Problem- Y axis drifting

[Realmseeker]

Good day all,

I have been trying out the CNC for the first time over the last few weeks. I Have it actually doing some of the basic wizards built into Mach3 just to get a feel for what I can do as I learn more Cad/Cam stuff. I tried the circle wizard just fine, but the Rectangle pocket ones and other shapes are causing me a few problems.

When I set it to cut a rectangular pocket, the y-axis drifts negative after each successive plunge. As you can see in the pic, it looks like a bunch of steps. The X and Z seem to be doing fine. The good news is that the bottom edge to the far edge measures the correct width.

I tried playing with all the CV settings. Tried changing the pulse and steps up to 4(maybe try 5?), up the frequency from 25k, to 35 and 45. Also I tried using the backlash settings and shuttle settings, and that only made the steps worse. I also tried CV mode and Exact stop.

The work piece isn't shifting.

To see if it was a mechanical problem I switched the pin settings for the x and y axis and the 'steps' also switched sides. So I believe this to not be a mechanical problem, but a software setup thing.

Mostly I was trying 2"x1" pockets, 1/8 to 1/4 inch deep and going in 1/16 step depths. I have also tried this on 2x2 and 3x3 pockets all with the steps showing up on the same side and getting bigger as the pocket gets bigger.

The system is:
G540 gecko
48V Meanwell PSU
300oz or so steppers
Mach3
Spindle: laminate trimmer(securely held, and not shifting in the holder)

So please any suggestions on what I have missed would be helpful.

Attached is the gcode and a pic of one of the cuts. They generally al look like that. Some with bigger steps.

[ger21]

Tried changing the pulse and steps up to 4(maybe try 5?)

Try 15 or 20.

[Realmseeker]

It worked! Thanks Gerry. The screen in motor tuning makes it look like you can't put it above 5. Not to sure exactly what those settings do, but 15 did the trick. I can't duplicate it on large cuts as I am going out now, but it seemed to fix the problem.

Two days of pulling hair out, solved in an hour.....

[ger21]

It's a common issue with the G540. I think it's caused by poor quality signals from the PC, but not exactly sure.

[jsheerin]

That was my problem with the G540 - my PC's parallel port card could not source enough current to drive the opto-isolators in the G540. Thread about it here:
http://www.cnczone.com/forums/showthread.php?t=75784
I figured out my problem starting around post 15.

[Realmseeker]

Well the original poster on the thread had many of the same problems and questions I did. I am hoping that the fix Gerry just gave me holds out and I don't have to buy a smoothstepper or another lpt card. Frankly I am at the point where I am don't investing large amounts of money into the machine and have basically tapped myself out of money I could spend.

So this better work or else I am selling this and buying a carvewright! JK

[jsheerin]

If that is your problem, a parallel port card is about $10 plus shipping.

[ger21]

If it doesn't limit your speed, you can increase the pulse width up to 30-40, if you need to.

[jsheerin]

If the problem is insufficient current in the lpt port, I still don't see how increasing the pulse width helps this. I mean I know it does - it did on my machine at least some of the time. But looking at the input voltages to the G540 on a scope, increasing the pulse width did not make the voltage of the step pulses rise to a level that would make me think the G540 could see the pulses.