Kossel Mini Problem

Ok, so this apst week I decided that I would start building a Kossel Mini printer. I printed out all the parts on my Prusa Mendel and order the Open Beam and various nuts & bolts. Yesterday I started assembling the frame. I got it all together and it looks good except that when I lay it on its side, there is a considerable amount of wobble (~3 mm) diagonally (as in corner to corner - like a desk with legs that aren't the same length). Something is not square and Im not sure why.

Could it be because of my printed vertices? I ran into some warpage problems when printing them. The warping is on the "legs" of the parts so I thought it wouldnt affect the uprights, but maybe it does?

Has anyone else run into this problem before?

Any help would be appreciated.

Thanks,
-Lucas

maybe you can resolve this by loosening the bolts, correcting the stand and fastening them again. I had mine fixed in wrong positions first, too, but after some measuring (be sure to measure the diagonals, too), it worked out quite ok.

I tried loosening all the bolts and setting the whole thing on a flat surface while I tightened them back up right when I noticed the problem. It helped quite a bit (as it was very far off at first) but when I tighten them again it goes back to the 3mm wobble.

I havent tried measuring anything though. That seems like a good idea. What measuring should I do? Just on the the base and make sure all are equal? or what?

Thanks

Hi,
measure the distance from bed to top on all 3 rods, it should be almost the same (it's not THAT critical, when you're calibrating, the endstops set the correct values). And then measure the diagonals (from left rod bottom to right rod top and vice versa). This should be the same everywhere, because it ensures that the angles are correct (90° ;-)).
I've found the kossel to be very rigid, regarding the small parts used. But if it isn't in your case, maybe you can span some wires between the rods (again from left top to right bottom and so on), that would get you a lot more stiffness.

Just to clarif, the problem isn't that the frame isn't tight. When everything is tightened down it is rock solid - just not straight. The lengths of the rods are all the same, but something apears to be twisted. It's like the top triangle and bottom triangle don't want to line up right. The top one is rotated a few degrees from the bottom. This is what causes the wobbling that I was talking about when it is on it's side.

What would this do to the print if I can't fix it? Would it make the print have the same type of twist?

-Lucas

Quote
Localvsc
What would this do to the print if I can't fix it? Would it make the print have the same type of twist?

If the twist is bad enough you will not be able to level the bed to even lay down the first layer.
The error will be more complicated than simple twist of the printed parts.

Ok that's what I was worried about.

However, I just spent about an hour re-doing everything and thinking it through carefully and I might have found the solution.

I used some extra printed top vertices that I made and some extra open beam to make another top frame triangle piece. I slid down the existing top piece so that it was touching the motor mounts / bottom frame pieces while everything was loosened. I then added the new top frame (which was already tightened down) to the top and went around side by side tightening the bolts while the whole assembly was sitting on a flat surface. Then I slid the original back into place and removed the other.

It now seems to be lined up well. I don't notice the wobbling/twisted issue anymore. Hopefully it will stay that way as the temperature and humidity change...

-Lucas