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Linear Rod Adjustment Mechanism?

Posted by Trakyan 
Linear Rod Adjustment Mechanism?
April 10, 2018 12:13AM
I'm working on a 3D printed CNC project, and given that the components are all 3D printed, I'm wanting to design adjustment points into the parts to let the user correct for print inaccuracies. One place where I'm a bit stuck on how to do this is the Z rails. They're end supported between two plates. I need some way to adjust them where they are end supported to let the user make sure the rails are parallel to each other, and orthogonal to the other axis. I've considered using two set screws offset by 90 degrees to let me nudge the ends of the rails in X and Y which would accomplish what I'm after, but doesn't seem very elegant.

Anyone got any other ideas? Eccentric bushings seem like another idea but they don't let you shift the rail end in just X or just Y so they'll make getting things square and parallel difficult in some cases and impossible in others.
Re: Linear Rod Adjustment Mechanism?
April 10, 2018 01:39AM
Long holes for one direction and shims for the other. That requires a baseplate/bearingblock design.
Re: Linear Rod Adjustment Mechanism?
April 10, 2018 02:18AM
Could you clarify what you mean by baseplate design? The design I have in mind will be a flat plate with through holes for the rods to go into. Plain old shims could actually work really well for this, I can't believe I didn't consider them. The plate they're mounted to is held down at three points, so I've thought about using those like leveling feet to get the rails orthogonal to the other axis.

I think I'm giving up on anything particular for adjusting parallelism (maybe just leave it to shims) and relying on most 3D printer being able to repeatably even if not accurately reproduce a hole spacing. I'll be using hardware store steel tube for my rails so getting them super parallel is a bit of a pipe dream.

I guess there are a lot of options I'm just trying to find the most elegant/simplest.

EDIT: my one gripe with shims is that you need to do a fair amount of disassembly to get them in place, then tighten everything down to check if the shim is a good size, rinse and repeat. I'm trying to find a more "turn key" solution, like tighten/loosen one bolt to correct for tilt in the axis this way, tighten/loosen another bolt to correct for tilt in the axis the other way and done.

Edited 1 time(s). Last edit at 04/10/2018 02:24AM by Trakyan.
Re: Linear Rod Adjustment Mechanism?
April 10, 2018 04:20AM
The base plate would be your anchor point and the long hole ( or oval hole ) could simply be a bigger hole to adjust the bearing block in XY directions independently. No more shims needed, just use bigger washers to cover the bigger mounting holes.

Edited 1 time(s). Last edit at 04/10/2018 04:40AM by o_lampe.
Re: Linear Rod Adjustment Mechanism?
April 10, 2018 04:44AM
Ahh, I see what you mean. I'm trying to minimize the part count so I'd prefer to find some way to do it with just the main plate.

EDIT: I think I should clarify, the rods will be supported by two plates, one at each end. The problem I guess I'm having is I planned to use the three mounting points of the plates as leveling feet, however with two separate plates this becomes complicated as they wont rotate/twist around the same axis as each other when their individual leveling points are adjusted and I don't know how this would affect the adjustment.

Edited 1 time(s). Last edit at 04/10/2018 05:05AM by Trakyan.
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