Unexpected spiral groove on the object surface

As you can see in the picture I printed this with Hbot printer, there is a spiral line on the object surface. Below are my analysis:
a. Extrusion issue: this looks like my extruder periodically overextrusion or underextrusion. Maybe the step motor lost step sometime.
So I try to raise printing temperature from 190 to 220C(PLA). Turns out the surface is more smooth and shinier at higher temperature but still have the spiral groove.
And i also enlarge the extruder voltage, then i got no improvement but annoying sound from the step motor. Anyway the extruder motor is doing well
b. Slicer issue: I’m using cura for this printing, maybe i should try other slicer ?
c. Belt assembling issue: belt is too loose to maintain a good repeated positioning accuracy?

Do guys met problem like this one? Do u have clues how to fix it?

Any ideas are welcome! Thank u very much ;-)

... have you measured, if the spiral metrics are "harmonics" of the Z-axis thread?

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Was that print sliced in regular mode or in spiral vase mode?

Edited 1 time(s). Last edit at 01/25/2021 02:00AM by dc42.

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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].

@VDX
Hi VDX! Thanks for giving attention!
I’m not quite sure what “harmonics” means in this situation. The “thread pitch” on the object surface is not constant. It’s smaller in thick part (bottom) and bigger in thin part(top).
Do u think the Z-aix thread is frayed and bed is moving on the XY direction?

@dc42
Hello dc42!
It’s sliced in regular mode!

In the photos I see areas that look bulged and areas that don't. In the bulged areas, it it bulging all the way around the print at the exact same Z level, or does the bulge act more like screw threads as it goes around the print?
If it is bulging on the same Z level, that would suggest that the Z axis is not stepping evenly and there is a repetitive error. On the layers where the step size is smaller than it should be the plastic will bulge all the way around the perimeter of the print.
If the bulge is more like a screw thread that spirals up the print that would suggest a problem with the XY motion.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

... if steppers are not "strong enough", they'll act like springs, so the step-length is only exact at the fullstep-position and will be "gradually compressed" between the full steps, what could cause such effects ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Hi @the_digital_dentist!
I’m excited to hear about the bulging theory!! In this “horn” print it is spiral up like screw thread.
But I also meet the situation which is relevant to what you described about Z-aix not stepping evenly. there are bugling which is totally horizon on the print surface(pls have a look on picture attached).
I wondered if there is any way that i can test and calibrate the Z-aix stepping performance? Just like how to test the hanging angle or else
Thank u very much & have a nice day!! :-)

It looks like it may be tied to your Z_Axis threaded rod/lead screw. If you manually raise and lower the Z_Axis, can you see the nozzle tip describing a circle as it travels up and down the rod/screw? I'm assuming a single Z_Axis screw drive rather than a twin screw which I don't think would give a perfect spiral as the screws would interact with each other in some way.

My two cents.

Play Bonny!

Hi @VDX !!
I have been thinking and doing research about step motor these days.
Do you mean that if the step motor is not “strong” enough, maintaining the bed on a specific level is difficult?
For example when printing the Z=3mm layer, the bed can probably bounce to Z=2.95 and then bounce back to Z=3.0 or even go down to Z=2.9
And it cause part of the cycle track is “squeezed” out of the planed position, then it create this “spring” on the surface?
Thank u again for sharing knowledge. Have a nice day!! ;-)

Hi @Soadyheid !!
You are right the printer is single Z-aix screw drive. I can’t tell if it’s describing a circle, it’s too difficult to observe!
To test if it’s the problem of Z-aix screw, i reverse the 3D in Cura by upside down, then i got the same print, which means the spring pattern is also reversed following the 3D direction.
So i can tell the spring is not tied to Z-aix screw thread.
Thank u very much ! ;-)

That sounds like an XY motion problem. What sort of mechanism does the printer use? Photos?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Hi @the_digital_ dentist!
Attached some pictures for your.
Thank u very much!