Z banding in all prints

I have been having a discussion on another forum and part of it was the Z banding I am getting on all prints. This problem was not so pronounced over a year ago but now it is spoiling the look of my prints.
My Y and X belts are tight and the Z gears have a little backlash in them but I don't think that is the problem.

It looks to me as if as the layers are built up there is a slight shift in the Y and X position of a fraction of a mm and over the next 3 or 4 layers it is corrected, only to start again. This pattern is repeated throughout the height of the object.. I hope the following photos will show the problem clearly enough.




any thoughts? Could it be to do with the direction the plastic is laid down? The correct XY position when traveling left to right should be the same position when traveling right to left but is there something in the firmware or slicing software that would position the object slightly wrong?
I have tried lots of different settings to try and get rid of this, different layer heights, extrusion factors retraction, non retraction etc.

Thanks for any help

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

What is the pitch of the banding in the cube print, and what layer height did you use?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
What is the pitch of the banding in the cube print, and what layer height did you use?

It appears to be every third layer with the odd fourth layer, it is really hard to see with just a hand magnifying glass and my poor eye sight. The layer height was 2.4 mm
An earlier test print with the holes and curves was at a layer height of 2.0 mm and the banding pitch seems to be the same , every third or fourth layer.

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

Quote
appjaws1

Quote
dc42
What is the pitch of the banding in the cube print, and what layer height did you use?

It appears to be every third layer with the odd fourth layer, it is really hard to see with just a hand magnifying glass and my poor eye sight. The layer height was 2.4 mm
An earlier test print with the holes and curves was at a layer height of 2.0 mm and the banding pitch seems to be the same , every third or fourth layer.

I presume you really mean 0.24mm and 0.2mm? In which case the banding pitch is about 0.8mm, the same as the Z threaded rod pitch. Try holding the cube against the threaded rod to check. Could be a problem with the Z gears, or the threaded rod may not be straight.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

If the banding is every 0.8mm it is almost certainly an issue with the threaded rod.

1) Make sure the threaded rod is free to rotate off-centre at the top. Forcing the top of the rod to stay in one place is likely to put sideways forces on the X-arm every revolution and cause banding.
2) Check the bottom of the rod is secure in the Z gear and not too much off-centre.
3) Check/lubricate the teeth of the Z gears - rotate the Z screw by hand to check for places it might be sticking.

Also measure the height of a completed print. If the print is shorter than it should be it indicates that the Z screw or motor is slipping (probably at the same place every revolution).

Dave

WELL DONE.
I have printed the Z runner at 0.2mm layer height. That and the cube when held against the threaded rod does fit in with the banding.
So next job is to remove the Z gears, rod and nut and check the play.
I'll post the results tomorrow.
Thanks to dc42 and dmould for all the help.

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1

An update
I found the following problems:-
Z lower mount is split
Z runner is cracked
one Z bearing clamp has one screw hole completely broken off
the Z nut trap is cracked
my long brass nut has play in it

I fitted a new Z runner and the new parts I am now printing apper to be OK with no Z banding.

This has been a good lesson, My printer is printing most days and I suppose I should expect some fatigue after nearly 2 years of work.

Note to self....CHECK THE MACHINE AT REGULAR INTERVALS....

Thank you all for the help and advice.

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appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1