HELP Can't make square cuts


I finally have my MPCNC assembled and working, but I can’t seem to get square cuts out of it. I printed everything myself (no scaling) in PETG, and had no fitment issues while assembling. I bought the bundle from the vicious webshop. I have no endstops, and the total rail length is 31"x31".

I spent a few days last week trying to square up the frame unsuccessfully, but I printed the updated corners, and I’m now confident my frame is square (I used dowels cut to length to ensure the rails were the same distance apart, and the diagonals are within 1/32"). My squares are still coming out parallelograms, and circles aren’t perfectly round. See attached photos. Both sides of the square are the same distance apart and parallel, but the diagonals are about .5mm off on this ~20mm square. You can also see with a ruler that the corners aren’t 90 deg.

I pulled the 4 3" bolts from the center assembly, and then reassembled while it was all on the rails, but that didn’t seem to help. I’m not sure what to try next, and am starting to get frustrated…any suggestions?


So what usually happens is when you drag the tool around the rails get tweaked one way or another usually worse when you start in a corner. I am sorry I need to do a little guide for this but the answer is usually pretty easy. To try and describe what is happening if you have the tool all the way on the left side and pull it towards you, the right side will follow behind and give you crooked cuts.

Get the tool where you want to start then measure all 4 rollers and set each side equal (x and x, y and y). I measure from the corner block to the roller and check and set each side, and I usually double check.

Let me know if that isn’t clear enough.

Thanks! That makes sense and seems simple enough, I’ll give it a try.


Okay, so I had some time to look at this over the weekend. The rollers are definitely not square to the corners, there is almost a 1/4" difference between each side (roller to corner). I don’t see how I can adjust this though. I try manually moving each side; with the steppers both engaged and disengaged, but it just moves back into the original position as soon as I let go. Am I missing something?

Try loosening up your 4 long bolts in the center assembly. Sometimes they got tightened down so much you need to take them all the way out and put them back in being careful not to over tighten them.

Thanks! I actually already pulled these guys out at one point, but maybe I’m over tightening them (wouldn’t be the first time).

Nope, no luck. I removed all 4 long bolts and re-installed them, being careful not to over-tighten them. The gantry is still off square by pretty much the same dimensions it was before. Ugh. Where else can I adjust it?

Maybe tighter? Is your frame square?

Tightened everything down a little more. Still off, although it seems closer than it was. I tried cutting a 4cm square, and as you can see in the photo it’s still a little off.

I spent a ton of time getting the frame square. Diagonals are within 1/32" of each other and so are the side rails.

Are you setting the rollers before you start the cut, like I described in the second post? It should easily be squared that way if your rollers are only off by 1/4" when relaxed.

Are you cutting really fast and over torquing the frame? Are your tubes bent?

I’m not really sure whats going on if you can’t set them by hand before the cut, usually it can be pretty far off and still work that way.

Yeah, I’m trying to set them by hand before the cut, but it always goes back to how it is now. Maybe I’m not understanding the process of settings the rollers correctly.

I’m cutting with your recommended settings, feedrate is 15mm/s and only a .1mm cut depth in super soft wood. Hmmm…I’ll check for bent conduit, that’s possible I suppose.

I have been stuck thinking about your problem, what is the exact outside diameter of your rails, are they pretty round or are they oval? Also the middle end and joiner tension bolts can have an effect on squareness.

Copied from the other thread.

Not to many people seem to have this problems but when I try and replicate it it is because something isn’t “balanced” I guess is a good way to word it. I would say loosen up all the tension bolts including the 4 long ones and as you start to snug things up check the rails with a carpenters square, if don’t have one they are about $5 at the hardware store. This is how I have been checking on the new middle assemblies I have been making. If they aren’t square when it is completely loose something else is wrong, either with the rails being bent or your roller f’s are tweaked. The roller f are very strong and should hold it very square by themselves.

Thanks for the quick help! I’ll try these suggestions tonight and let you know what I find.


Ugh…I suspect all these problems are mostly or entirely user error!

I went through a bunch of the these suggestions, short of completely dissembling the middle section, and was still coming out with the same measurements (about a 1/4" off with the steppers relaxed.) However, just as I was getting frustrated, I figured I’d see if I could manually park the tool as you originally suggested. I plugged everything in, powered it up, and low and behold, when I manually moved the tool it would stay where I set it! Aha! Then, just as I was getting it close to square, the steppers stopped holding again. I think the whole problem is the steppers disengaging while I’m trying to set the gantry square for the cuts.

Here’s what I’m doing.

  1. I plug in my laptop to the board, connect Repetier Host.
  2. I move the tool with the manual controls in RH. Everything is working.
  3. I try to set the tool square to the corners. The steppers are engaged for a minute or two, then disengage. Is that normal behavior? I feel like I’m probably missing something really simple here.

a) Maybe your stepper drivers get to hot after some time and power off?

b) There is a setting in your marlin firmware:

// Disables axis when it's not being used.
// WARNING: When motors turn off there is a chance of losing position accuracy!
#define DISABLE_X false
#define DISABLE_Y false
#define DISABLE_Z false

I don’t know the exact behaviour of the disableing process, because I never set this value to true. Could it be possible that you set this value to true and after some idle time the steppers turn off?

You may have seen my other thread stating the exact same problem (I didn’t see yours before I resurrected mine otherwise I would have just posted here).

Viscous made mention about the outer diameter of my conduit, since I am using the international version (Australia) which is designed for 25mm conduit but the conduit I got was actually 25.4mm. Doesn’t sound like a lot but it means everything is a tight fit and things get bent out of shape. In addition my conduit is aluminium which is not strong enough and is soft enough for it to be bent out of shape quite easily with the forces involved.

So I am currently printing out the new corner pieces, and tomorrow will be getting 25mm OD galvanised steel conduit to replace all the aluminium rubbish.

I am pretty confident this is going to solve a lot of the issues I have been having so once I have it done I shall comment here with the results.

Hey Shane,

I saw your thread; it does sound like we’re having the same symptoms.

I’m using the 23.5mm edition, and my tubes measure around 23.4-23.45 and seem pretty round, so unfortunately I don’t think that’s my issue. That’s not to say one or more of my tubes didn’t get bent for other reasons.

The new corners do wonders in getting the frame squared up! I did the same thing when I first starting troubleshooting this, and they are so much easier.

I’ll be looking forward to the outcome of your part replacements.

My conduit is 23.4-23.45 and is round. I can’t see any bends putting a straight edge against it, but I can’t be sure it’s not slightly bent somewhere.

I loosened the middle joiner bolts a little, but not all the way as I don’t think I can get those bolts out without disassembling the whole middle. I have my machine in an enclosure, and removing the gantry is going to require taking the whole machine out (and unscrewing and re-squaring the frame) so I’m trying to leave that until the last option.

I’m hoping getting the steppers to stay engaged so I can set the start position resolves most of my issues. Is it normal for the gantry to be a little out of square when relaxed, or is still a symptom of something else wrong?