Scaling problem with MACH3

We are in the process of building a small CNC 3 axis milling machine that relies on MACH 3 to control it. Both the X and Z axis work perfectly but the Y axis does not. The scale is not correct but what is worse is that it depends upon which direction it is moving. For example If I tell Mach3 to move the Y axis 40 mm it moves 45 mm and if I tell it to move - 40 mm it moves 35 mm.

I can confirm that there is no problem with the stepper motor as I have replaced the old one with a NEMA 17 from a Rotalink one with the same problem. I have tried both a Stepstick driver and an Easydriver with precisely the same results. Perhaps I have accidentally adjusted some settings on the MACH3 program without realizing.

I would be grateful for any help regarding this problem.

Double check your "steps per" in Config>motor tuning.
At what microsteps are you running on the drivers?

Hello Sockles,
The steps per is set to 1600. My lead screw pitch is 1 mm and my y stepper motor rotates in 1.8 degree segments with added resolution of 8 times micro-stepping. However whatever my steps per is it does not account for the difference in distance travelled depending upon the direction.

Are you in absolute mode?

If your at Y = -5

and do a G0 Y40, it will move 45mm.

If your at Y = -5

and do a G0 Y-40, it will move 35mm.

If you do a G91 for incremental mode, then the above code will move 40mm each way.

I shall try this but it is not always 5 mm out because if it were told to move 20 mm it would probably be 2.5 mm out but I may be wrong. Thank you for your feedback Ger21.

Quote:

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Originally Posted by Shed123

I shall try this but it is not always 5 mm out because if it were told to move 20 mm it would probably be 2.5 mm out but I may be wrong.

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Then set the steps per for that axes, they are not set correct

Open Settings Tab, Then Just above the Reset Button, you can do your axes calibration from there, just follow the instructions, & you will get it as perfect as you want it, depending on the method you use

Unfortunately this did not solve the problem. I did notice that in the general config window I had the "Perform G92.1" box ticked. I have had a general look around on the internet for anybody who had a similar problem to this one but have found no-one.

I may not be making this quite clear. The distance that the Y axis moves is dependent upon it's direction. I could not work out a way to make the Steps per to be correct in both directions.