Official Luthiers Forum!

Hello everyone.

I am having an issue with my CNC. I was running a guitar body today and after completing the two humbucker routes, the CNC started the neck pocket 1" too far to the right (I stopped the machine before major damage was done). I have only had this problem once before. I was cutting out a headstock shape and the CNC was too far in the Y+ axis. It never seems to happen to any other AXIS.

Machine Specifics:
Mach 3 (latest version)
Techno Isel 040 H830 with stepper motors

If I remember correctly, the first time I had this issue the CNC had been running all day. This was the case this time as well. I felt the stepper motors today and they were quite warm to the touch. The controller felt warm as well (not as hot as the steppers).

I also noticed in Mach 3 status bar it said: Scripter compile error:In:M3.m1s (I have no clue what this means)

What do you guys think is happening here?

Did you re-check your zero reference after the anomaly? I have had instances where the motor lost pulses and went out of calibration.

I don't trust anything without encoders on a CNC (but I've run closed loop steppers), but I've seen this enough on one of our 3D printers. Sounds like lost steps or lost zero, easy enough to test which. If the program is not new, has worked in the past, and you haven't changed your control parameters, then it's definitely lost motion of some sort.

Lost motion can be electrical/steps (one of our motors would just heat up over time and lose them in the middle of a long print), or mechanical (we had another where the coupling would slip sometimes due to a loose set screw that hadn't been thread-locked). Check everything in the transmission first to see if you can get a quick fix. Otherwise, it's science time

Diagnoses:

Lost Zero: Run the program with all the Z moves taken out, from the start, with a pause at that point. Two or three times. At half feed rate. See if it still happens.

Lost Motion: Run the program with all the Z moves taken out, from the start, with a pause at that point. Two or three times. At increasing feed rate, from normal to crazy. See if it still happens.

You can quickly test for motion issues just by jogging it back and forth on the relevant axis hard a few times (rapid back and forth) to see if it loses position, but it might not reveal electrical issues.

Good luck!

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I've had similar problems in the past when running really large programs with Mach 3. Basically, if the computer is on the slower side, overhead can mess up the timing signal from the parallel port. When this happens, the steppers lose torque and miss steps. The funny thing is that the timing errors can occur pretty much anywhere in the program, not necessarily only late in the program.

A couple of things that can help:

1) Turn off the toolpath preview area
2) Run the program from the local hard drive
3) Break the program up into smaller chunks
4) add a hardware pulse generator such as smooth stepper or Kflop
5) migrate from Mach 3 to a controller that sucks less.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I would be interested in a different controller if it comes to that. Andy, what do you suggest? Why did you leave Mach 3?

Alexander,

Unfortunately, I haven't switched from Mach 3....YET! I've bought a Kflop and just about everything I need to get it up and running (except encoders as I'd like to move this machine to closed loop steppers) but I just haven't made enough time yet to do the switch. Bob has pretty much convinced me that as far as non-multi-k$ systems go, the Kflop is the way to go.

Why do I want to leave Mach 3? Simple - it's way too expensive to operate. All of the tips I included in my earlier e-mail are things I learned after destroying parts using Mach 3. There's a lot of bugs in Mach 3 and I'm just sick and tired of finding them on customer parts.

As you probably already know, most errors in CNC work can be traced back to errors in programming. I definitely have my fair share of those, possibly even more than my 'fair share'. However, you'd expect that your controller software would be pretty rock solid and do what you're telling it to do. Well, Mach 3 does what you tell it to do probably about 95% of the time. In my case, the 5% it doesn't behave as commanded is costing me money.

Because of my time issues, I may investigate throwing on a smooth stepper temporarily in the hopes that it will help some of the reliability problems I'm having. I have a friend that builds machines for sale and he uses the smooth stepper successfully. He'll loan me one indefinitely so it's a low risk proposition. Ultimately I'd like to get switched over to Kflop/KmotionCNC for my controller.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com