Starting my first MPCNC build and a question on squaring the frame / roller assy


I’ve started building a MPCNC machine, great design by the way. I’m printing with a well tuned PrintrBot Simple Metal and getting very good prints. Dimensions are very good and repeatable, and so far I haven’t had to drill any holes. The 5/16" holes are nearly perfect, no appreciable slop, etc.

The initial MPCNC is a 24" x 24" frame size. Starting small until I can verify that everything works. Then maybe will build a slightly larger machine, but this size should be fine for my immediate needs. I already have some steppers and UNO with GRBL controller from an earlier project that I’m going to start with.

I have the corner pieces printed and one set of roller assembly parts. Plus some of the smaller parts, and working on the second set of roller pieces. Then will be printing the feet and finally the center and Z axis parts.

But I have enough to start looking at squaring up the frame and that is where my question comes in.

Following the assembly instructions it looks like I have the frame squared up. That is measurements match at each end of the outside rails as described in the instructions.

But when I roll the cross bar from end to end there is a small gap on the end when moved to the corner blocks. For example with the roller assy with conduit pulled all the way towards me the right roller assy is touching the corner block but the left roller assy is between 1/8 to 1/4" away from the corner block. And if I push the cross bar all the way to the opposite corner pieces then the left roller assy touches the left corner block and the right roller assy has the 1/8 to 1/4" gap.

I am wondering if there is something with the roller assy’s as I printed them that is impacting this since measuring the distance between the corner blocks seems to indicate that things are square as far as the outer frame is concerned, but seeing that gap and having it switch to opposite corners makes me think that I’m either not measuring the correct spot for squaring the frame or that I’m missing something and I’m not really squared.

Has anyone else run into something similar?

I just placed an order for some odds and ends parts from the store. Once I get the CNC machine working I’m thinking about ordering the extruder so I can turn this into a larger format 3D printer when I need it.

I went back and triple checked and I had the corner blocks oriented differently than in the frame assy pictures. I changed the blocks around and made some measuring dowels so I could check the distances between the conduit and not just the corner blocks.

I’ve got it almost 100% now. At one full end of movement the cross conduit and rollers perfectly butt up against the corner blocks and the other end of travel is very close, so I think just some more fine tuning now that I have my dowel gauges made and cross checking corner to corner and I should be at 100% square.

Glad to see you got it figured out. Squaring it up good just takes time and patients. I built a 24x24 and it’s the perfect size for my use. I printed mine with a printerbot simple, the wood version. It has a slightly smaller print bed so I had to get creative on a few parts.

Good luck and post some pictures when you get time.


Thanks Dave,

Things are coming along pretty well, just taking time to get all the pieces printed. Once I made a “jig” to make measurements more accurate the frame is squaring up quite well. Final adjustments will have to wait until I have all the feet printed.

It took me a while to get the PrinterBot Simple Metal really dialed in, but now it produces amazing prints. Nearly perfect every time. That is no blobs or unexpected holes with very good adhesion with PLA. I have the parts to add a heated bed but since I’ve been able to get good results with PLA and Blue Tape I haven’t bothered setting up the heated bed, but I’m going to be doing some ABS in the future so I’ll really need to add that to the PrintrBot.

I’m sure that I’ll have more questions on the MPCNC as I get closer to the finished product. I expect to do a motion test of the X/Y in a couple of days at the rate things are going.

And I’ll post some photos once I get the feet done and have things mounted on the base.