Z wobble hack - printed part

I narrowed down the majority of my z wobble to the double nut on the z lift part transferring the threaded rod wobble into the bed. I thought if the bed tensioning nut could float freely then the threaded rod will not push the table around anymore.

I started off by just removing the nut but that seemed a bit dodgy as WWFP pointed out the spring is there to take up backlash. So I have designed a simple little part that you can add "try" as guinipig if you are getting bad z wobble in your prints.



You can see pictures of the assembled part and get the STL here - The stl prints fine this way up without support.
Pictures

If it’s a bunch of crap or good then let me know. I starting running it today and it seems to work really well. It lets the top nut float around.

FYI you need a longer spring if you do this. Also you need to squeeze it all up when you screw the threaded rod through. You also need to rotate the z home switch back a little but there is plenty of room.

Cheers
Robonz

Edited 1 time(s). Last edit at 01/05/2014 12:30AM by Robonz.

I designed a similar mod for my MG Prusa, but on the nut that does the lifting. It helped immensely. My layer alignment errors are now dominated by the wobbly Mendel frame. Parts for an Ingentis derivative are now accumulating...

Looks like it works well. When you originally built the machine the default way did you make sure the Z-lift bracket was able to move in the Z-arms? This movement was supposed to allow the bracket to absorb the movement in Z and X. It could not deal with the rotation on Y or X that your part relieved. If anyone else tries it and finds it solves the issue I will try and revise the Z-lift to allow for independent movement of each nut in X and Y.

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Hi Sublime

Yes, I even pulled the z lift apart and gave it a very light sanding to make sure it was a "smooth fit". I can now confirm this new part gives me an 80 to 90 % visual reduction in banding and z wobble issues. I also went back to the original coupler you designed as I think the silicone hose could twist a little. I did get my best print ever last night and should post a photo.

I think the part could be tweaked a bit. Functionally it works great but it does make a "click clack" noise on z lifts. Removing that noise would be good. Maybe a printed leaf spring as a part of the part would do it.

Here is a side by side comparison of a challenging print that is 100mm tall. You can see the banding on the back of head is pretty much gone.
.


All I need now is to fix the ooze during a z lift (which is needed on this print due to curling) and I would think the machine is just as good or better than a comerical machine.

On another note I made this thumb nut for quick access to the head for easy regular cleaning. I can put the STL up if anyone wants it. It has an M3 standoff pressed inside.



Cheers
Robonz

Interesting stuff. I'm wondering now about just ditching the threaded rod and going with a cable driven Z. I hate the idea of loosing resolution in Z though.. Anyone consider gearing the cable Z down with some belt driven gears?

Robonz, can Is that some kind of cable tensioner inside your XY end? Something like that is top on my list of upgrades.

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wingnut
Interesting stuff. I'm wondering now about just ditching the threaded rod and going with a cable driven Z. I hate the idea of loosing resolution in Z though.. Anyone consider gearing the cable Z down with some belt driven gears?

Robonz, can Is that some kind of cable tensioner inside your XY end? Something like that is top on my list of upgrades.

Ingentis has a geared belt Z axis similar to Tantillus and works well so I would say yes you could gear down the cable Z.

I believe what you are seeing on Robonz X/Y end is a magnet he is using to hold the loose end of the cables.

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Robonz
Here is a side by side comparison of a challenging print that is 100mm tall. You can see the banding on the back of head is pretty much gone.
.

z_lift_nut_compare.jpg

I forgot to say that is an amazing improvement from a single part being replaced.

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Sublime is spot on as usual. I have some magnets to hold the loose threads from hanging into the mechanism.

If I went to cable drive I would consider using one belt stage of reduction to offer a low backlach higher resolutionn solution. Say 4 or 5 to 1. This hopefully would stop the table dropping too. I would also prefer a belt to a string for the lift as servicing is less fidely.

Talking about belts and pulleys, anyone tried replacing the gears in the extruder with a belt stage? I still have some more pulleys and belts lying around.

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Robonz
I would also prefer a belt to a string for the lift as servicing is less fidely.

The cable Z has a tensioner that makes it much easier and it does not have a hole to thread the cable through.

Also ingentis's gearing does not stop its heavy bed form dropping but I could see it stopping and unheated Tantillus size bed. I actually like that it falls when the print is done. The end gcode returns X and Y to home and then there's an M84 to turn off the motors so it drops right away so the part can not be near the hot hotend.

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Robonz
Talking about belts and pulleys, anyone tried replacing the gears in the extruder with a belt stage? I still have some more pulleys and belts lying around.

The Tantillus repo has printable GT2 pulleys along with the appropriate belt part number. Others have also used generic pulleys and belts of different specs.

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Robonz
Talking about belts and pulleys, anyone tried replacing the gears in the extruder with a belt stage? I still have some more pulleys and belts lying around.

I'm actually working on that now. I considered modifying the original extruder for belt drive but decided on something completely different. I'm attempting something similar to what the ultimaker uses with the stepper motor and extruder mounted up high behind the machine. This will have the added benefit of a considerably shorter bowden tube. I have the extruder body printed. Now I'm working on printing some GT2 pulleys. I already printed a set but darned if I can't find a local source for the M3 keeper nut that the pulley was designed for. I will print a new set of pulleys and hob the new bolt tonight.

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wingnut

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Robonz
Talking about belts and pulleys, anyone tried replacing the gears in the extruder with a belt stage? I still have some more pulleys and belts lying around.

I'm actually working on that now. I considered modifying the original extruder for belt drive but decided on something completely different. I'm attempting something similar to what the ultimaker uses with the stepper motor and extruder mounted up high behind the machine. This will have the added benefit of a considerably shorter bowden tube. I have the extruder body printed. Now I'm working on printing some GT2 pulleys. I already printed a set but darned if I can't find a local source for the M3 keeper nut that the pulley was designed for. I will print a new set of pulleys and hob the new bolt tonight.

I would be careful moving the extruder like that. I believe one thing that makes Tantillus's retraction actually work where Ultimaker failed (at least the original) was the shape of the Bowden tube. On Tantillus the tube forms a smooth curve where as on the original Ultimaker the tube was more of a half peanut shape. This half peanut shape causes the filament to switch sides of the tube each time the curve changes direction which would add hysteresis to the system and negate the shorter tube. It also forces a much tighter turn radius especially when the carriage is in the same corner as the extruder. Also Tantillus's Bowden cable is actually the same length or shorter than the original Ultimakers.

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Thanks Sublime. I'll keep an eye on the shape of the bowden tube with the head at all the extreme positions when I choose a location for the extruder. If I have to, I can also play with the angle that the tube exits the extruder.