Printrbot Simple Acme rod coupling

by owens, published

Printrbot Simple Acme rod coupling by owens Jan 9, 2014
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Our Printrbot Simple uses 1/4" Acme threaded rod for the Z axis, and came with a piece of vinyl tubing as a coupler to the motor shaft. Sadly, we lost that little piece of tubing, and this printed coupling is our answer to that problem.


The coupler and nut should print easily without support. Depending on the motor you have the fit on the shaft may be tight; you can either drill out the shaft hole slightly, or if you print the part in PLA heat it with a hairdryer so it will slip on.

If you have a flatted shaft one screw will suffice to hold the coupler in place, the second spot is provided for round shaft motors.

I found that the coupling gripped the Acme rod tightly all by itself, but the printed nut is available to lock things together if needed. I recommend finger tightening only.

If you want to tweak the parts in OpenSCAD you'll need the Thread Library for the Acme screw threads: http://www.thingiverse.com/thing:8793

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Owens you make want to take the longer item down since i could not get it to work. the base is to large and ends up binding on the y axis stepper motor while the z is at the bottom in home position. A new item has been posted /thing:278089 that seems to work well on my simple 2014 that adds more Z travel by replacing the Acme nut with a longer one. Thanks you for modifying the part for me to try.

Printrbot Simple 2014 Z-Ext

this will fit v2 simples correct?

I don't know that for certain; I designed it for our Simple, which is a conversion from the original beta version. It fits fine there, but I don't have any of the more modern machines to test with.

Owens, Have you thought about making this taller so the Acme rod sits higher? i have noticed on my 2014 simple that i have almost 45mm of extra space at the bottom of the acme rod when my print head is as home position. i have extended my Z axis smooth rods but need to find a way to push up the acme rod to gain the extra head room. Sadly tinkercad is as deep as i have gotten so far in producing my own parts and i don't see a way to remix your .stl inside of there. Let me know your thoughts on this subject.

It's easy to change the height by modifying the OpenSCAD code, but I haven't put it in Customizer because it requires the screw library and I'm not sure if that would work. I'm uploading a long version that's an extra 20 mm taller; it already uses up about 5 mm with the transition from the motor shaft to the Acme thread, and another 14 mm or so between the threaded section of the coupling and the lock nut, so that should use up most of your 45 mm - unless you meant that you had 45 mm even with the coupling installed, in which case we could try stretching it further. I'd start worrying about wobble at some point though. If you try it, let me know how it works. . .

Thank you Owens so much. I will download and start printing once the item on my build table is complete (in the middle of a long print now.) i have downloaded and opened your original .scad file but not matter what number i tried to modify in openscad i just could not seem to stretch the item longer. I guess there is a reason i am a network person and not a programmer. I will find some tutorials for openscad now that i have it and am starting to understand a little how you constructed the model in side of it. I will upload pictures of the stretched item and give you feedback. i head out on vacation at the end of the week so it may be 2 weeks before i can update. thanks again for the help

I got the longer part installed last night but sadly the base is to large and at the bottom of travel it Binds with the Z motor. Sadly my part did not print out with the acme threads straight either so i had a little wobble. It did push up the Acme rod and added more Zaxis space but at the home position it pushed the Y carrage over since it moved the zmotor. i will get pictures up for you to see. thanks

I really like this design but when i thread my rod in it is way crooked. Of course i suppose its possible that i messed up the alignment when i was trying to get the nuts into place. Any suggestions for that because it was very tight and i almost didn't get them in place.

You mean that the Acme rod is crooked relative to the coupling, right? But it's also tight fitting into the threads? I wonder whether the end of your rod was messed up when it was cut to length at Printrbot. It's easy to ruin the last turn of the thread, or leave a partial turn that won't start into the nut properly. It's hard to describe what the end should look like, though you can look at a manufactured bolt for an example of how the thread should start. If it doesn't look like that I'd suggest cleaning it up with a file, or a grinder if you have one (but be careful holding the rod so you don't damage it in the process).