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Printrbot Talk Forum • View topic - Z Axis Couplers on old Plus

Z Axis Couplers on old Plus

Talk about modifications to the printer

Z Axis Couplers on old Plus

Postby RetireeJay » 2018-Feb-Mon-20-Feb

This may be applicable to other Printrbots from the 2012 - 2013 era.

I have a new Prusa MK3 on order, and in order to prepare to make a comparison with my existing Plus, I decided to print a Benchy. One thing that I noticed was that in some parts of the Benchy there were irregularities along the Z axis - where a wall or corner would be wavy in the Z direction instead of smooth. I played around with "the usual suspect" - namely the number of microsteps or full steps per layer in Z, but making these changed did not improve the appearance of the result at all.

Upon closer examination, I realized that the variations matched the pitch of my Z screw exactly (18 turns per inch). So this made me wonder if my couplers from the Z motors to the threaded rods were at fault, like not perfectly concentric or somehow causing slight unintended vertical motion superimposed on the desired motion. Using my dial caliper, I carefully measured the Z motion every 0.1mm for 3mm and compared the actual size of each step to the theoretical size of each step. I found that there was, indeed, a once-per-revolution pattern of going above and below the ideal step size.

So I designed and printed new Z axis couplers.

I was surprised when I disassembled the original couplers to see how the vinyl sleeve on the motor shaft was such a poor choice to establish good concentricity.
OriginalZ_Coupler.JPG
OriginalSleeveOnMotorShaft.JPG
NewZCoupler_1.JPG
NewZCoupler_2.JPG

After the upgrade, the standard deviation of the motion in the Z axis was roughly cut in half.
PrintrbotZIrregularity.JPG
And Benchy looks better, although still not as good as I'd hoped.
Benchy.JPG
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3, upgraded to MK3S
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Z Axis Couplers on old Plus

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Re: Z Axis Couplers on old Plus

Postby Mooselake » 2018-Feb-Wed-13-Feb

I used the so-called , Lovejoy couplers here in the states. Mine came from eBay iirc. Prior to the purchased ones I used a (not sure if that's the exact one I used, thought I'd posted some pictures but can't find them), not sure if the fancy aluminum and red plastic version was any better.

Kirk
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Modified KickStarter Classic Plus 7/2012
KS Thingybot Delta Pro 10/31/16
Creality Ender 3 Pro 12/2019
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