MPCNC Primo Tubes rotating

I’m having issues with my gantry pipes rotating in the trucks.

For most this probably isn’t a big deal, but if mine rotate too far, then my core is loose on the rails. (pipes are only round-ish).

I’ve screwed the locks in about as tight as I dare to go for plastic. Anyone have any ideas for what else I could do to keep them from rotating? I’m thinking about adding some electrical tape to the tubes where the locks clamp down on them.

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Maybe a screw through them at the truck?

Can you post a couple pictures? Have you measured the OD of your pipes? Are the pipes clean? Are you able to rotate the pipes by hand? Are there any anomalies on the printed parts that might be preventing full engagement of the pipes by the trucks?

If nothing major is amiss I think adding a little bit of shim/gasket/etc. sounds the pipe is worth a try. I would avoid electrical tape because the adhesive is no fun to remove.

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Seems to me the gantry rails shouldnt be getting that much torque. The core might twist them slightly unless the bearings are perfectly parallel to the axis, but even then the bearings should slip before the truck locks, unless the core bearings are super super tight.

If you loosen both truck locks can you twist the gantry rail?

I can twist the gantry rails by hand even with the locks tightened down.

Another thought I had was to sand the end of the rails with some sandpaper to scuff them up.

Are they super polished? I had some pretty shiny stainless in mine (which I had to relocate) but it still took some decent force to twist it.
Your truck clamps haven’t bottomed out, right? You just stopped tightening to avoid breaking them?

A thin layer of hot glue?

Is the gap on the lock closing up so you can’t tighten any more? If the gap is not closing I have a hard time imaging it still being loose…

I’ll take another look at lunch. I’m pretty sure there’s a little gap on some of them. Just afraid of cracking parts. Might just need to keep tightening.

I don’t have any more of the blue material, so if they break, then I loose my pretty colors :slight_smile:

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Not so bad if the screw cracks the clamp, but if the nut cracks the truck…no fun to be had.

It looks like the clamps are bottomed out on the trucks.

I did put furniture wax on the pipes to keep them from rusting. I’m wondering if that’s causing some of it. I’m going to try the electrical tape route and wrap a layer around the tubes just where the clamp goes.

That’s no good. I have kind of a lot of room left. What do you think is going on? Tube OD? Clamp is in the slot correctly? Something else??

This is how much room I have

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My luck in life?

This may go back to the Core’s clamps not getting tight on the rails either in my build. I do know my tubes are slightly out of round just enough to cause issues there.

If it were ovalling, wouldn’t they lock up at some point?

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I’m not having that issue. Where the oval is at the maximum is where the core is the tightest and where I want it to be. When it rotates away from that is where the core can wiggle.

I’m guessing since it’s rotating from tight to loose then the clamps on the trucks are slightly loosening even more as it rotates.

It could just be that the crap blue filament isn’t dimensionally accurate even though all my measurements test out correct. It could also be that whatever makes the blue filament slightly glossy is also making it slippery.

Who knows…

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Tape would probably work but you might want to do all 4 trucks to keep things in Z-ness, or if the clamps are bottoming out, i’d think you could add a thin shim to top of the truck clamp to gain a little more clamp-age.


I have no idea how this could even happen. My rails even have wax on them and are not going anywhere.

If they shipped 25 mm instead of what was ordered?

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They’re the right size. I measured them in another thread. When I say they’re ‘out of round’ I’m referring to a .2mm difference in one axis vs the other. Shouldn’t be enough to cause major issues, but apparently my build is special.