Endless squaring battle

I built MPCNC almost 2 years ago, and I am continuously battling trying to make it relatively square. Sometimes I think I win small battles, but looks like I am losing the complete war.

I havent been using MPCNC for a month or so, and I went to use it today. Previously I precisely squared it, so I was expecting perfect cuts. After cutting the first test, I found that it completely lost its squareness, once again.

I began squaring it again, but after some hour or so, I stopped because this time the situation is more sad than previously. This time I am unable to tighten the rail block at all. Some of bearings are not having grip at all.

The upper bolt is tightened as hell, but the rightmost bearing is not touching the rail…[attachment file=51433]
What will you recommend as the quick solution, and what will be the general one? I’ve got feeling that PLA is not stable in the time perspective, and possibly losing its form under load? Also, it might be the change in humidity that affected the form (it is cold winter here, and humidity is extremely low)

What material do you recommend if I decide to reprint these rail blocks?


If you are not using the dual endstop firmware you 100% should be checking for square on every cut as we have for the last 2.5 years. Move your carriage to the starting position and measure the rollers to the corners and move it into square, by making both measurement on the same axis equal. It takes 30 seconds. Dragging around the gantry is never intended to hold perfect square no matter what. Once the steppers are engaged they will hold any position they are in.

Does that make sense? Make sure your corners are as square as you can get them and set the gantry before every cut.

As for the bearings, you might actually be over tightening them if they are coming off the rail.

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An easy fix to get all those bearings to contact is to take the motor mounts apart, use a heat gun, slightly heat the plastic and push it inwards, to get a tighter fit.

That’s how I did it, worked great.

Once this is done, you can use the dual endstop technique to get repetitive and accurate square cuts, since otherwise you’ll be out of square any time you stopped your machine or moved it by hand

PLA remains the best material for those parts anyway, since it is one of the stiffest.

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If you have to melt the parts something is wrong they are all an interference fit by kind of a lot.

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