Problem with Z Axis creeping up

[HansM]

I bought the CNC router that Andrew (coldfusion) built and and I've been having lots of fun with it. I plan to use it mostly for wood. I'm using Mach2, SheetCAM and MeshCAM. I'm cutting 2-1/2 D with SheetCAM fine, but when I try to do full 3D with MeshCAM from one side of the cut to the other the Z Axis creeps up (see image).

Andrew said he did not have this problem so it must be something with my setup and not the mill. He sent me an .nc file from CNCone and I had the same problem with it so I do not think it is a MeshCAM issue. Andrew sent me his Mach2 XML config file and I'm using that.

Any suggestions on how to troubleshoot this or what the problem might be?

Lance

[HuFlungDung]

It could be a controller/motor issue.

Full 3d is different than 2.5d because 3 axis linear interpolation has to be performed by the controller. There will be many more Z movements in the 3d file. If for any reason there is a step being lost as the Z lifts up, this will accumulate over time.

[Cold Fusion]

The best thing to do would be to determine if it's a mechanical problem, or something on the electronics side. Take off the Z axis stepper and put a Sharpie mark on the shaft and motor casing. Then run a fairly long 3d program and see if those marks line up after it's all over.

[HansM]

Well, the good news is that it is electrical not mechanical. I tried the test Andrew suggested and the servo didn't return to zero. I expected this since I had disassembled the Z assembly to inspect it and and the ball joint, etc. were all rock solid.

So is it lost steps in one direction? What's the best way to pin down the exact cause?

Lance

[Cold Fusion]

I had a great idea today. It may be the high/low active option on the step or direction controls in Mach2. If these aren't setup the right way, you'll lose one step pulse every time the motor changes direction. I don't know how you have them set right now, but try changing them and running the program again. I know other people have had this exact problem, so this is probably the issue.

[HansM]

Going into Mach2...Config...Ports and Pins...Output Pins and reversing Z axis Step, Z axis Direction, or both caused the Z axis in my machine to creep down rather than up. This confirms that the issue is not with the machine itself but with the software.

Any other ideas?

Lance

[ger21]

Try increasing the pulse width and / or precharge.

[ger21]

That's Direction PreChange in Mach2, or Dir Pulse in Mach3. In the Motor Tuning window.

[Cold Fusion]

Yeah, try increasing them to about 3ms, instead of one.

[HansM]

The PulseWidth and PreChange were set to 1 and 0. I set they both to 3, then 5, and finially 10 and made cuts at each setting. No change in behavior. The axis creep was still there.

Lance

[Cold Fusion]

Just to clarify, you did try all 4 possibilties with the active high/low options?

[HansM]

Yes. I started with active low on for both step and direction. Then I tried turning active low off for just step, then just direction and finially both. The only change I saw was that the Z axis creep would change directions (up or down).

Lance