Prusa Z Screw Isolator

by DaleDunn, published

Prusa Z Screw Isolator by DaleDunn Mar 27, 2012
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This little bracket allows the Z axis screw to wobble without influencing the position of the nozzle. The Z axis nut iss captured in a bracket that is not rigidly coupled to the X end brackets as with the regular Prusa.


If you built your Prusa without the upper Z axis nuts and springs, you can lift the X axis off of the lower Z nuts to install these. If you have the springs, you'll have to back the Z axis screws out of the X axis. If you want to keep the springs, you can install a second pair of these above the X axis.

As pointed out by Buserror in the comments, you will need to make sure you have enough room in your X ends for the movements of the screws. I found when assembling my Prusa that the threaded rods themselves are abrasive enough to widen a hole in ABS parts, if used as a file. So, if you don't have enough room for your Z wobbling screws, you can use them to open up the hole. Or you could possibly straighten them enough by hand to avoid interference. Either way, make sure you have enough clearance.

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Forgive me but isn't this just the same as sticking an m8 nut on I cant understand how this can work

Normally, the M8 nut is captured by the X Ends, so any wobble from a slightly bent screw is transferred into the X axis rails, which causes wavy prints. These adapters capture the nut in the same way, but sit underneath the X Ends with no mechanical connection to them. That way, the adapters can slide around under the X Ends without transferring wobble into them.

Properly straight screws are a better solution, but not as easy to implement.

Improved printing quality a lot!

Is there a 5mm version?

Check out the remixed one. http://www.thingiverse.com/thing:45454

Parametric Prusa Z Screw Isolator
by llluis

I gave this a shot. It helped my wobble some but didn't get rid of it.

You probably have some slop on your smooth rods, or you may be seeing some of the banding I linked to in a G+ discussion in another comment.

I don't think it's bandy. The piece fit rather snugly on the smooth rod. The wobble is in the same pattern with or without your mod. It's just that with your mod it isn't as pronounced. This makes me think there is something else wrong with my printer. (it an i2 btw)

A note on long-term usage: Have some spares on hand. I had a set of these split, apparently from exposure to the oil I used on the threaded rod. Material was Protoparadigm ABS.

Model has holes, doesn't slice without massaging.

Made a huge difference in print quality. Thanks!!

As pointed out by Whosa whatsis on a G+ thread, this will eliminate Z wobble but introduce a small error in layer height. See here: https://plus.google.com/u/0/105535247347788377245/posts/Lm87MYow8TWhttps://plus.google.com/u/0/10...

Hmm. The G+ link seems to have gone dead. Anyhow, the gist of the conversation was this: These isolators will minimize Z wobble artifacts, but in doing so, introduce another smaller effect. The wobbling screw causes these to turn the nut slightly, raising or lowering the Z axis slightly. So, these don't get rid of Z wobble, they reduce it to be invisible under whatever else the printer has going on. If you are pursuing the highest print quality, you have to properly isolate Z from the screws: more complex isolation that doesn't turn the nuts, straight screws, more rigid guidance, whatever your machine needs.

Printing one now, had to use netfabb to repair the part though. Love the simplicity and effectivity of this design! Good job! :)

this wont slice not sure what to do?

Not sure. Try a different slicer, maybe different settings. IIRC, I used SFACT when I printed these. So, that or Skeinforge should slice it. For a less-forgiving slicer you may need to shove it through one of the on-line .stl repair services whose names escape me at the moment.

I just printed a pair of these and the M8 nut fits perfectly, but the other end seems a bit small for the smooth rod. It seems to me that it should barely touch (just enough to keep the nut holder from rotating).

Anyone running these yet? Do yours grip the smooth rods at all?

As the software support people say, it's working as designed. Mine do grip the smooth rods a bit, but not enough to cause any problems with the Z axis movement. My thinking is that this is a better option than designing for a little slop, because, well, slop is slop, but you can always sand off a little material if it grips the smooth rods a little too tightly.

I sanded them down just enough so that there was little resistance when sliding up and down on the smooth rod.

Unfortunately this hasn't solved my slight banding issue, which means it is probably slop in my X and Y axes :(

One thing you need for these to work well is to make sure the hole for the threaded rod in the X mount is wider by a margin... otherwise it still catches the rod as it goes up/down. If it's wide enough, it won't touch the rod and will be held only by the linear bearings.

There is something of a non-wobble discussion going on in hte RepRap forum right now at http://forums.reprap.org/read.php?1,126468,126877#msg-126877http://forums.reprap.org/read....

Perhaps you can lend or receive some insightthere?

This solves potentially /two/problems. On my printer the X sometime get caught on the threaded rod when going down, and if the nut escapes, the leveling is totally BEEEPed. This little piece keep the nut in place, so it won't happend again!

And if it removes a bit of wobble. all the better :-)

You got it! =-O

I searched very long about a way to decouple the X-carriage from the Z-axis screw to eliminate wobble.

This is so simple but should work reliable, I love it.