Error difference

Hello, just cut a piece of acrylic 420x86mm, some holes on it nearby the edges and realize the left side is 1.5mm shorter than the right side, this starts to increase after about 110mm so at the end of the piece instead of 86mm I got 84.5mm.
Can I make this difference smaller?

Have you verified that your machine is ‘square’? Easiest test is to draw the largest rectangle you can with your machine (probably just using a mounted pen), then measure the diagonals. If the measurements you get are the same - the machine is ‘square’ (at least in X and Y), if not then it’s out-of-square.
If out-of-square you’ll need to do some tweaking to try to get it (and keep it) square.

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Last time I checked it was, I will try again back home, the tweaking would be?

Either installing manual stops to hold the gantry square while you power-up, or installing dual-endstops and using the auto-squaring capability built into the dual-endstop firmware.

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I have dual end stops in mine…

Did you do (or redo) the calibration steps at the bottom of this page in the docs:

Test and Calibration? well did only when finished the machine, almost 3 months ago. Should I do it again then?

Since it looks like your machine isn’t cutting square, I would at least do the tests again and see how square it is. From your original description of the problem, it looks like it’s cutting out of square, but perhaps that’s not the real problem? I would do the squareness tests first (drawing large rectangles, measure diagonals) to at least see where your machine is at right now. Who knows, maybe your endstops got jostled and moved? i don’t think it would take much to be off 1.5mm in 420mm.

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If your table is wood, it may have moved due to weather/seasonal changes.

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I don’t see how that is caused by being out of square. The motors should travel the same 86mm on either side. The diagonals would be different if it wasn’t square, but not the length.

Can you try the same cut in foam? Home depot sells that purple HD foam that cuts very easily. If you use the same gcode, and get them to be the same size, then it is working too hard in the wood, or something is flexing.

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Did you cut out the entire thing, as in all four sides? If you did, and have two different lengths you skipped a step (usually visible step somewhere, usually speeds or rapids are wrong) or a pulley is loose.

If you only cut three sides, your machine or the mounting of your work piece could be out of square.


It is table but I am not sure, I live in an apartment, my MPCNC is in one of the Bathroom lol. A[quote=“barry99705, post:9, topic:15145, full:true”]
If your table is wood, it may have moved due to weather/seasonal changes.

The table is wood, my MPCNC is in one of the bathrooms and there is no way to get weather, too hot here so air conditioning 24/7.

I will try to find some foam here in the desert, I thought plastic should not be too strong. 2mm.

Yes, it cut all four sides I fix with two faces tapes a 2mm acrylic, how can the X side is perfect and the Y side has this difference. I will check the pulleys again.

I don’t have a pen mount, but instead I make 4 holes of 2mm in each almost end corner and the measures came as 57.2 x 57.8. I did not understand what should I do now, measure XY diagonal blocks and move the X to the right 6mm? And thereafter change the size of the bed to?

Moving both X points won’t help. That will just make it shorter. You need to move only the lower left along the X. 6mm is too far, it is closer to 3mm.

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@jeffeb3 Do you mean move only one of the X blocks (lower one) to 3mm to the right? In my understanding if I move this lower X block to the right (means shorter), when I Home X it will stop before the other X block, right now the blocks are in an identical position and trigger together the homing. Am I too wrong?

This is exactly why we have dual endstops. If you move the botton left endstop 3mm to the right, then the top motor (on X) will keep moving when you home, which will slightly adjust the angle. After that, the gantry will be “more square” and your diagonals will be closer to the same value.

If you don’t have dual endstops, then this won’t work.


@jeffeb3 I Just reduced 4mm the measures are perfect 57.8x57.8.
but now when I home X the lower part touch e the block earlier than the other making the machine like twist a little. I made a video better than I try to explain but I could not upload, if you want is in this link.

That’s because it isn’t square when it is relaxed. You could alternatively move the Y block in tye lower left up a few mms.

But really, this is doing exactly what it is supposed to do.