Improve Z-Axis precision

[Supertramp]

Hi everyone,
I have a Geeetech Prusa I3 X and i noticed that the extruder don't move precisely when i move in Z axis, in fact, when I control Z axis, you can see the nozzle that describes a helical path. I think that will cause (or increase) the tipical "waves" on the vertical surface of the objects.
So I will ask you, if you have any type of idea to improve the precision of Z axis trasmission.
Thanks and happy Easter

[William]

Hi,Maybe the bearings are stuck, you need to check the rods, are they bended? the diameter of the rods, could it be too big for the bearings to move?Besides,you can take a look at this video to improve the Z-Axis precision:http://www.thingiverse.com/thing:1424358.

[atgaskins]

Try this idea: https://www.thingiverse.com/thing:847561
BUT using these top Z-axis rod plates from this collection, without any bearings in them for the same effect:
https://www.thingiverse.com/thing:2143158

Threaded rods are ALWAYS less than perfect. Think about it, you have two much straighter (presumably) smooth rods on either side of the threaded rods, so locking the threaded rods in to place is unnecessary, as it only serves to encode their flaws on to your print. I am wanting to improve on the above design a bit. I don't think they need to be totally flopping about; I think even enlarging the existing holes in the acrylic by a couple hundredths of a mm would be enough. I see a lot of people knocking Geeetech for quality, but just took my time and made my acrylic frame snug, put lock-tight on all frame screws, and it's solid and prints on par with 'other' brands that offer far more expensive entry level pre-built units. My only gripe is the bearings in the belt pulleys are very poop, both my pulleys failed due to that. I replaced them with equivalents from the hobby store (Traxxis TRA7019 is the part from HobbyTown FYI, I'd get some on hand). So far they haven't failed. Sorry to diverge from the topic there... but I hope the link and/or suggestions help with your z-axis issues!

(edited because I initially posted the first link only by mistake, but even though that guys idea is solid, his stl's are quite incorrect dimensionally, you want your smooth rods to be rock solid! so use the tops from the second link!)

[atgaskins]

One other thing... on my unit my X-axis rods were waaaaay too tight, I literally had to hammer them in to the brackets that connect to the Z-axis rods. Oddly, I think this turned out to be a HUGE factor in minimizing my X-axis play, at least the effects of the belt tension pulling the Z-axis bars in ever so slightly. I've seen now that most people can insert and remove their rods with ease. I dread the day I will have to remove mine, but for now I'm considering it a blessing. So my point is just that what might seem like Z-axis noise in your prints could also be somewhat caused by belt tension, especially at high print speeds / high acceleration. To reduce this without ridiculous tight rods that I may never be able to remove without screwing something up, haha... try to pre-tension your collar clamps on the insides of the X-axis. I'd go so far as to say that if you push those out just enough that when the Z rods push back they are very snug then the outer collars are just redundant. Just be careful not to go too far here. But most people just push these these collars to the ends and tighten, but that leaves some play. You need to have a slight tension to prevent the X-axis belt tension from being encoded on the print via it's stress on the Z-rods... does that make sense?