Been building the J Primo (upgrade from C 525, build post due at some point), and went through to squaring only to find that the core clamps aren’t really making any adjustments when I change the tension bolt. Found advice from 25mm primo core clamp issues and tried to follow the steps:
Took all core clamps off and sanded bolt holes to allow bolts to easily slide through.
Fit tension bolt/nut/bearing on and tightened to snug (and tight to test it), then put each clamp on the core, starting with the top bolt and then the bottom. I had to stretch the clamp to get it to reach the opposing bolt (likely from the tension bolt being tightened).
Loosened tension bolt and tightened upper and lower bolts to snug.
Run the rail through.
The rail still only makes contact with two of three bearings. When it was mounted to the trucks/gantry, only the top two. When sitting on the table, the bottom two. I have been messing around with tensions in all three of the bolts but even if the contact is fine, then it rolls wobbly (and the rail can wobble as well). I saw David’s thread Texas Primo (Upgrading a part Burly/part 525) but as best as I can tell, my rails are round. Hit them with the calipers and got 25.4 +/- 0.2mm or so.
I’m likely not tensioning the clamps properly, but leaving them all loose definitely doesn’t help, nor does having them completely tight. Tightening the tension bolts didn’t seem to have an effect when squaring the gantry; and movement when attached to the trucks (and now I’m finding when just running a rail through the clamps) is choppy. One thing I noticed when trying to square the feet was that my table’s MDF surface isn’t completely square dimensioned, so I probably shouldn’t have used it as a reference. The length from outer foot to its opposite on the front and back x-axis is 36" (correct), and the diagonals were as equal as I could get them before I drilled and attached the feet. However, the left Y rail sticks out a couple sixteenths (sorry, no tape measure with mm) more than the right Y rail. Even if the right side is longer than the left (tubes were cut equally), if the diagonals were equal then shouldn’t it be square? Or should I take everything apart and resquare the legs?
I know it sucks to back up so far but if everything is out of wack maybe you are just beyond the amount that can be adjusted…you can check though. Make sure the Z axis is in the core, and the X and Y rails are in the core, but not on the trucks. If all the bearings do not touch there is another issue and lots of pictures are in order.
Thanks, I will take another look at the feet tomorrow and see if I can remount them better if necessary. The adjustability of the feet came in handy as I slowly screwed them down to keep them in what I thought was square.
Good news on the core (sort of), I loosed all three bolts on each clamp and ran the rail through each pair just to test it (and so it wouldn’t be too tight until tomorrow) and the movement was much smoother. Didn’t pay attention to all bearings making contact or not, but it felt better moving the rail. Then again, that leaves a lot of play.
Spent this morning getting the axes square - X and Y are same distances apart and the diagonals are equal. Definitely feel better about them.
The core is now the problem for sure. I’ve filed all the clamp bolt holes so that they can easily slide in and out. With the Z axis in and/or out, the rails are behaving the same. Sliding them through the clamps is pretty bumpy. Main bolts are just snug, tension bolts don’t have nuts on. The rails slide best when the core is turned such that the rail sits on the two core bearings.
Only filed the inside for the bolts to go through; spacer and opposite side should still be flush. I’m checking again and the rail (when core is standing up) only makes contact with the top and left bearings consistently, the bottom bearing occasionally. I can push and pull the rail and it will coast to the opposite end pretty smoothly, just without full bearing contact. Still kind of bumpy, as in it reaches a certain point and the tension bearing stops making contact then immediately picks back up. Feels like the tension bearing needs to push the rail toward the core bearings more so that they all make contact.
My rails roll flat on the ground.
Am I making this a bigger issue than it should be?
Edit: I’ve retightened the core bolts until they just make contact and begin to resist, so that the clamps can’t move (probably looser than I’ve tried before). Sometimes only one bearing is making contact; other times it can be two (any combination) or all three (least likely). Pulling the rail into the two core bearings feels good.
I can say for sure it isn’t the bearings - I cleaned all of them as someone else mentioned they ordered bearings that came and were greasy and slow moving. I didn’t realize at the time that that isn’t how they should be. It took that and all of one minute to realize that skateboard bearings should spin really easily. Overnight soak, rinsing/compressed air dry, Super Lube oil and they all roll much better now.
As for the tubes, is it because I’m using mild steel tube, not the specific DOM type? Is there a way to check roundness? Tightening the tension bolt is now getting all bearings to make contact a majority of the time, but now gets stuck at some point. Rotating helps a little. I’ll keep looking for a perfect point if it has one.
I ran the rails on the kitchen counter and saw a fair bit of light. Pressing down on it would seal the gap. Not very happy but I hope if I get actual DOM tubing that it will fix my problems with no reprinting. I thought this mild steel tubing was the same but maybe not. I am not a metallurgy expert.
Just to check, I grabbed new bearings from years ago and put them in the clamps to the same effect as the cleaned bearings.
Thanks for helping me work through it. Will get new tubes during the week and try again.
The rails can have a bend to them, not a big deal, just put the bend, up so gravity flexes it into place. We are worried about the tubing itself being deformed. Without calipers there is no easy way to check that.
Bearings should be grease packed and not spin super freely. So cleaning them out and not re-lubing them could be an issue.
Then the preference is grease over oil for these bearings (for our application)? Most sources for cleaning roller bearings were for skateboards and they used light oil.
If that’s the case I can either pack some grease into the oiled bearings or just switch all the bearings for the unused ones I have. That won’t be the answer but I thought cleaning the bearings was one way to rebuild the MPCNC right.
I’ll keep that in mind. If I have to switch out bearings then I will, but the Super Lube seems to be sticking in there and is made for bearings.
Took the calipers to the gantry rails and found that while rotating the tube in a single spot, the diameter ranged from 25.4-25.6 mm. This was true for multiple points across the entire length. This may explain why all the Z axis bearings don’t make contact either. I tightened the top ones a bit and those are fine, but the bottom left inside won’t touch.
Is 0.2mm within tolerance on the tubes or is it too much inconsistency?
Core clamps. Z axis was a tangent I thought would relate to the tubes.
Should I just build everything up and leave the clamps loose (only tight enough so the clamps don’t move when I try to shake them)? When I was doing it that way with everything mounted, the jittery rail movement was shown by the trucks not staying still as the respective axis moved one way or another.
Here’s a quick video showing what I’m talking about. As I move the core perpendicular that axis’ trucks, the trucks move a bit. This one shows it best.
The first video I took actually showed a new behavior. All of the truck clamps are loose enough to allow the rails to slide in and out since I’ve been taking it apart and putting it back together a few times. The new behavior is that the rail is rotating, which actually seems to smooth things out; this isn’t ideal though since the clamps should be tight enough to stop unintended rotation and keep the rails from moving back and forth (which they do as they rotate). Still, the trucks do show some slight movement by the end of the video (45 seconds).
Core clamps are tight enough so that they don’t move. Tension bolts only hand tight to keep the nut on the end.
Just put it together that all seems right. The bearings track on the rails, inconsistencies, tiny angles whateve,r they will rotate if not secured. Nothing will happen when they are secured, they will track straight. The moving, no worries, the steppers power up and hold it, that is why I use a stepper on each side instead of just one.
Slap the belts on snug things up a bit and start using it. If the bearings all touch you are fine.
