Alright at the beginning on this year I build a cnc machine using the gecko g540 and mach3. I got it running and it has been running just about every day with no problems! I just recently build another machine exactly like the first one but with this on I am having a heck of a time. I have it all set up and started to run my first program on it and it started to fade of to the right of the work piece about 1/4 of an inch. I stopped the program and zeroed my machine and when it went back to zero it was off about 1/4 of an inch from where it should have zeroed. So I have check and made sure that my rails are good and not binding or anything then ran it again and the same thing happened well then I check my bearings and my pulleys and made sure the belt was good and not off. After this I ran it again and it still did the same thing! So I thought it might be my stepper motor so I had a new one laying around and replaced it with that one and ran the program again. It didn't make a difference it did the same thing it was off about 1/4 of and inch when I went to zero it. I have checked the motor tuning on mach3 it should all be the same as my other machine because I just copied the xml from that machine to the new one. I am just out of ideas! I have no idea what it is doing and why it is doing it. Could it be mach3? has anyone else had this problem?

What is the current setting when the stepper motor is in idle?

Presume it's the z axis...
Consider you zero the machine, then tell it it go to the cut location (xy), turn spindle on, lower to cut height.... and move the x and Y... problem is, the z axis has gone into idle current setting... my drives are infinitely adjustable for the idle current... not a problem for plasma (no cutting forces)... little problem for milling...

Is there any way you can monitor the z axis leadscrew whilst cutting? (Bit of electrical tape... tippex mark on stepper motor shaft?)

Gecko g540... what is the resistor across pins 1-5... and what is your rated motor currents?

It is the x axis and the y axis that are off they both will be off but the z axis is just fine. My motors at 2.8 current rating and I have 2.2k Ohm Resistors, 1/4 W, 5% resitors going from pin 1 to pin 5. I know that I should have 2.8k ohm resistors but on my old machine I had these resistors and my motors would get really hot so I switched them out for 2.2k and it works great.

I guess I could try and change the resistors on the new machine to 2.8k ohm and see if that will help. But I don't see why it would make that big of a difference.

I thought it was the z, ignore above advice or suggestion.

Sounds like your machine is loosing steps (or something is loose).

What is your x and Y max velocity, acceleration, and steps per unit.

What feedrate, spindle speed, tool diameter, tool material, tool coating, number of flutes on the tool, depth of cut, material were you cutting when this is occurring?

I would suggest you check the tuning on the machine ... get an excel spreadsheet and type g00 x100 (if metric, say 2/3rds of your axis total travel), and the g00 x0... for 100 lines then copy and paste to a text file, save as a *.tap file and test your x axis.... do the same for the Y, then do a blended one (g00 x100 y100 /n g00 x0 y0)

And check how much your machine is out... now bear in mind that this is without any cutting forces si really you should determine where your axis begin to loose steps with acceleration and velocity then cut both numbers back by about 60% and it should be fine.