout but don’t think a video can be posted to this forum. I’ve added it to my personal site and linked it from here. Click on the title below to run the video,
You can hear what we believe is multiple: Tock-Tock-Tic repeating
The readout on the VFD varies from 0 to 2.3 to 0 to 3.3 to 9.4 to 0 which the spindle rotation is matching. The speed is set to 5000 rpm which typically shows a number around 549 on the VFD as I recall
The system runs fine in manual mode.
We have tried multiple programs to verify it isn’t a programming error - it seems the speed command from the computer is varying and the controller is following that command.
Early ATC boards had mechanical relays on them that could vibrate open and stop the spindle. That usually involved a lot of chatter from the cut, but could be related. I’d talk to Tormach support.