Problem with New middle Assembly (bearing contact and squareness)


This is my first MPCNC. Everything was going fine until I got to the middle assembly. The 5 in bolt that runs though the middle of it was an incredibly tight fit. I had to use some C clambs to make a press to press it though all the parts. Then when it came time to insert my conduit the bearings on the front side (tool mount side) of the x and y blocks made contact just fine but not the back bearings (the side where you check for square). The only way I can get the back bearings to make contact is by really cranking down on that 5 inch bolt. When I do that I always end up at 91 or 92 degrees (out of square) and then the all thread going down though the Z feels really tight. It’s hard to turn by hand with the pineapple adapter. I fooled with it for about 3 hours and can’t figure it out. Any one have a solution? My parts were bought here.


Put up some pics so we can look for any obvious errors in assembly.

You bought the plastic from here or just the hardware?

I bought the entire bundle here. Printed parts, Hardware and Electronics. Is that 5 inch bolt supposed to be so tight? It really surprised me compared to the perfect fit all the other parts had. It was tight over the threads themselves and then it gets bigger over the smooth shaft. Thats why I had to use the clamps to act like a press. Until I tighten that 5 inch bolt really tight there is lots of slop between the conduit and bearings in the back. Pictures coming up in the next 30 mins. Also the all thread came with 2 nuts and a spring but I couldn’t find instructions for what to do with them.


The extra parts go with the old parts. You don’t need them. The bolts should be tight but it also shouldn’t be an issue. Did you get the 23.5mm parts or the 25mm? What size conduit do you have, there should be no slop before that bolt goes in. It is actually a slight (.2mm ish) interference fit.

Did you put it together in the order of operations in the instructions?

The order history says 23.5 , the emt I bought from the local hardware store it just says 3/4 inch ID EMT. I don’t have calipers to measure the parts I recieved or the conduit. I could get a pair though. I’m having trouble uploading pictures from my house because of slow Internet.

Finally got the pictures and the short video to upload.

That leadscrew should not be out of place like that, It could just be the nut holder under it is out of alignment.

Not sure what it could be. Are the 1.5" bolts loose, they should be? If those are too tight you could be throwing it all out of wack. If the conduit fit in the front half there is no way the back half shouldn’t fit. You didn’t put the bearing spacers in there did you just bearings right? Tighten the 5" bolt and it should take up the slack.

I know the parts are good I just built 2 more machines and they fit great. I checked all the pieces on 4 more sets I have printed and the only part that has some friction to the 5" bolt is the XYZ plate all the rest slid through by hand.

I went over to take better photos but couldn’t really get what I wanted. Right now i have all torsion screws loose and I’m only get contact on 2 out of 3 bearing both front and back and left and right xy mount. Now if i tighten torsion A bolts the front 3 bearings come in contact nice and smoothe, but those back sets won’t unless I really crank down on torsion B (5 inch bolt). My z is perfectly fine and so are my motor mount assemblies.

Spin your conduit it might be an oval. If that doesn’t help tightening the 5" should be fine.

None of the torsion bolts are tight, no bearing spacers. The back bearings will make contact if I really tighten that 5 inch bolt but that jams the lead screw and locks me at 92 degrees so I’m out of square.

None of my center assembly slipped over that 5 inch bolt. They all had to be pressed on. Spacers and all.

I took it completly apart, ill upload videos soon. I had to beat things apart with a hammer.

You can very easily break things with a hammer, please be careful. If you have it apart it would be easy to just drill out the 5" bolt holes with a 5/16 bit.

You would be suprised how hard I had to to hit that 5 inch bolt to get it through the center assembly, speaking of which. Ill be ordering a new bolt if I can’t find one at the hard ware store. It’s a little bent.

I usually just put pressure on it while turning and it kinda just un-threads out even when there is no threads.

Idk. Those top and bottom gray brackets wouldn’t go from the threaded part to smoothe part at all, and the rest of the parts wouldn’t hand fit. Maybe it came a little bent. I tried for a while before I used the c clamp. I just hope a new bolt fixes it. I’ll look tomorrow at the hardware store or I’ll order it from you, no big deal.

Thumb detector never fails

I bought a new, almost identical 5 inch bolt this morning. I was able to get the assembly square, but in order to get all bearings touching in the back I had to really tighten that 5on bolt. Enough so that it warps the entire center assembly and it jams the lead screw. I will try another section of conduit from another store but I haven’t had any problems with the reast of the build.

When I have that 5 inch bolt loose, in the back only 2 bearings are making contact with the conduit and the third has a 1mm or so gap.

Edit: added 2 more pictures showing the gap

It does not make sense. the large xy pieces are an interference fit and should flex open to fit the conduit without a bolt in it, and the 5" bolt should do nothing to change the conduit angle. I have to assume your conduit is the wrong size.

Of the pieces that didn’t fit smoothly here it was from print blobs on the inner surface. I chased the holes with a 516 drill bit and everything is smooth now. I will do this before I ship any more parts from now on.

I didn’t get a chance to get new conduit today, but get a hold of me. I would like to know what the price would be to buy a new center assembly, printed parts only.

I’m wondering if when I had that bent bolt in if I exerted to much force trying to get it square and tweaked the xy brackets.


I don’t think you can really tweak them without cracks forming. I would just drill out the holes that the 5" bolt passes through and give it a try. Verify that your conduit is the correct size as well. If anything it should be a tight fit, never heard of a loose fit. What letter is printed on the parts?