Anti Z wobble Z nut

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piercet
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Anti Z wobble Z nut

Post by piercet » Fri Jul 31, 2015 6:36 pm

My Taz has a very tiny, but noticible in light, Z wobble. This is a part that attempts to remove that Z wobble by converting the 4 3mm heat set insert mount holes into passthrough bearing surfaces. The theory is that the new part will ride on 4 25mm long nylon M3 standoffs and allow the leadscrew to only influence the up and down motion of the axis. Dunno if it's going to work or be usefull. I'm printing it now, so we'll see!
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cnr0616
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Re: Anti Z wobble Z nut

Post by cnr0616 » Tue Aug 04, 2015 12:05 pm

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Last edited by cnr0616 on Fri Apr 08, 2016 9:37 am, edited 1 time in total.

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piercet
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Re: Anti Z wobble Z nut

Post by piercet » Tue Aug 04, 2015 1:49 pm

Printed fine, haven't got it bolted up yet because I need some additional spacers for the other side. Looks like it should work though. My main concern is the spacers might not provide a good enough glide surface. Some graphite powder should take care of that possibly.

voi9viper
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Re: Anti Z wobble Z nut

Post by voi9viper » Sat Aug 15, 2015 6:47 pm

Have you thought about ball screws for the Z axis. In a 1605 x 300 mm size they are fairly in-expensize, unlike getting 8mm ones, These would be a lot less likely to bend, but I think would need nema 23 motors to drive them. I'm going to try this I think becasue most of my prints either fail entirely, or have obvious missed Z steps. I rarely see an X / Y missed step, but a 47mm print was only 312mm tall :( The problem was reduced by lossening a few screws, but I think you will find that objectionable, too. Bolts / Nuts should be tight, spacers should be used where movement is desired. I'm going to make a new post describing my efforts to get a good Z axis print, which I have band-aided for now with software.

Any thoughts?

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Re: Anti Z wobble Z nut

Post by piercet » Sat Aug 15, 2015 7:20 pm

I've installed ballscrews on an ao- 10x http://www.thingiverse.com/thing:547327 which was the precursor to the taz. They work well. I don't know that they are going to be a major upgrade over the existing leadscrew in this application though. The biggest remaining issue with the taz (which in its own right is a fairly minor issue) is the minor z banding. You can bairly see it on my machine but it is still there, and on my taz at least is almost certainly due to the z bushing to rod gap. I just finished the other anti wobble nut, but it might not be very effective at all until I fix the constraining z rod issue. Parts for that project don't get here until next week though heh. If that project doesn't do the trick belts or a ballscrews will be on the list to try. A nema 17 motor will turn one of the 1605 ballscrews just fine though.

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Re: Anti Z wobble Z nut

Post by voi9viper » Mon Aug 17, 2015 11:46 am

I keep getting missed steps on the Z axis and the only thing left is to increase the torque, or reduce the friction. What length ball screws should i order? 250 mm stroke, 300 mm total length, etc. Until I can work out feedback positioning I may just add the NEMA 23's, since that seems like a simple project.

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piercet
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Re: Anti Z wobble Z nut

Post by piercet » Mon Aug 17, 2015 4:37 pm

The mitsumi leadscrews have an overall length of 420mm. There isn't a whole lot of room to put anything larger than the 12mm wide leadscrew in that particular spot without a major reconfigure. In particular the larger ballscrew nut is going to be hard to fit. Its probably doable if you move the linear rod outward.

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Re: Anti Z wobble Z nut

Post by voi9viper » Wed Aug 19, 2015 1:29 am

I'll let ya know tomorrow. Got in a pair of 84 oz/in NEMA 17s today and so far they miss far less the the 56 oz/in stock steppers. As part of the upgrade I think I want to convert the X carriage to horizontal. It just makes sense to distribute the weight instead of hanging it off the back. Eventually I'll use a very minimal X carriage, probably just holding a Kraken hot end. next is locating some kind of slippery tubing much closer to 3mm then 4mm PTFE, and water cooling the hotend because a bowden setup needs more retract (I refuse to call it suck).

I also got some new 3/8s PEI and manage to need dynamite to blast off a big flat ABS plate extruded at 250 degeees.

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Re: Anti Z wobble Z nut

Post by piercet » Tue Sep 22, 2015 1:08 am

I finally got this bolted on to my machine, and it works great. I used threaded spacers and 8-32 bolts to provide a glide surface off the two side plates. What I discovered is that it reduces the Z wobble to absolutly Zero... in the X direction. It does nothing to address the Y wobble, which is also present. So, i created a second version to test that had Oval shaped slots. That lessens, but not quite eliminates the Y wobble, but I introduce another issue where the nut is actually able to turn on the pins, causing a slight Z layer height error, and enabling the nut to turn in such a way that it binds, restoring the Y wobble. Which is admittedly very small. Springs on the pins might do the trick, but I think thats going to force the X wobble back into place. So, more radical action is required.
wobblenut 3_0.png
With the current configuration, I have a total of 12mm I can potentially play with before the bottom of the nut could potentially impact the Z carriage with the Z adjustment endstop target thingy spring/bolt removed. In reality i can probably go another 5mm beyond that and never have a problem, but I'm trying to keep things as compact as possible. So, what I am toying with if I can make it fit and make it robust enough, is a Y rod slider system made out of 4.75mm hardened steel pins (that you can apperently just buy! I've been making them for years and I hate making pins! i'm really excited about that in case anyone was wondering). There will be one pin in front, and one pin behind the leadscrew, and the leadscrew mount iself will be on the lower section, which will be able to slide back and forth in the Y direction. The X sliding mechanism and pins seems to work quite well, so i am going to largely leave that alone. I'll probably extend the pin socket to improve wear life a little, and the sideplates will change quite a bit to accomodate the lower section.

The weight of the X axis will partially be supported by the Z bearings, and will mainly rest on the Z nut itself. There will be a potential failure point at the edges of the upper nut holder frame where the pins intersect with the sidewalls, which is of concern. I can't go very much wider in that spot due to the other pieces there, especially the Z bearing block. I can probably fit a larger pin in the outer pin hole, but the inner one will actually end up extedning under the side plate itself. I just can't get a bigger pin in there unless I take some of that 5mm space I mentioned above, and even then i'm not sure I can get enough thickness on the glide section for that side. So, thats why I'm posting this unfinished picture. If anyone has any ideas, please let me know. I can go up quite a ways, so 2 outboard pins stacked on top of each other is an option, or potentially a 3 pin setup.

To be continued!

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Re: Anti Z wobble Z nut

Post by piercet » Tue Sep 22, 2015 9:52 am

Looking at this again in the morning, there may be a simpler and stronger way to do this. Instead of pins, I can use M3 screws pointing down riding in channels on top of washers, with spacers to set the depth. That eliminates the risk of a tab breaking, so I'm kind of liking that idea more at the moment if I can fit it in there. Which is kind of a shame because I alreadyy bought 4o pins of different sizes.

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