Prusa I3 Hephestos improved Z axis brackets

by Oneira3D, published

Prusa I3 Hephestos improved Z axis brackets by Oneira3D Oct 26, 2014


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An improved version of upper Z-axis bracket for Prusa I3 Hephestos.
Using ball bearing reduce swings of Z-axis jackscrew and improve printing precision.


You need two ball bearing 10x5x4 mm (outside diam. - inside diam. - height) or two 10x5x5.
Insert ball bearing in the biggest hole (help with a flat screwdriver into printed crack).

Mine printed with Cura: layer: 0.2mm - sheel 1.2mm - bottom/top thickness: 0.6mm - fill: 40%


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Can you share the source for these? I'd like to use them as base for a customization I have in mind...

Thinking about KP08 bearings ?

Just an FYI if your in to RC the traxxas axel bearings are the correct size for this mod :-) so check your parts bins !

Also after roughly 10 hours of printing with this mod prints are actually better quialty then without ...... In my case anyhow

Be careful. Unless you have anti-wobble installed on your x-ends, this mod will actually make the axis LESS STABLE. All threaded rod is inhearently bendy. There is good reason that Prusa designed the z-axis threaded rod to be free spinning (no bearing) at the top; the reason is that if you bind it at the bottom and the top then the wobble from the bendy threaded rod Must be expressed as movement in the middle (aka at our x-ends). If you leave it opened, as intended, then the wobble will be expressed at the top of the threaded rod instead, and is less likely to affect print quality. Basically, you dont want the threaded rod to fight the smooth rod for control of linear motion. Chromed smooth rods are accurate... threaded rod is not.

finally somebody managed to explain to me why this is a bad idea thank you sir

Hi. Great addition. Would you please add a solid file to include in my customized 3d printer I am working on?

Maybe a step file? Or the original format file.


Excelent, just what i was looking for, much tidier, cant understand why this was not done in the original machine and future ones, just printing them now, thanks for the files.

Gives more stability to the axis X. Thank you !!

This will reduce the quality of your prints, not increase it. You need to leave the end of the rod free to swing, because if the end of the rod doesn't move, the center of it will, which means that your whole axis will shift around from layer to layer as you print.

i'm glad someone brought this up. What would be the next step aside from helical aluminum couplers? lead screws? better frame/tolerances in general? I would assume that lead screws may still benefit from the helical couplers...

This is not true with a 5 mm threaded rod on the z axis. It flexes much easier than the 8 mm guide rod so the x axis is not influenced by slight wobbles in the z rod. This is even the case with slightly larger threaded rod. I used 1/4" rod on my Mendel Max and found the prints to be slightly better with the free end constrained by a bearing compared to when I pull the bearings out.

My best layer to layer consistency actually comes when I put the rods in slight tension.

Thanks for putting this up. I'm building an I3 for someone and was thinking about designing something like this. The free end in the standard designs always concerned me. Maybe I'll just use yours.

Sounds like your real problem is with your couplers. They need to allow the rod to wobble without creating any vertical movement of the entire rod. I find that the helical aluminum couplers are particularly bad in this respect.

I still think it becomes a trade off when the rod diameter gets smaller and the threads get finer. thinner rod with more steps/mm = more flexibility and higher rpm = more end whip on an unsupported lead screw, especially when homing the z (which doesn't affect print quality I know). The print quality differences I speak of are very very slight and only start to appear at about 5 mm/sec z travel rate, and only when the end is unsupported on my machine. That speed also requires too much current for my steppers so I run slower anyway. I do have a very slightly bent threaded rod on one side but normally I see no effect on my prints. layers are directly above each other and identical in thickness.

The ends of the rod whipping around does not affect print quality because your Z axis shouldn't be moving while a layer is printing. Even if you're using platform compensation ("auto-leveling", and you shouldn't be using it), your platform shouldn't be so far from tram that the screw has to spin more than one or two full rotations as you cross the platform, so the centrifugal force would be negligible.

I'm in agree with you, but i can see an improvement in printing quality that i can't explain.
When I replaced again with original pieces printing quality was lower again.
maybe it depends on many factors

I am about to test this piece, i dont know who is right in this discussion.
I do know that this piece will improve x axis stability ( not because it holdes the rod ), wich should lead to a slightly better print. Maybe that's the improvement boeing 787 has.
But that would still not prove that keeping the rod tight is better.
I will test it however

Test is best. The situation may vary from case to case i think!