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LM8UU x-ends for Prusa by Prusa :-)

by josefprusa, published

LM8UU x-ends for Prusa by Prusa :-) by josefprusa Jul 8, 2011
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GNU - GPL
LM8UU x-ends for Prusa by Prusa :-) by josefprusa is licensed under the GNU - GPL license.

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Summary

I removed the files after seeing new user agreements. I don't like the feel that Thingiverse owns the design. Files are here http://reprap.org/wiki/Prusa_Mendel

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As far as  I can tell Josef Prussa has started his own company based on the open source Rep-Rap and may have a lot to gain if he gets a lot of people to hate his now competitor MakerBot. So think about that everyone jumping on the band wagon to abandon Thingaverse.

I understand your cynicism, but I know Jo is a lot more committed to OSHW than makerblop

I modified this to omit the zip tie holes. I still use zip ties, I just put them around the whole thing.

I found that the zip tie holes created a quite weak place in the part and I had two of the parts snap in half at the zip tie location while trying to insert bearings. I decided that the holes were just kind of extraneous decoration and the zip ties work every bit as well without the holes, and th
e part is stronger without them. Perhaps just a bump on the back corners to give placement guidance would be good.

Also a hint for inserting the bearings - trying to put them in by hand results inevitably (for me) with stressing the whole part since the tendency is to want to hold the entire part.
I got great results by placing the bearing over the correct spot, then using long nose pliers, one jaw inside the bearing and one behind the bearing holder column, then squeeze. This pushes the bearing straight in with no pressure on the rest of the part, and even very reluctant parts will just s
nap right in.

i did the same, had the same problem.

Have you moved these into your branch yet? I enabled the LM8UU setting in the config on the latest felt, but the generated output doesn't look quite right (looks like it has integrated plastic bushings instead of snap-ins for the bearings). I only ask because I'd like to make an SAE version - I'm afraid the 5/16" nuts won't fit these STL files.

Unfortunately, because of the new position of the stepper, the max pulley diameter is artificially limited to somewhere around 15mm. My pulleys are 22mm PD, and the belt rubs on the bump above the lower screw, to the point it is causing backlash and missed steps.

To fix this problem, you either need to push the X motor even farther out, so the two ends of the belt line up with the pulley mounted farther out on the motor shaft, or better yet, just go back to the original motor placement.

I am dubious of the theoretical benefit to this new motor placement.
... The old version had the motor inline with the vertical rod, and opposite the weight of the X rods. This new one shifts all the weight to one side of the axis, with no counter weight to balance it. The rods are strong enough to handle the twisting load the motor creates, but I could definitely se
e this leading to potential binding if anyone has rods that are not perfect. With Printed bushings I suspect this would bind constantly, but the LM8UU's might be forgiving enough to let it work.

I think the column holding the LM8UUs could use a little more material. I've found it really easy to snap the thing when fitting the bearings.

I modified the SCAD and eliminated the zip tie holes. IMO they serve no purpose but to make the part weaker.

See my note above on fitting the bearings; squeezing them in with a pair of long nose pliers did the trick for me after I broke two of these.

I was skeptical about that huge overhang on the x-motor bracket, but cooled PLA never ceases to amaze me :)

Why hang the motor way off to one side rather than keeping its centre of gravity between the rods?

Don't the closed ends mean you need to get the rods exactly the right length?

The motor's weight is directly opposite, and well-constrained by, the bearings. I don't think it will have much effect, and may even help stabilise any rocking.

Re the closed ends, that's what I wondered. Greg's version has an x axis rod adjuster on the x-end-motor, and the x-end-idler is open, or can be closed by adding a couple of bolts. I would have to say it's a bit more advanced than the version in Prusa's felt branch. I downloaded it from GregFrost's github: https://github.com/GregFrost/PrusaMendelhttps://github.com/GregFrost/P... and created STLs from the OpenSCAD files. Greg's linear x-carriage is more advanced, too.

However, the Prusa felt branch has some nice parts - for example, a cut down Z motor bracket, and a beefed up Y motor bracket. I'll probably print those.

The overhang printed fine for me too!

any idea what length the x smooth rods need to be trimmed down to ?

funny, we are using the same linear bearing in a custom made holder that we printed on our 3d printer. But we use it for the mantis cnc milling machine. Will share it soon

I was a bit skeptical about the overhang but it prints fine. :)

The bearing holder was slightly too small and the part broke when I tried to insert the bearing. I'll try to print another one tomorrow.

What is the purpose of the small holes in the bottom? To remove some material to allow the push-fit tension piece to flex a bit more? My SF profile isn't tuned very well for small holes so they're almost nonexistent :(

I think the little holes are there to trick skeinforge into reinforcing the area (they are at the base of the tabs). So the final piece is less prone to breakage. Prusa wrote about this some months ago. See http://josefprusa.cz/selectively-making-parts-of-object-stronger-ohttp://josefprusa.cz/selective...

I confirm it prints without support, but that bridge of near 30 mm is sportsy.

Small footprint, much attention to detail, lots of thought and clever, interesting techniques. Great Prusa vintage!

Whish list:

1) open ends for the smooth rods (allowed adjusting to varying rod lengths)

2) no ridges inside the channel for lm8uu (allowing use of lm8luu too without filing plastic)

3) larger holes for the stripholders (smaller sizes are hard to source, so one tends to do just as os1r1s)

+1 for #1. Open ends for different lengths of smooth rod would be very humane. I already broke one as I was drilling the hole myself. :-[

awesome and timely for me! Can you print this without using supports?

What's the new recommended lengths for the x rods?

Great job! I'll install it at the weekend.

And printed in Gold just for the Bling of it! 8-)

it happens only in the outline in the small holes, ive noticed its in the motor holder in both sides, and in the idler only in one side.

Interesting, what FW are u using? Generally I suggest you to switch to SF40+ you can use my article to ease the pain http://josefprusa.cz/skeinforge-40-volumetric-calibrationhttp://josefprusa.cz/skeinforg...

yeah ive been plaining a move soon, i just got my mendel calibrated so geat im afraind to touch it :).

i have gen3 with makebot fimware 2.9, polulu external driver, sf35 with retract, 1 extra shells, 55mm/se, flow rate 7, sells mendel with mendel parts x axis, and open x carriage , gregs open wade.

im printing with sf35 with 1 extra layer. and on the small holes the extruder goes much faster laying down way too much plastic, i think it a problem in the file, or sf is calculating a longer route or something.

i've been waiting for these, these are the only missing parts for my full lm8uu prusa!!

im already priniting!

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