New build MPCNC…works OK, but wrong measurement on peace

Mostly Printed CNC - MPCNC Troubleshooting
1

The MPCNC is working perfect except the size of the cut piece is less than the design.
Example: The design peace is 7.5’’ and the final is less than 7’’. The proportion of the piece is OK.

How can i adjust the stepper to move the exact number ?

Is there a tutorial on that ?

I’m using:
Hardware from V1
SKR pro 1.2 with V1 firmware

2

To specified, i’m using:
Repetier for sending gcode
Vectric Aspire for design (with the PP file from the forum)

3

This is a strange amount to be off. Usually people are off by more indicating a “wrong” pulley, or the microsteps set wrong, or less indicating a deflection issue. One scenario for the numbers you mention is cutting on the wrong side of your lines with a 1/4" bit.

I suggest:

  • Author the cut of a square and attach the g-code result to a post. Please specify the size you believe the square should be and the diameter of the bit you used in authoring. We can take a look and verify that the g-code would cut out a square of that size.
  • Assuming the g-code is correct, make a cut with that g-code and measure the result in both X and Y direction.
  • With your router raised and off, apply some force to your bit to see if you get movement/deflection.

Note there are easy ways to adjust the steps per mm if that somehow turns out to be the issue, but since you purchased your hardware from V1, your steps should be correct, so I’d do a lot of looking elsewhere before making a steps-per-mm change.

4

To understand where the problem lies, perhaps you should mount a pen and then draw a square x100 y 100 mm from the TFT and check what measurements you get. When you post your result someone in this forum can help you solve the problem.
Good luck

5

Thanks, i will try that and post the results……

6

If you’re using parts from the V1 store, the firmware should already be configured to the settings that match for step/mm.

In addition to checking cutting on the right side of the line, I’d look for sources of mechanical slop/backlash in the build. And I would start by making sure the set screws in the pulleys are tight on the machined flat of the motor shaft. Add a little temporary thread lock compound if they were tight at one point and are loose now.

7

OK, now i did a new simple square with Aspire and export the gcode.

And now the measurements are all exacts.

Maybe it was my initial design or something weird happened.

All is good now……Sorry All for nothing, it was probably and error on my side.

Thanks for your help, it’s very helpful….

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