Cant get the trucks square

Hi, im building the mpcnc for the first time and i just dont know how to make the trucks go square. Im getting 8mm off in the X axis an about 7mm on the Y axis. I spent a couple days trying to square them by the tension screws and got no lucky.

I even rebuilt all the feet and got the diagonals dead right, (not a single milimeter off, realy) but that didnt solve it.

Any thoughts in how to solve it? I guess i will put the core on and try to square with it, or i realy shouldnt?

Thanks in advance and sorry for the bad english, im from brazil and skip some classes lol

How are you moving the gantry rails? If you’re moving only one side the other will always lag behind. If you move it by pulling on the center of the rail, can you easily move both trucks to the end of their travel?

It doesn’t look like you have hooked the belts up or powered the steppers. I would ignore the squaring for the moment. If you can get the trucks to the end of travel (at the same time, manually) then you should be able to get them tracking together when they are powered on.

One thing to remember: put the trucks both against the stop, when you turn the machine on (or tell it to mark the origin) then see if when you move the axis that both trucks move the same distance.

In that case, the steppers keep it “square”.


Hey Mike, thank you for your reply. I’m moving it by pulling the center, i’ve tried doing by the outter edges but got the same results. I can easily move both trucks almost to the end but in the last part (those 8mm) i gotta force it to touch the end.

I didnt hook up the belts nor turned on the steppers yet. Im also will not have the limit switches wired because my board wont support them. The board i will use is the CNC Shield for the arduino uno, and it has room to just 4 steppers and 3 end stops (x, y and z).

Guess i will proceed with the core and eletronics and see if the steppers can hold it square.


At this point of construction my primary concern would be that movement is smooth and easy. The other compliments still to be added ( core and belts) will establish and maintain squaring.

If you search for this exact topic in the forums I’m guessing similar posts will come up. I know because I asked the exact same question during my build. The answer I was given from others on here which turned out to be correct is that it doesn’t really matter if they are square.

The machine has some natural slop in it which gets taken out when you get everything together and energize the motors. Once its all buttoned up you can square it up (literally just move it to square with your hands) then send power to the motors and it should stay square. Another thing Ive found is that it doesn’t really matter that much even if its not square for a lot of tasks. Lets say you have a square work piece. When you put it in the machine you can zero the machine to the 0,0 then just move the gantry in the X+ direction only until you get to the (L, 0) position of your work piece then just move the work piece to where its lined up with your bit. Basically you can square your workpiece with the motion of your machine not not necessarily with the table itself. There are many ways to make it work.

Alright, today i will assembly the core the way it is. Will come back later with the results. Thank you all, really appreciate the support.

I yielded much better results from squaring after installing the core. I took the motors off and jumped back and forth between the core and truck squaring methods until I got it square.

I think once the steppers power up it should hold the position reasonably well