z-gauge knob for Printrbot Plus and Prusa

A mod I made on my Printrbot Plus 3d printer has made my printing life a lot easier and free of print-run first-layer headaches, and I'd like to share it for others to replicate. It's worth the effort.

It basically involves putting a 200-guage knob on each of the two z thread rods. The knobs serve two purposes:

1) stabilize the z thread rod, which if slightly bent dances in circles near the top that can cause one of the z stepper motor to jam and ruin an otherwise good z calibration. This is specially a problem with Prusa printers.

2) allow last minute changes to the z levels to match both the left and right z thread rod levels. You... Start the print; pause the print immediately after the z-stop has been detected, turn the z-gauge knobs to the desired levels (if necessary), and resume the printing.

This mod can even allow you to use a different print bed plate of varying thickness on-the-fly since you can change the height of the z just before actual printing resumes. You know the pitch of the thread rod, so you can calculate the height difference per step or thread rod full turn.

My apologies for the poor photo quality...
P.S. I'm quoting my shared post in Facebook verbatim which I made a few days ago, but I really wanted to share this here in reprap.org since this is where there probably has a bigger number of people who might be interested.

Edited 1 time(s). Last edit at 01/11/2015 08:34AM by Roi Igarashi.

Constraining a bent screw at the top will force it to wobble in the middle...where the nut usually is. This has been known to cause Z axis banding on prints. No problem is solved by constraining the top and only serves to make it worse. I don't know how you came to the conclusion the letting the screw move freely at the end causes a Z motor to skip, if anything it would be worse when constrained because there is now resistance to rotation.

Edited 1 time(s). Last edit at 01/22/2015 09:53AM by tjb1.

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