MPCNC Primo is getting out of square and distance doesn't match

Mostly Printed CNC - MPCNC Troubleshooting
1

Hi,

I invested some days to figure out how to perfectly square my MPCNC.
Build size is 610x610x81mm and I managed to get perfectly matching diagonals and sides by drilling 5mm holes in each corner, putting precision dowels pin in and measuring distances and diagonals.

However the distance between those dowel pins is -0,77mm less than it should be (584.23 & 594.23 vs 585.23 & 595). I ignored that and adjusted the diagonals. Perfectly square!

Then I switched from a 3.175mm cutter to a 2mm and suddenly the machine isn’t square anymore. The distance between the dowel pins for X in the back don’t match the one in the front, Y both match. The diagonals are off by 0.5mm which doesn’t sound much but that would result in one side being 2.67mm shorter than the other side when routing 600x600 plates.

I tried adjusting steps to get perfect X and Y distances however as I did that after the switch to the 2mm cutter I don’t know if it worked or not because the diagonals were off.

I have dual endstops, Klipper and use F360. Motors are the Stepperonline 48mm 2A ones which I run @ 1.2A. tmc2209 and powge belts+ pulleys. Stainless steel rails, Makita rt0700 with a 1/8 collet from Elaire. Belt tension is equal for all 4 belts.

20220726_165910
20220726_1659104000×1800 1.4 MB

Any ideas why that happens? Also from reading through the forums it seems like diagonals off by 0.5mm is acceptable. That would, as said, cause one side to be off by 2.6mm which is worse than I could do by hand.

Edit: I used Loctite on the pulleys :stuck_out_tongue:

2

First, I’d make sure the Z axis is firm without any slop. Occasionally on this forum we see builds where the core clamps have been over tightened, and the clamp cracks. The result is a loose Z axis. Given your varying numbers, I suspect some issue with the Z axis, not with your diagonal setup.

Second, run your square test with pen and paper, not with the router. With pen and paper, you mitigate many factors that impact the measurement. Draw squares of known sizes. Measure to determine both the side sizes and diagonals.

I tried adjusting steps to get perfect X and Y distances

This method of making adjustments will not end well. I would start by calculating your steps based on your hardware and microstep configurations. Make your adjustments to square by adjusting your endstop positions, or possibly you can adjust the diagonals in Klipper. Marlin has a setting for this.

0.5mm is acceptable. That would, as said, cause one side to be off by 2.6mm

I calculate that a diagonal off by 0.5 would put a side off by potentially 0.375, but maybe I’m missing something.