Core is becoming loose with use

Hey guys, I’ve noticed that after using my PRIMO now for a while (a couple of weeks) the central core has developed play in both directions. When I have the stepper motors locked I can grab the top of the core and feel/see it tilt on both axes. I’m assuming there are some bolts that I need to tighten but before I go crazy just tightening everything I’m hoping to do a quick pulse check to see if anyone knows from experience which set of bolts need to be tightened. If I go around I can feel several of the bearings are no longer making contact with the tubes but like I said I’m not sure what bolts to tighten. I tried to go back through the build instructions but either I missed the information or it wasn’t clear enough how to tighten everything.

Related question, is it normal to have to tighten things after running an aggressive job? Or is this an indication that maybe I’ve pushed the CNC beyone its limits?

These are the two bearings that I can see a gap between the bearing and the steel bar and spin by hand.

I stumbled across this thread that talks about taking the CNC apart after “breaking it in”. If I have time I’ll give that a shot today and see how it goes since I haven’t gotten any other suggestions.

I regularly inspect my Primo after use.

It is printed plastic. This is not the most stable material in the world, and it is normal for it to drift some, partilularly under stress. If you overtigtened the adjustments with your initial build, it will be worse, and have less accomodation later.

Even if you did not overtighten them, or moreso if you left them a little loose, then they can work their way loose and come out of contact.

There is a little bit of tightening on those bolts at the end of the bearing holders, but I think that’s more for squaring the gantry.

The bolts holding the bearings to the core might need a bit of tightening on order to close that gap. It is only the plastic ridges on the core and on the bearing holder that determine the distance that the center bearing is from the core. Any stretching of the plastic, or wear between the nut or bolt clamping faces will cause this to loosen a little, which would cause what you see there. This should be a quick adjustment.

These bolts featured here

I left everything quite loose, and had to tighten up a few things after several hours of use.

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Yeah, I was extra careful to follow the build instructions and ensured I never over tightened anything but now after several hours of use I’ve noticed there is play in the core. I’m assuming the play in the core will cause chatter since the whole thing can freely wobble left/right or forward/backward. I’ve tried tightening the bolts that hold the bearing and the gantry clamps to the core but I’ve been afraid to over tighten them and ruin the core so I have to reprint it. Are you suggesting I slowly tighten the pair of bolts that hold the gantry clamps to the core?

Well, I didn’t go crazy but I did tighten those 8 bolts up a bit. Probably only tightened them like a half-turn or at most 3/4 for one that was quite a bit looser. I’ll continue to monitor the core for play in the future. Thanks for sharing your experience and pointing me in the right direction. Greatly appreciate it.


I had to tighten mine a few times after the first few jobs. It’s been pretty consistent here lately. I also think the PLA is susceptible to heat/cold cycles sitting in a garage or shop.

Did you tighten the 8 bolts of the core clamps? Same issue here :confused:

Its really funny that you would respond today of all days :slight_smile: because I did tighten the 8 bolts the hold the core to the x and y bars and that seemed to help a little but I just took these videos to show that it is again loose… I’m starting to wonder if maybe there are other bolts that I should be tightening… I feel like the bolts are pretty tight now but if I really wanted to I could tighten them even more. I’m afraid to do that though as I don’t want to crack or deform the parts. How tight is too tight?

Yeah it looks like I have the same problem. I have been cautious so far because the machine is now square and I’m kinda scared it will be out of square. I’ll try the same bolts and see what the result is. It looks like it went okay for about 8 months with your MPCNC, or did it start to wobble earlier again?

I did do much cutting the past few months, I mostly ran a needle cutter which puts little to no stress on the frame. I don’t recall it being loose but when I did go to try cutting again this past week I made a mistake and the tool went way too deep and started skipping steps on the x axis (I feel like there is more play in that direction actually) so I’m wondering if maybe that is what caused the parts to become loose again? If anyone else is listening in on this topic I’m curious if I can just reprint the clamps that connect the core to the tubes and “start fresh” or is the core the part that has been damaged and needs to be reprinted?

I tightend those 8 bolts and it seems that it solved a lot of the problem. There is still some movement but I assume that is coming from the printed parts itself. The real play on the tubes seems gone.

Ryan said in another thread I have to check the 4 bolts that hold the bearing in the brackets as well. A reply from Dan provided some additional insight but I’ll let you read up on it yourself. What parts do I need to reprint?

Turned out those where the bolts I thightend. So far seems to work