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Z axis artifact

Posted by cat.farmer 
Z axis artifact
December 29, 2013 08:30AM
I am really pleased with my prints, but I have a reocurring band in them. I can't for the life of me figure out why. it shows up in everything I print and on all 4 sides. my only guess is that the z axis is missing a micro step every 5-7 movements up. speed has no effect.

0.35 nozzle
0.28 layer height
PLA @ 190c
Perimeter speed is 20 mm/s
Extrenal perimeter is 60%
open | download - CAM00082.jpg (151.8 KB)
Re: Z axis artifact
December 29, 2013 08:55AM
What are you using for a printer and, more specifically, what are you using for your z-axis lead-screws? Metric or imperial? Threaded rod or something more precise? What diameter/pitch? Assuming that your z-steps/mm are calculated correctly, my first hunch is that 0.28mm is not your optimal layer height. If your layer height requires your z axis to move in fractional steps, you will get this kind of cumulative effect. The Prusa calculator is a great resource, and has a section about determining your optimal layer height. [calculator.josefprusa.cz]

Edited 1 time(s). Last edit at 12/29/2013 09:12AM by stonedcoldskier.
Re: Z axis artifact
December 29, 2013 09:38AM
I designed and built my printer, though it is based off of a mix of Prusai3 and MendelMax2 and a lot of reading. It is still a work in progress. I have attached a picture. All the failed prints hanging from the top, that is what you get when you try to go cheap on a hotend. Best money I spent on the thing was a good hotend.
I am using Imperial threaded rod for the Z, 5/16 - 18.
My #define DEFAULT_AXIS_STEPS_PER_UNIT for the Z is 200.0*16/1.41111. and I do have the mircosteps set on the RAMPS (all 3 jumpers inserted). I did use the [calculator.josefprusa.cz] when I was calibrating.

My thinking is if my Z steps or layer height were bad, wouldn't it slowly drop my Z until I was draging through the print? or am I seeing a "correction" in my z height, where it is pushing out the layer causing the band?

That does bring up another question about layer height and Slic3r, does Slic3r adjust extrution rate base on layer height, so if I were to decrease my layer height, it would adjust my flow rate to compensate? or is that an absolute number based on my setup?

Edited 1 time(s). Last edit at 12/29/2013 09:42AM by cat.farmer.
open | download - CAM00093.jpg (498.3 KB)
Re: Z axis artifact
December 29, 2013 09:59AM
I like how you built your own printer in this free design smiling smiley

Once I had the same issue, it had to do with the stepper drivers overheating, even though they performed quite well they still overheated. Maybe I misread, but do you have a cooling fan on your stepper drivers, and cooling elements on them?

Also, once I had Z-wobble, but it didn't look quite like your Z-errors, so I guess it's probably not Z-wobble.

Oh and btw, nice wallpaper winking smiley

Edited 1 time(s). Last edit at 12/29/2013 09:59AM by Ohmarinus.
Re: Z axis artifact
December 29, 2013 10:25AM
Great repstrap! Your z-steps/mm looks correct, but I still think that you need to change your layer height. Back to the calculator, your layer height of 0.28mm requires 39.688 steps per lift. As explained by Prusa, the axis jumps to the closest full step and introduces error. If you change your layer height to 0.2822, it will take an even 40 steps for every z-lift. There may be other things at play, but this is an easy way to eliminate any error from drift in your z axis. Slicer will automatically compensate for your layer height and extrude the correct volume.
Re: Z axis artifact
December 29, 2013 10:27AM
I do cool my drivers, although right now it is done with the output of the cooling fan from my ATX PS. I am going to print a ramps box w/ fan sometime soon, when I have 6 hours to babysit the printer.
thanks for the kind words on the printer. your goint to laugh, but the frame is my daughters old futon frame, but it worked out perfectly.

I knew someone would comment on the wallpaper.. house is 130 years old, so it is to keep that period feel in the dinning room.
Re: Z axis artifact
December 29, 2013 11:28AM
How tight are your belts on your other axis ?
When my printer starts building non perfectly vertical side walls, I know my belts have worked loose.
I can play mine like guitar strings. (both x and y)

It could be exacerbating some tiny variance on your Z axis. What does your Z anti backlash look like ? are you confident it's working ?

hope you get it sorted,


Re: Z axis artifact
December 29, 2013 04:05PM
Well I've run through all of the sugestions with a little improvement, but not much.
incressing to .2822 height did not make any noticeable change.
I also tried .30 just to see what wuld happen, it created gaps in my sidewalls, but I could still see the bands though not as bad
reduced my extrusion mulipler from 1 to .90 which made things look better, but created gaps also
checked my belts and check tightness of everything, no change.
I guess I will just keep playing with the settings until find that sweet spot.

Thanks everyone for the sugestions
Re: Z axis artifact
December 29, 2013 08:09PM
As Dave S had asked, are you using an anti-backlash mechanism on the z axis? The weight of your x-axis should mostly negate the effect, but it could explain what you are seeing. Also, have you checked the diameter of your filament to make sure it's consistent?
Re: Z axis artifact
December 29, 2013 08:58PM
Im not sure what an anti back lash mechanism is.. so i guess not.. but the z seems stiff enough.. i'll do a little seaching on that. Filamet jas been checked, and is correct in slic3r.
Re: Z axis artifact
December 30, 2013 12:26AM
Compare the defect with the pitch of the threaded rod. If it's the same, it's mechanics of the leadscrew, somewhere.

I had the same issue and I'm not entirely sure that this was the answer, but it's gone now that i've moved to acme leadscrew and completely replaced the drive mechanics of the Z.
Re: Z axis artifact
December 30, 2013 12:45AM
It looks to me like you have a z-wobble. Nothing in your settings can fix a z-wobble. You need to decouple your Z axis lead screw and nut from your gantry and/or decouple your lead screw from your stepper. From looking at your picture the first step I would take would be to replace your solid couplers with some aluminum helical couplers.

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Re: Z axis artifact
December 30, 2013 07:49AM
It never occured to me to compair the banding with the lead screw.. I'll be damned if they don't match..so Z-wobble it is.. Thanks..
now to order more parts.. not sure who hates me more the mailman or my wife..
Re: Z axis artifact
December 30, 2013 08:21AM

you could try this...

if you have a bit of clear plastic pipe around that will fit over your lead screws.
Print yourself a couple of little clamps, take off your couplings, replace with a bit of pipe, and clamp it on your leadscrew and stepper shaft.

Like This : CLICK HERE

Backlash is issues with the play of the nut on your leadscrew. You can "wiggle it up and down" a tiny bit.
This can be prevented by using a spring against the nut to hold it at one end of it's travel.

Like this.. (the thread is then screwed through the nut and spring).

Anti Backlash

or.. why not print a helical coupler from thingiverse ? Plenty around!
(Whats the point in using the postman/cash, when you have a 3D printer!)

Hope this helps.

Edited 1 time(s). Last edit at 12/30/2013 08:23AM by DaveS.
Re: Z axis artifact
December 30, 2013 09:24AM
After I posted and sat back with my coffee.. It occured to me I could get one from thingiverse.. DUH!

As I have to design and print new X carrage peices (ok I don't have to, but why not) I will see if I can incorperate an anti backlash setup into them.

Thanks again everyone.
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