[Mendel Z-Axis Mechanics] How could... wasn't supposed to hold?

I'm starting to wonder what went wrong. Just when the motors were starting to work, things begin to fall apart.
Now, how much strength the Z axis is actually supposed to hold?

The thing that triggered it all was the Z motor turning and not being able to pull the belt... so i got there, screwed even more the holder in the gear, screeching it slightly... not really a problem in theory... but when began to test the turning by hand again (so not even by the motor) the thing in the photo began to just collapse:
[picasaweb.google.com]

So now I'm wondering... how much actually, by design, the Z axis is supposed to hold?
I'm beginning to understand why prusa has dual motors now...

Now I'm not entirely sure how to progress on this...
Build that piece by hand? Order another?
Dismount everything and remount Z axis? I find it strange that it needs *so* much strength, maybe there's something in the bars?
Use a custom modification with dual motors for a Z axis?

One thing is sure: can't print anything yet, so it'll be hard to have new spare parts easily.

The Z lead screws should turn easily and that part should be easily strong enough for any amount of belt tension. Not sure what is wrong.

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[www.hydraraptor.blogspot.com]

Well it seems few parts are slightly hollow.
And one of them (the Z opto holding) was already bent/partially broken when arrived at me.

Is it possible that they've been printed cheaply? Meaning, trying to save plastic in putting less material inside?

Edit: seems like the material from where i got the parts might have been strange or not really strong:
[lh3.googleusercontent.com]
(notice the part on the right border of the image)
So far it seems that hypotesis gets confirmed. Do exist very cheap plastic types or ones that are mixes in a way to obtain decadent material? I know PLA is a mix between two substances...

Edited 1 time(s). Last edit at 06/29/2011 03:29AM by Kiantis.

It looks like you overtightened the bolt.

Used a double big washer to make it stand on the divelted piece better:
[lh5.googleusercontent.com]

Also resquared again axes and now the turning is somewhat smoother.
Tested motors, all seems ok, for now.
[www.youtube.com]

Is it normal that the Z axis do all that noise?

It's hard to tell how load the noise is from videos. But if you're referring to the rubbing noise when the z-axis was moving, I think that might be the belt rubbing on the plastic gears on the end of the threaded rod. If you look at the pulleys, you might see some wobble. I also had this problem. I got rid of the noise by lubricating side of the belt with silicone grease (plumber's grease).

I think I found out the problem in the end.
The fact of having a very resistent Z axis was due to the screwed bars being slightly deformed. So each time they turn they rotate widely in the top...
This means that at different heights the distance between the two rods is slightly different by maybe few mms, for now I've managed to let them loose a bit (unscrewing some bolts that keep them still) so that they aren't excessively tight, but I need to find a better measurement/distance to keep things aligned. Maybe resquare the axis again... when I did the first time I actually discovered the Z axis was moving smoothly like I could turn the gear with just two fingers. Before that I couldn't turn them without even two hands in certain points, had to use a wrench.

Maybe also lubricating the screwed bars could help..

You should be using extremely straight A2 threaded steel bars for the Z-axis drive.
They must be exactly parallel and then you shouldn't have any problems!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Well Well, I did some hacking on the piece.
I've removed that excessive plastic part and made it all flat, then used another big + small washers to create spacing from it...
It seems that using a big washer to hold on the plastic gives even more stability.
So sorta solved it, except for the deformed bars, which I'm still not sure what to do with them... maybe smash them a bit with a hammer... eheh.

So if someone should happen to encounter this unlucky outcome with breaky plastics, that's how I solved it, and I hope this trick could prove useful too in the future?

[lh3.googleusercontent.com]