Doing some testing on my (almost totally) complete LR3, and having a few issues. Traced one issue down to the lower bearings on the core not being snug to the rails. Using some feelers, it looks like I have a 0.4mm gap between the lower rail and the bearing. The rails are 3/4" EMT, and I’ve verified I printed the appropriate braces.
HOWEVER - if I drive the core down from x=0 to about x=100, the gap closes up and everything looks good. The obvious assumption is a non-straight rail, but I tried rotating the rails by 180 degrees thinking if I had a low side, that would put the higher side against the bearing and the gap would disappear. But that isn’t true. I’m a bit stumped by this. all the fasteners are snug, and the play is only between x=0 and around x=100.
All suggestions appreciated.
UPDATE: I’ve added 2 photos. Looking from below the beam, if I push in the direction of the red arrow, the core moves in the direction of the green arrow. Out, and slightly up.
The gap I observed is above the lower bearings, illustrated by the red line in this one:
Make sure all your screws for the front strut are tightened the same They dont need to be super tight. One section tighter than another can spread the rails apart
If one or more of your strut braces are not perpendicular to each rail, it could also be distorting the distance between rails. More likely with temporary struts, as the permanent ones would likely self-correct any mis-alignment
If you carefully tighten the tensioning rollers (1/16 turn or less at a time), can you take up the looseness on the one section while not overtightening it for the rest of the rail? (bearings should still be able to turn with some drag).
Try loosing all your front strut bolts. Don’t have to take them out just loose. Then slide the core side to side and see if anything changes. Even with a clutch set they can be tightened to different amount. one brace has more plastic drag than another, one nyloc grabs a little more than another. Really should do that by hand so you can feel for things as it tighten up. I say all of this from experience lol. I did the same as you and had to deal with the issues afterword’s lol.
None of the suggestions worked out. For now, I’ve dealt with this by adding .004" brass shim stock (about 0.1 mm) between the rail and the top of the lower rail clamp as shown:
Probably not an officially approved approach but it seems to work, as the play in the core is gone. And I may now be able to cut something along the Y axis and not have the bit wobble in the first 100mm of travel.
When time allows, I may replace the lower rail entirely and see if that helps. Fortunately EMT is cheap.
Around here the “Officially Approved Approach” is the one that solves the issue. So I’d say if the shim solved your issue than its officially approved as far as I’m concerned
Once I cut the shape out, I’ll put a straightedge on the cuts to check them, but at first glance, they look good - or at least orders of magnitude better!
