That Z Wobble

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dognotdog
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That Z Wobble

Post by dognotdog »

After a fair bit of tinkering, I managed to reduce the wobble by quite a bit, like so, before and after:
Image

Note it's not the same layer height, but I think the effect is clear. Also notable on the left piece is formerly large backlash in Y.

What I did to improve things was to remove the upper bearing block on the Z axis, and move down the bed as far as it would go. Then I turned the shaft, watched which direction it bent to, and tried to manually unbend it with fairly good success.

The second step was to put the bearing block back without the bearing, and to move the Z rails so that the shaft ended up in the center of the bearing block, with the Z axis as high as possible while still reaching the bolts in the rail. This is quite a tedious procedure, and it I couldn't get it quite perfect, but overall a big improvement over the untuned state.

However, the Z wobble is still visible, and the print is not as good as guillaume's production parts. Any more tips on how to improve it?

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gfeliksdal
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Post by gfeliksdal »

Hi Dognotdog,

This is how I tune it.
1. Make sure the curved washer is mounted at the bearing on top and also underneath the bolt which is there to fix the coupling. This will compensate for any imperfections of the bolt. I experience that the top or bottom surface of the bolt is not always perfectly flat. When you tighten the bolt against the coupling you are forcing the coupling a little out of line. Don't over tighten it, because that will loose the compensation effect.
2. Make sure the top part which holds the z-axis spindle is mounted firmly. Any deformation or imperfection on the top part is transmitted to the bed.
3. Make sure the spindle isn't screwed in to the coupling fully.
4. loosen the setscrew which locks the coupling slightly, do it in such a way the coupling can slide over the shaft of the coupling but when rotating the motor schaft will still turn along with the coupling
5. Now when you rotate the coupling by hand, you will notice that the motor will wiggle a little bit. The goal is to reduce the wiggling to a minimum.
6. keep rotating the coupling and try to reposition the z-axis motor including bracket in such a way that the shaft will get more in-line with the z-axis spindle
7. Keep doing this until you think it doesn't get any better. Now carefully fix the setscrew, without forcing it out of line.

Print the following test piece.
test_thinwall_export.gcode
(62.13 KiB) Downloaded 141 times
Part sliced at 0.1mm layer height to better see banding effects
test_thinwall.STL
(11.8 KiB) Downloaded 147 times
Hold it against the light and if you don't see any banding you got it tuned perfectly.

dognotdog
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Post by dognotdog »

I finally managed to do the Z axis tuning as described above, and there's still a bit of wobble left, but just about enough to be observable on the test piece, and I think it won't get better without a proper Acme or ball screw spindle. Mission accomplished, I'd say.

dognotdog
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Post by dognotdog »

Just a set of pre and post tuning prints:
Image

The 2nd figure had different support settings in slic3r, which weren't quite rigid enough for the ears, thus those are quite ugly up until they merge into the head. The figurines are about 5cm tall, for reference.

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gfeliksdal
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Post by gfeliksdal »

The second part significantly looks better, the z-wobble is still a bit present. It could be that your spindle is bent. I had that on one of my printers. I kept tuning in assumption that it could be tuned out. But after removing it from the printer and rolling it over a flat table you could see that it was bent. Replacing it with a straight spindle removed the z-wobble.

dognotdog
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Post by dognotdog »

I did try to roll the spindle on a flat surface, and couldn't see any deviation, but when mounted, I could still see it move about 0.1mm. Could be that the motor coupling isn't perfectly bored, as I managed to tune the motor so far that there's no perceptible wobbling of the motor. I think the wobble is below what's bothering me, for the moment. If I need to do a part where it matters, I might try getting another threaded rod from the home improvement store, though I've also been thinking about replacing the M8 rod with an ACME threaded rod.

danielkschneider
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Post by danielkschneider »

I managed to kill (almost) the spindle-to-motor connector by tightening too much after it got loose at some point.

Bought a metal one since Fastphil told me about it some month ago. It seems to me that the z-axis works better now also in terms of wobbling, but that could be a side-effect from reattaching the spindle.
http://www.cubic-print.com/epages/63251 ... /03_z_coup
Main cost is shipping :)
The new Wellenkupplung
The new Wellenkupplung
Might break soon
Might break soon
PS: That's the nice thing about the Felix. Except for its innovative frame it does use standard pieces :)

dognotdog
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Post by dognotdog »

danielkschneider wrote:I managed to kill (almost) the spindle-to-motor connector by tightening too much after it got loose at some point.

Bought a metal one since Fastphil told me about it some month ago. It seems to me that the z-axis works better now also in terms of wobbling, but that could be a side-effect from reattaching the spindle.
http://www.cubic-print.com/epages/63251 ... /03_z_coup
Main cost is shipping :)
I ordered that coupling, and mounted it today. Boy, what a difference it makes. Even though the spindle looks like it wobbles more, it all happens at the coupling, and there's no more wobble on the printed parts. I'd definitely recommend it, even though it's not a perfect fit, as the set screws tend to grip the spindle's thread unevenly, and make everything a bit lopsided, so one has to fiddle a bit.

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