Is flexible coupler helpful?

I have been annoyed by z- wobble that happens on my Prusa Mendel. I plan to get two aluminium flexible coupler. Are they any good? I need some suggestion. I tried that z constraInts but they are not helpful.

Thanks.

Edited 1 time(s). Last edit at 02/02/2014 09:02PM by jpan.

I run a Mendel. The aluminum couplers are usually 5mm motor shaft to 8mm threaded rod. If you are running 5/16" threaded rod there will be a center-line offset between the motor shaft and the threaded rods. I run printed solid Z couplers, and I have about 2mm thick rubber washers under my Z motors, not overly tightened screws, so the motor can tilt a little on the washers and absorb any wobble in the assembly. The other end of my threaded rods are free running, using bearing restainers on the rods actually makes wobble worse. This eliminated all my Z-wobble issues.

Edited 1 time(s). Last edit at 02/02/2014 09:45PM by Dirty Steve.

I use tubes, but the threaded rods are near-perfectly straight and both on the tubed machine and the aluminum coupler machine there is no sign of Z-wobble so I guess it's mostly the user that decides how good the quality comes out considering Z-wobble.

The real root of the problem for all of these machines is that the Z is not strong enough the rods should be continually supported and they should be mounted to a stiff frame. The idea is whatever the screw does it should not push the Z back and forth in other words the linear axis should be stronger than the screw

So what I should do now instead of buying a aluminum coupler is to tighten all the nuts and screws on my machine that could affect z linear rod and try again, correct? I tried tube+ plastic coupler this morning and it was no good.
Also, should I tighten the bearing on the linear rod even more? Sounds like that's what I should do...

Edited 1 time(s). Last edit at 02/03/2014 07:27PM by jpan.

Don't walk, run to go get aluminum couplers. I will not go back after using them

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Dirty Steve
...The aluminum couplers are usually 5mm motor shaft to 8mm threaded rod. ....

There are several different configurations of these aluminum couplers to be had - make sure you get the right one for your setup. The stepper shafts are usually 5mm. I originally had 8mm threaded rod on my printer, and had corresponding 5mm-8mm couplers. Later when I went to an imperial lead screw (1/4 inch) I swapped my coupler for a 1/4 inch-5mm. So there are other configurations - if you go this route, just make sure you pay attention.

Most people here do not feel these are beneficial. Certainly, they're not ideal if your motors are above your shafts - too much weight on the spirals. I still have them on my printer, but I think I got better results from 1) removing any Z axis constraints - especially those on top, and 2) decoupling my X ends from the shafts. The nuts are not embedded in the X ends anymore - they are embedded in a separate smaller piece beneath the x ends. I have attached an openscad file that you can customize if you want.

Thanks a lot. I got a lot of suggestions from the forum and I'll try them one by one.

Edited 1 time(s). Last edit at 02/04/2014 01:42PM by jpan.

Check this out: [www.thingiverse.com]

For me, making the change to M6 lead screws solved all of my z-wobble and banding issues. The wobble itself, as CNC_Dick pointed out, is the result of the Z-axis not being as rigid as it should be and the thinner lead screws will flex, allowing the 8mm smooth rods to do their job. Additionally, the change to metric threaded rods with 1mm (M6) or 0.8mm (M5) pitch, along with correct layer heights, will remove any banding issues associated with Z moves which are less than one full step.

There are other posts that will explain things much better than I have, but the comments / discussion on Thingiverse illustrate things pretty well.

Thanks for reply! but now I do't think it's a problem with z-axis
check this post to see my prints please..

Edited 1 time(s). Last edit at 02/04/2014 07:31PM by jpan.

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stonedcoldskier
Check this out: [www.thingiverse.com]

For me, making the change to M6 lead screws solved all of my z-wobble and banding issues. The wobble itself, as CNC_Dick pointed out, is the result of the Z-axis not being as rigid as it should be and the thinner lead screws will flex, allowing the 8mm smooth rods to do their job. Additionally, the change to metric threaded rods with 1mm (M6) or 0.8mm (M5) pitch, along with correct layer heights, will remove any banding issues associated with Z moves which are less than one full step.

There are other posts that will explain things much better than I have, but the comments / discussion on Thingiverse illustrate things pretty well.

thank you somebody finally understands the real root of the problem if somebody is building a machine from scratch and uses stronger Z guides supported it would be nice to see. This is part of the frame and doesn't move I would suggest possibly 16mm supported all the way or real linear rail and bearings. The only extra weight would be the bearings the hard part would be lining everything up there would be no forgiveness because nothing is going to spring so would take somebody with some skill to assemble. Shafts would have to be perfectly parallel if somebody had something that was the right size and used as a gauge to make sure they were exactly parallel top to bottom could be done. jpan has put up a couple more posts and he says it's not happening in the in the right direction so I don't know what would be causing his problem

Edited 5 time(s). Last edit at 02/04/2014 08:24PM by cnc dick.

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cnc dick
The real root of the problem for all of these machines is that the Z is not strong enough the rods should be continually supported and they should be mounted to a stiff frame. The idea is whatever the screw does it should not push the Z back and forth in other words the linear axis should be stronger than the screw

I think going to M5 threaded rods instead of M8 rods would reduce z wobble a lot. This is what was done on the Prusa3. This is a simple upgrade describe in thingiverse.

I use these, Clicky. they allow the nut to wander horizontally while keeping verticle constraints. Great for taking out the last bit of wobble.

So, the nut trap is large and allows the nut to wander? So, this trades some lag in the z nuts to eliminate wobble? I think the Prusa2 x-ends may have been intentionally made to have oversized nut traps to do the same thing. That's how my Prusa2 works.

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brnrd
So, the nut trap is large and allows the nut to wander? So, this trades some lag in the z nuts to eliminate wobble? I think the Prusa2 x-ends may have been intentionally made to have oversized nut traps to do the same thing. That's how my Prusa2 works.

lag? No I don't think so. Up and down the clearance is null, side to side there is play however.