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Bar Clamp - Twist-On

by hairy_kiwi, published

Bar Clamp - Twist-On by hairy_kiwi Nov 25, 2012
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One of my Prusa Mendle Y-Axis [Smooth] Bar Clamps cracked as a result of it being slightly over-tightened while building my printer. The printer's been performing just fine, but I recently I wanted to upgrade the Y-axis PLA bushings to LM8UUs and,
a) didn't want to risk the cracked bar clamp failing completely during upgrade, and
b) didn't want to start tearing the whole printer apart for the sake of ONE bar clamp.

So here's a bar clamp that:

  • is easy to retro-fit without disassembling your Y-axis,
  • has a 'developed' surface, (vs a simple hole) to clamp around the smooth rod, which together with the clamp arms being wider at their base, makes this clamp almost incapable of being overtightened,
  • has an 'anti-twist' tooth and socket feature which positively locks together the clamping 'arms' during installation. This effectively prevents the outward displacement of the clamping arms that otherwise occurs when tightening an 'asymmetric style clamp' such as this.

Mating 8mm threaded and smooth rods. (Prusa Mendel, etc)

Compared to the standard Prusa Mendle Bar Clamp, the distance between centres of the smooth and threaded rod will be reduced after fitting the version 9-0-X of this thing. Two further versions exist which will be finalised and uploaded when I get around to it: 9-1-X and 9-2-X which provide approx 1 and 2 mm extra separation respectively, between threaded and smooth rods.

-X only denotes 'plain' (-0) or 'chamfered' (-1) corner on each of the clamp arms.

This is a work in progress only in that the 9-1-X and 9-2-X versions are not yet complete; 9-0-X is fully functional.




  • Compared to the standard Prusa Mendle Bar Clamp, the distance between centres of the smooth and threaded rod will be reduced after fitting Bar Clamp - Twist On v9.0.X. Two further versions exist which will be finalised and uploaded as time permits, 9.1.X and 9.2.X which provide approx 1 and 2 mm (respectively) extra separation.
  • Test printed/fitted in PLA only. ABS should also be good, if not better.
  • A unit piece has been tested to failure and experience would suggest that it's more than capable of replacing an original Prusa Mendel Y-Axis bar clamp.

Derived from: Prusa's bar clamp.stl



  • Designed for 0.3mm layer height.
  • No extra support structure should be necessary.
  • Print, trim off the built-in support leg, debur the clamping surface and edge of the hole which mates with the smooth rod and fit.


  • Gently ease apart the clamp arms as the clamp is pressed (eased) onto the threaded rod.
  • Try to prevent the clamp snapping onto the threaded rod as the 'anti-twist' tooth passes over the threaded rod. This should help prevent any shock-induced delamination.
  • The part should then twist into final orientation quite effortlessly.
  • Tighten the M8 nuts (with penny washers fitted) slowly and smoothly until the anti-twist tooth is completely and positively engaged in its opposing socket.

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I don't normally comment on design but I had to give you some credit here. I thought there was no way this would actually work but I printed, cleaned up and installed and am very impressed. Nicely designed. A very ingenious solution to a real problem. Many thanks.

Hi Mozak, Glad to hear it was useful. Thank you for your kind words and mini-review. :-)

Hi, I really like your design, have you eddited the versiions with greater distance between the rods?

Thanks for your feedback - much appreciated :)

I never did develop this thing beyond the files available; it (still) works as intended, so I lost interest, sorry.

If you wanted a model with greater inter-bar spacing, I'd recommend having a go at recreating it using a parametric CAD tool like OpenSCAD, CadQuery or Fusion360. I might have a go in some spare time, in the next month if that's of any help?

i wouldn't dare to make these in OpenScad :D with a graphical editor maybe.

I think the longer ones are interesting so you don't lose any printspace in height.
at the moment my goal is to maximize the height (http://www.thingiverse.com/thing:22887)

for now I will try these http://www.thingiverse.com/thing:5786

Loches Z Axis Upgrade for MakerGear Prusa Mendel
2-way Prusa bar clamp