Anyone know about textured patterns around perimeter?

Hi everyone,

Here's some info about my setup:
Reprap
Arduino/ramps
Marlin (Folger Tech version)

I'm new to this site, though I'm not as new to 3D printing. One problem that seems to keep eluding me is this strange texture I get on the outside of my objects. I can't seem to find anyone else who has had/solved this issue. I'm not really sure how to describe it. It has a texture reminiscent of snake skin. Normally, I wouldn't be concerned, because I generally get nice prints, however I am able to feel small, patterned "bumps" when I run my finger along the edges, so I am sure it affects the dimensionality of my models to some degree. I would just love to get smooth, organized lines around my perimeters. If I can fix this, my prints would be perfect.

Here is an image so you all can see for yourselves:


Thanks for the help, I appreciate it.

--Nick

Edited 1 time(s). Last edit at 10/25/2015 08:30PM by NickPeak53.

Quote
NickPeak53
Hi everyone,

Here's some info about my setup:
Reprap
Arduino/ramps
Marlin (Folger Tech version)

I'm new to this site, though I'm not as new to 3D printing. One problem that seems to keep eluding me is this strange texture I get on the outside of my objects. I can't seem to find anyone else who has had/solved this issue. I'm not really sure how to describe it. It has a texture reminiscent of snake skin. Normally, I wouldn't be concerned, because I generally get nice prints, however I am able to feel small, patterned "bumps" when I run my finger along the edges, so I am sure it affects the dimensionality of my models to some degree. I would just love to get smooth, organized lines around my perimeters. If I can fix this, my prints would be perfect.

Here is an image so you all can see for yourselves: [attachment 64647 20151024_211509-1.jpg]

Thanks for the help, I appreciate it.

--Nick

I believe such imperfections are caused by vibrations in the machine as it print. I would suggest going around your printer and making sure that all of the nuts and screws are tight, and that there are no conditions that would allow for excessive vibrations in the bed or the hotend/print head. Also, you could try putting dampeners under your printer if you have it on a very hard sturdy surface, to eliminate any possible reverb from the printer to the surface and then back to the printer.

This is a regular pattern with equal spacing in each layer. That means something slow and periodic is happening. Try cleaning filament dust off the filament drive gear in the extruder- if it has dust from having chewed the filament, the dusty areas won't bite as hard and the filament won't extrude properly until the gear turns to a cleaner area of its teeth. Watch the drive gear rotate and see if it is cenetered right on the motor shaft. If it isn't, you found the problem.

Edited 1 time(s). Last edit at 10/24/2015 10:49PM by the_digital_dentist.

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

Do you have linear bearings with a flat spot or just plain cheap quality?
-Olaf

Mach,
I have gone around my machine and checked all of my connections, everything was tight, so I tightened them some more. I don't think it had much effect on my following print. Also, my machine has rubber feet, so I'm not sure if vibration would be an issue or not. What else could I try for vibration dampening?


the_digital_dentist,
I took apart my extruder and cleaned the gear and the rest of the casing. There was a bit of dust, but not much at all. The drive gear rotates on the shaft of the stepper perfectly. It didn't seem to make a noticeable difference in my following print.

Olaf,
They are the fully enclosed, cylindrical bearings. Yes, they are the "cheap" ones, but all my axis slide smoothly, with no grind whatsoever.


Attached is a photo of the same part printed after your suggestions. I decreased the layer height from 3.5mm to 2.5mm. This did seem to minimize the effect, but as you can see, it is still present. I have a feeling this is caused by pixelation in the steppers. Would it be possible for the layer height to accentuate the steps taken by each motor? (In other words, could this be caused by each step "snapping" into position rather than flowing through its steps smoothly?) If so, is there a way to adjust this in the Marlin firmware? I can upload my configuration.h file if anyone would like to check it out, just let me know.

If it helps, I have an MK8 direct drive extruder with a 0.4mm nozzle.


Here is my attempt made at the same part after those adjustments:

If you all need any files or photos of my machine, let me know. Feel free to PM me
Thanks everyone for your suggestions,

--Nick

Get a ruler to check how long for each wave. May be it is because of timing belt teeth.

It's happening along both the X and Y axes in every layer, so it is either an extruder problem, an X and Y motion problem, or a slicer problem. Can you see the same pattern in the infill?

Try a different slicer. If it does the same thing, then you know the problem is in the machine.

Check belt tensions in X and Y. Check that the pulleys are centered on the motor shafts. Take the belts off and try sliding the extruder carriage and the bed back and forth- they should move easily and smoothly.

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

Wouldn't this be due to the settings i.e. rectilinear fill pattern, and 10% fill which would crisscross lines on layers?

My guess is that it is an extruder problem. I was going to suggest you check whether your hobbed bolt is eccentric, but I think that would give a very long repeat interval in the pattern - and although you have not given us any idea of the scale of your photos, I suspect that the pattern repeat interval in your photos is much smaller than you would get from an eccentric hobbed bolt.

Some questions for you:

1. What is the repeat interval of the pattern in your photos?
2. Are you using x16 microstepping for the extruder, or a lower value?
3. What extruder steps/mm do you have set?
4. What extrusion width and layer height did you use for that print?
5. If you increase the extrusion width or the layer height, does the pattern repeat interval change?

Edited 2 time(s). Last edit at 10/29/2015 01:34PM 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].

Print it at 20mm/sec and see what happens.

Edited 1 time(s). Last edit at 10/31/2015 06:22PM by elwood127.

Hi guys,

To me, according to the regularity of the pattern, it's a mecanical issue.
I had the same kind of pattern (much lighter) because of mooth idler pulleys.
I replaced them by proper GT2 pulleys and the pattern desappear.

++JM

Check if the infill also has a pattern in sync with the perimeter, in that case it could be the z moves up and down in a sine wave pattern, could be the heated bed poorly driven by bang-bang control or the extruder not running smoothly but at the same pulsed rhythm. This can be caused by the step stick in the wrong decay mode. It sort of jumps from full step to full step in jerks instead of smoothly microstepping.
Long story short on A4988 sticks R4 is usually 10K, but can be shorted so that the stick runs in low current mode. This is usually the case as extruders run very slowly. When the step stick is in mixed mode it runs much smoother once the correct current is set with the potmeter. The 8825 has a similar mode. Search for stepstuck for more info.

Quote
J-Max
Hi guys,

To me, according to the regularity of the pattern, it's a mecanical issue.
I had the same kind of pattern (much lighter) because of mooth idler pulleys.
I replaced them by proper GT2 pulleys and the pattern desappear.

++JM

I once had a similar problem and tried twisting the belts so that the smooth side of the belt was against the smooth pulley. It didn't change anything.
Now I use a smooth pulley in my X axis without the belt twist and can see no pattern in the prints whatsoever. I don't think the pulleys are the problem here.

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

Hi,

I understand the problem was different on your machine.
On mine, it was a great print quality improvement, no possible doubt.
To twist the belts can be a way to figure out if it's the problem here.
I keep that trick in mind.

++JM

Try tweaking the extruder motor current and see if it affects the waviness.

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

That sure looks like Z Wobble.

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My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
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