Rails not perpendicular

Hi there,


i’ve set up my MPCNC and everything works just fine. But the X and Y rails where the gantry sits on are way out of perpendicular and tightening the bolts does not bring any effect. I build it as the dual endstop version (just wayting for the endstops) but I would like to have it well configured anyway. The angle is about 3-5° too wide and i don’t know how to fix it.

One other problem is the height of the outer rails. I started with measuring the height of the upper rails (X in my config) and adjusted the feet so that the rails where on same level in all 4 corners. I then checked the lower rails and realized that they are not on same level. They differ about 1mm. The only answer is that the distance plates between the rails are not the same hieght. So i have to open all corners again to put something between the rails. Do you know this issue?

Any advice about getting the rails perpendicular?


Pictures, pictures, pictures! We need to see how you put it together to know what you have backwards. :slight_smile:

Give us images that show closeups of each assembly and pictures that show the whole build as well.

Particularly - is your build square? If your main rails are a parallelogram that’s going to really magnify where the gantry assembly rails cross. Mine was ever so slightly this way and I didn’t even know. It wasn’t until I tried running the cutter all around the perimeter to mark my max tool reaches that I found out.



I could not put pictures in because the mill is not in my home. I have some now.

Yes, the outer rails are square.

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I suggest using it as is for a while, to break it in. After a that the 1.75" and the 2.5" bolts might need an extra quarter turn.

Let us know how that CF holds up.

I will try that.

And I will do that too!


I have the exact same problem with my MPCNC…

The angles of the frame are all 90° and the angle where Sami was measuring is also a little bit higher.

I watched that the XYZ Burly bends a lot when I put the rods for the z-axis in and this causes the wrong angle, but I dont have any idea how to fix that…

I reprinted the xyz burlys and check the dimentions but they are correct.



Are you tightening the bolts too much? That will pull it out of line…

Thanks for the help but iam pretty sure that i tightened the bolts not to much.

I assambled and disassambled the whole thing 3 times and it wont fit…

A friend of mine has the exact same problem but he decited to let the stepper motors hold it in angle when he turns on the mpcnc



I am having the same issue. I think that I have a bolt on the xy that is contacting a bearing that may be causing the skew. Rotating the bolt helped but I think it is still causing the issue. Can you guys check your machines to see if you have more clearance? I will probably disassemble and grind that bolt head a little.


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Whoa…I wonder how many people are having this issue. Grade 8 must be thicker.

It was not my intention to use grade 8 but they were “prime next day” along with a bunch of the other parts ordered and I am impatient!

I beveled the head to allow more clearance although it didn’t help my alignment. I am gonna work the machine a bit and see if that helps.

Also my printer is running making the snap on alignment tools which will help show how far they are off. Using a framing square on EMT tubes that are on different planes is annoying :slight_smile:

I did print the crown on my garage floor in sharpie!

Thank you for the extensive engineering and design that went into this. It is truly a work of art.


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My problem is still there and i don’t know how to fix this…

It’s not the same issue like Aarons.

The picture shows that there is enough space between the bearing and the bolt, maybe i should check my printer if its perfectly alignet. (it should be)