Z Axis Ribbing Issues

While Tessaract works to gather data about how & when this issue started so we can nail down possible changes/causes, I thought I'd start a thread specific to exactly how this issue is affecting prints.



Can someone else who is having the banding/ribbing issue print a 15mm calibration cube and measure the height of the completed object?

If it's like mine it will come out to 14mm tall with 10 ridges (1 every 1.5mm, including the bottom layer as a ridge.)

My cube was printed at .1 layer height (.1058 also to the same effect).

 

Replace the threaded rods and nuts in the Z-axis This is probably the contortion of these bars during transport.

 

Jack, some people have still seen this ribbing when using M8 rods and nuts.

Do you think they're getting bent in shipment?

 

Yes, I change it and look for effects

 

You changed to M8 or just different 5/16"?

Those look great. I'm assuming it's 3 parts. Does your printer have the auto-level upgrade?

 

Just saw some info on Z wobble issue on other forums. I haven't tested it yet.

http://forums.reprap.org/read.php?1,130622,130693


http://www.thingiverse.com/thing:9326

or

http://www.thingiverse.com/thing:9622

According to the comments on Thingiverse.com, people seemed to confirm these sovled the z wobble issue.

My guess is those people who swapped the metric rod were able to better align the stepper motor shaft and the threaded rod, thus improving their print quality.

Again, the above is only my guess as I haven't tested them out yet.

 

This is M8 but if you see (picture) thread on this bars is diffrent. Orginal is in inch, but mine is metric. I thing that is the problem. Software is metric but bars have therad in inch. On picture left is mine, and on right i orginal. I don't have autolevel upgrade. In Poland i can't buy this upgrade

 

I have my own stabilization patent

 

I upgraded mine to metric as well. Though I never got ribbing NEARLY as bad as this. Now that I'm on metric I don't see any.

The working theory is due to step count.

Right now the printer uses 5/16-18 threaded rods. Using This Calculator you can see that for a .1mm layer height the step count is: 14.17434443656981. The stepper driver receives 2 signals, speed and step count. I believe it only takes integers and not floating point, so that value above is truncated to 14steps. Even though the counter keeping track of position won't truncate that informatoin.

This means on layer 1 it moves up 0.09878mm. The next layer it thinks that it will have traveled 28.34868887313962 steps. Though in reality it's only done 28 steps and is at 0.19756mm height. This leaves .00244mm difference in material.

This material difference accumulates for 6 layers until the step count reaches 85.04606661941886. It will add in the extra step at this point. Now the step count is more back to normal and will continue it's cycle.

The excess plastic during the rounding steps will cause it to form ribs as seen. When it works back to normal it won't have the excess, because of the extra step.

At least that's what the current guess is.

According to the math using a layer height of 0.09878 instead of 0.1mm should remove the ribbing. Unfortunately this hasn't been the case in all instances.

 

Mike, thanks for the detail explanation. I'm learning something new.

As you mentioned above that people changing to metric rod can not completely get rid of the ribbing issue.

Maybe these two different issues would have print quality effects?

Maybe metric rod would eliminate the inconsistent height layer issue due to the round off, and better alignment of the stepper motor shaft and the threaded rod reduces the alignment error?

 

Cvcp


Sent from my iPhone using Tapatalk

 

I noticed that Cura does account for the error to some degree. During printing, it adjusts the layer height from 0.9mm, 0.19mm, then 0.30mm, etc....

So my guess is that metric rod would keep the layer height more consistent. Using non-metric rod, if the slicer software is aware of the non metric rod through the firmware setting, each layer thickness would vary a bit so there shouldn't be any excess plastic to be squeezed out to the side.

As for the ribbing to the sides, my guess would be that it is due to the misalignment of the stepper motor shaft and the threaded rod.

There's an interesting article talking about wobble issue.

http://www.designworldonline.com/5-...-printing-and-subtractive-machining-design/#_

Again, all of the above are just my wild guesses.

 

@ Ziggy, thank you for your explanations. I'm learning more about the difference between Z ribbing and Z wobble.

 

So... I have not upgraded my rods to metric, have not removed & realigned them and have not adjusted belt tension.

And my ribbing/wobbling issue appears to be gone.




The only things I've done to eliminate it has been to add Z-Stabilizers on the straight rods for Z and print at different temps.

Printing the Blue Calibration filament at 195 = ribbing. Printing at either 175 (slight de-lamination) or 215 = no ribbing.

I've used the calculator for correct steps ever since my 2nd or 3rd print and still had the ribbing.

 

I'll print the z stabilizers tomorrow do you have the link to them. I'll. Post my results once i've tried out your suggestions. Thanks

 

http://www.thingiverse.com/thing:278484

Those are the stabilizers I used.

I would start with just those. The temperature thing is going to depend on your individual conditions for your location and the filament you're using.