Prusa Lower Z Axis Mount

by AlephObjects, published

Prusa Lower Z Axis Mount by AlephObjects Jan 17, 2012
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Prusa Lower Z Axis Mount by AlephObjects is licensed under the GNU - GPL license.

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After building a MendelMax and seeing the extra stability from using a bearing to hold the bottom of the Z threaded rod we decided to add a similar part for a Prusa Mendel.

We've done testing and it seems to work really great for reducing Z wobble. If you have any suggestions or findings from testing please leave them in the comments.


This mounts similar to the existing structure except for a few changes:

-The bottom center horizontal threaded rod needs to be cut shorter to 295mm
-Also the two Z drive threaded rods need to be at least 295mm.
-Two 608 bearings are needed to hold the Z drive threaded rod on the bottom.
-You will need two M8 nuts tightened together on the bottom of each Z threaded rods. This sits on top of the bearing.

The clamp is the same Prusa rod clamp used on the Z motor mount. So, you will need two extra rod clamps.

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I made a "clamp" part for this nice mount - but haven't printed it yet. -> http://www.thingiverse.com/thing:208878http://www.thingiverse.com/thi...

Prusa Lower Z Axis Mount Clamp

do u have the "clamp" part? O:-)

The clamp is the same Prusa clamp for the Z motor mount. You just need to print two extra. Thanks for pointing that out though. I'll add it to the description.

Aah great, as i hoped. :)

So this just sort of rests on top of the bearing? Is there any reason not to clamp the rod to the bearing inner race by putting a nut on each side of the bearing?

Funny, I made a similar thing (didn't had time to post it)! Your's is nice.

And I agree, it improves a lot the Z axis (mine was always falling down, due to slip on motor shaft).

Now I plan to put the motors at the bottom, maybe by using the top part, and make a new one there (with a bearing).

Heh, maybe you could just take the original mendel parts which have the z motor mounted at the bottom. Only problem is there isn't enough room to straight couple the motor shaft to the z-rod, so you have to put the motor upside down and connect it with a belt and a pulley. I would definitely be interested in some new hybrid sells-prusa z rod ideas.

You don't need anything too special to run your motors from the bottom. I should know, I have my Prusa 'the wrong way up'! However, I use some short NEMA17 motors - Z axis doesn't need much power anyway - an extra bar at the bottom for the motor mount, and the Sells Z-rod clamp at the top. Also, bars at the bottom need to go over the bottom vertex rod. See here: http://dl.dropbox.com/u/709557/Reprap/IMAG0106.jpghttp://dl.dropbox.com/u/709557...

At least I don't have to worry about pushing down on the extruder breaking the z-motor-couplings!

Doesn't that still put all of the weight of the X axis on the Z motor shaft which can still cause wear on the motors?

I suppose ideally you would want a support for the leadscrew that wasn't through the motor shaft, like a motor coupling that took the weight on a bearing with thrust washers each side of it, like in the CNC world. But we're not dealing with particularly heavy loads, and it's not moving most of the time. The advantage with motors at the bottom is that the support the motor leadscrew solidly from underneath, though I haven't done this properly yet.

I've just realised that this thing does exactly that, sorry! It provides vertical support of the x-axis at the bottom, takes pressure off the motor bearing, as well as guiding the rod. Ideal! You could further improve it perhaps, by making it footed, to directly support the rod on the ground.