Homemade Blv Cube

doublec4

The three purple printed parts now have standard 8mm leadscrew bearings inside. I bought std flange bearings and used just the bearings - which I stuck in the purple caps so they wouldn't be as constrained as the steel flanges. The purple caps shown here were temporary while waiting for the bearings.

They just stop the top from bouncing around when the leadscrews turn. There was enough of an angle in one leadscrew connection that at the lowest Z the top of the screw would bounce pretty badly and shake the printer when rotating quickly. The bearings calmed it down substantially.

I had similar alignment issues with my Z rods on a different machine (old Rigidbot printer). If it is of any value to you, here was my solution that nearly eliminated my z wobble:

https://www.thingiverse.com/thing:3821853

Rather than constrain the top of the Z rod, I think it is important to allow it to move freely. By constraining the top I believe you are introducing more deflection to the middle of the rod where you bed is connected. First and foremost you need to make sure your z rods are as straight as they can be, and beyond that, I would try and put some adjustability into the z stepper mount such that you can find the "sweet spot" where the mis alignment is minimized. In that link I posted I had typed out a sequence whereby I ran the bed up and down with the z mounting screws loose and then tightening them to ensure the best alignment I could possibly get.

markz

@doublec4 Yeah, I agree with the trying to get it straight thing. I think the top caps are pretty good about not inducing wobble since they can flex a fair amount. When I put them in place the entire Z lift/lower operation went from wack-wack to whisper quiet and smooth.

But... they're not the best possible solution.

I did try multiple times to align the screws, first. It's incredibly difficult to align almost anything on the BLV cube. There's not a lot of play in the metal Z mounts and screws are hard to get to.

I ensured the rails mountings were as straight as possible. I first replaced my original flexible Z couplers with printed rigid couplers - which helped a lot - but didn't entirely remove the oscillation. Thanks for the link.

It's worth reading this: https://www.steinmeyer.com/en/technology/speed-limits/critical-speed/ which discusses how adding a bearing quadruples the critical speed for the leadscrew.

dhusolo

I have printers with the top of the lead screws constrained and not constrained. It depends on the lead screw and the setup. If the lead screws are already slightly warped which is not uncommon constraining the top can cause more issues. If they're straight and you line everything up correctly you'll be fine with constraining the top