Machine is making a wrong turn

[Sanderk]

So I bought a second hand CNC router and I am still learning a lot and running into a lot of problems and fixing them. But now I have a weird problem that I can't figure out.

When running a program the router suddenly takes a right turn where it is not supposed to. Basically it looks like it skips a part of the program and the X axis motor makes a grinding noise and then the machine continues with the rest of the program but it is now shifted ca 16mm in the X axis along with program and machine coordinates

- It does this only when running a longer program, I tried running only that part of the program where it happens but then it doesn't happen.
- It does it every time I run that program, within a few mm of the same spot.
- It does it regardless of the spindle cutting or running
- the machine is not doing anything difficult at that spot, it is just going in a straight line
- everything cut before and after is just fine except that it has shifted
- motor speeds and acceleration seem to make no difference

The tool path is made in Fusion and post is Mach3mill and I can't see anything funny in the G code but then I am no expert. The code is 8KB in total. I am running Mach3 on a Windows XP machine that came with the router. I don't know anything about the computer. It is connected to a Chinese board by parallel port.

The only thing I can think of at the moment is that this is a computer problem. Is that possible? I don't think it is a mechanical problem as it happens very repeatable.

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[difalkner]

Can you upload your Fusion file? Export it as an *.f3d file (you may need to zip it first).

[Sanderk]

The Fusion file is here: https://drive.google.com/file/d/1Rkp...ew?usp=sharing

Thanks for looking! I am open for any solution but it seems unlikely to me that it is the file. Can a program modify the zero point of the machine?

I have done some more investigation and from watching a video of what is happening I can see that Mach3 seems to run fine, it is not doing anything while the hiccup happens and when it gets to the next line of code it just executes that and everything else is in sync with running the program that has no hiccup.

Here is a video: https://drive.google.com/file/d/1491...ew?usp=sharing
It's supposed to cut the slot on the left but instead turn right too soon and the motor makes a funny noise.

So maybe it is the controller board? Or communications between the PC and the board?

[routalot]

I don't know if you have encountered Camotics,it is a simulation program that allows you to view the operation on your computer.As it is independent of the CAD/CAM system you have,it isn't linked to any other fault that the system may have.I suggest installing it-it is free-and watching the sequence very closely.If it executes correctly you should be looking at the machine and not concerning yourself with the software.It may just be a slightly loose connection somewhere or maybe some insulation on a cable has chafed and become a bit thin.I couldn't view any of the fusion files as I don't have fusion.Can you post perhaps half a dozen lines of the code at the point where the problem occurs?

[difalkner]

It's supposed to cut the slot on the left but instead turn right too soon and the motor makes a funny noise.

I guess I'm not understanding by your description "supposed to cut the slot on the left". The Fusion simulation looks right to me.

[bravernoe]

It sounds like your CNC router's issue during longer programs, where it unexpectedly shifts along the X-axis and produces a grinding noise, could stem from electrical interference, communication errors between Mach3 and your CNC controller via the parallel port, or potential software compatibility issues with Mach3 on an older Windows XP system. To troubleshoot, ensure all connections are secure, inspect for electrical interference, review Mach3 settings for timing and buffering, and consider testing with a different computer or upgrading your software setup to isolate and resolve the issue effectively.

[Sanderk]

In the video I am repeating the program without actually cutting and on the left you can see the slot already cut during the first 3 passes. It's only at the 4th pass that it suddenly goes off course and it does so every time I run the program. Yes, the Fusion simulation is right and also the path displayed in Mach3 looks right, there's nothing in the code that says it should do that.

[Sanderk]

It sounds like your CNC router's issue during longer programs, where it unexpectedly shifts along the X-axis and produces a grinding noise, could stem from electrical interference, communication errors between Mach3 and your CNC controller via the parallel port, or potential software compatibility issues with Mach3 on an older Windows XP system. To troubleshoot, ensure all connections are secure, inspect for electrical interference, review Mach3 settings for timing and buffering, and consider testing with a different computer or upgrading your software setup to isolate and resolve the issue effectively.

I guess I will have to do that. I already ordered a replacement board and if that doesn't work the computer is next. Electrical interference... I don't know, is that something that's so repeatable? I have run the program with only the X axis working, no spindle, no other axes and it still did the same thing at the same point in time.

[difalkner]

If it's at the same point each time then I would doubt electrical interference is the cause. Have you tried to run each contour profile separately?

[Sanderk]

Update: First I replaced the board with another one and still had the same problem at the same point. I then upgraded Mach3 to the latest version: didn't fix it either.
Then finally I replaced the whole PC with a new second hand one with a fresh installation of Windows 7 (comes with it own problems) and now the problem is gone.

Conclusion: not what the problem with the PC was, if it was hardware or other software installed but there was something weird in the PC.

[difalkner]

Update: First I replaced the board with another one and still had the same problem at the same point. I then upgraded Mach3 to the latest version: didn't fix it either.
Then finally I replaced the whole PC with a new second hand one with a fresh installation of Windows 7 (comes with it own problems) and now the problem is gone.

Conclusion: not what the problem with the PC was, if it was hardware or other software installed but there was something weird in the PC.

Glad you got it all worked out!