CNC size vs Design


Long time Lurker, first time poster.

I have built a MPCNC over last few months, and as many are, I am impressed with the design, really well done, and thank you for making it publically available!

I am still in the process of finetuning and figuring out the details, I intend to dissasemble the middle stack soon after I have done a few more runs, and rebuild it, hopefully it will then fit a little better.

One issue I am having is that the designs i have made end up being milled 30 - 40% larger than I intend. Is this a stepping setting issue? I have all three jumpers installed below the stepper drivers. I haven’t been able to find any comments about a size change issue.

I have used Aliexpress electronics, Ramp 1.4, DRV8825 and smart LCD. I am using ESTLCAM to convert Inkscape made SVG files, and printing via Pronterface.

Appreciate your feedback to see if I can get atleast similar sizes between design and end part.


Are you using 20 tooth pulleys instead of 16?

Thanks for the kind words!

I ordered 16 tooth pulleys, and then didn’t count them but i will check that I did receive the right ones.

Ă“k, so thats the issue. I ordered 16 teeth pulleys and received 20 teeth pulleys!

Is it an easy change to update the software to reflect 20 teeth instead of 16? Is it something i can do myself?

Yes just update the x and y steps in the firmware.

Is it only changing:
#define DEFAULT_AXIS_STEPS_PER_UNIT { 200, 200, 4535.44, 200 } //MPCNC


#define DEFAULT_AXIS_STEPS_PER_UNIT { 160, 160, 4535.44, 200 } //MPCNC

in the configuration.h?

1 Like

Yes, perfect.

Fantastic, this has solved my size problem! On to the next one!

Thanks for the support!

What, no next one…positive attitude. Get ready to get it dirty and have fun and maybe learn some things along the way.

I like to fight it first, see if I can figure it out… Have some positioning issues to work on, in terms of how well layers are on top of eachother, but i think that is refitting the centre assy, and making sure belts are tight etc. I will be back!