Tube OD a little big

Hello all,

So a little backstory: I started on this project a couple of years ago, printing all the parts (25.4 J set) and getting some nice stainless tube cut to size (1.000 X 0.065 (ORNAMENTAL) ST 304 TUBE ROUND from Things sat for awhile until moving a few months ago, saw the new Burly parts, printed those, procrastinated a bit until self-isolation projects brought me back to this. Started assembling, and things were a little tight, but came together.

The rollers all roll, but not nearly as smooth as I’ve seen from others. They take a good bit of force even fully loosened but I figured it just needs to break in. However, I can’t get the center gantry square, no matter the combination of loose/tight on the bolts shown in the instructions. On a hunch, I finally bought a nice pair of calipers, and my tube is 25.8mm OD. My question is, will I be able to finish this build and be functional as is? Should I reprint 1.5% bigger? I really don’t mind reprinting if it will make things work better, but the last thing I want to do is try and source new tubes. Any other suggestions on how to proceed?

My first mpcnc was a little tight, too. Definitely took more than 1 finger to push it around. After running for a while, it loosened up. Probably the bearings wearing flat spots into the tubes.
Since you have it mostly together, I’d say run it. If you really want to make sure before you put anything valuable underneath, you can write a quick gcode snippet that sends the center from 0,0 to xmax, ymax and back, then copy paste that a few hundred times. Takes less than a minute, start to finish, if you stop every once in a while and copy bigger chunks. Might even be able to get into the thousands, but that’s silly.

Let it run, remove the belts, then see how it feels. If you like it, put the z in and carry on. If you don’t, reprint.

If it were me, though, I’d probably just go for it.

Thanks for the input. I’m wondering if reprinting 1.5% bigger will have any impact on the motor mounts or any other critical dimensions, or if there is enough slop in those to not worry? Also, if there are certain parts that wouldn’t really benefit from a reprint if they fit “good enough” ie foot. I only hesitate as @vicious1 has separate versions for 25mm and 25.4mm, so my extra .4mm could actually be a problem?

You wouldn’t want to reprint at 101.5% because you’re not scaling the bearing also, so you’d probably end up on the too loose side Instead of too tight.

If running it doesn’t do much to free things up, maybe egging the holes in the plastic for all of the bearings out by .007” or so with a round file of a similar diameter might get you there. Obviously you’ll only want to open the one side of the holes to allow the bearings to move farther away from each other.

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Only thing likely to break is the plastic parts, so you don’t really have anything to lose except some time, right?

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That’s a good point. That will probably be the best fix.

Thanks @blainesgarage and @turbomacncheese for your insight.

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