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Blobbing and roughness on vertical surfaces.

Posted by Nas 
Blobbing and roughness on vertical surfaces.
September 22, 2013 11:04AM
I've had a look through all the Z-Axis related issues I can find reference too and have been troubleshooting my printer for weeks but seem to be coming up short. To go through what I've diagnosed and what I've done to try to solve it;

Z-Wobble: removed the constraints on the threaded bolts and printed out a set of these [www.thingiverse.com]
- No improvement.

Microstepping error: used layer heights that are multiples of full steps
- No improvement

Lower temperature and fiddle with feed rate
- Moderate successes and failures, never eliminated the problem entirely.

Fiddle with extrusion width
- Seems to have an effect but I just can't be sure. My nozzle has a diameter of 0.35mm and I find I get slightly better results with this set to 0.5mm in Kisslicer.

I print at a layer height of 0.15mm, extrusion width set between 0.36-0.6

Filament diameter varies between 1.71 and 1.73 (set to 1.72 in slicing software)
Nozzle temperature: 217C

An image of the 'issue' is attached.

Tonight I'll be removing the bridges under the polulu so that my z-axis will only operate at full steps and seeing how that goes. If anyone has any ideas as to what it might be or anything I might try to fix this I'd appreciate it.

open | download - 036mm015h217C.jpg (235.5 KB)
Re: Blobbing and roughness on vertical surfaces.
September 23, 2013 02:49PM
It might be there is water in the filament? That can cause blobbing as the water boils. I wouldn't bother trying full steps, I doubt it is the issue. The blobbing isn't layer-by-layer it's weird, so it might also be the hobbed bolt is a little slippy?
Re: Blobbing and roughness on vertical surfaces.
September 24, 2013 12:07PM
I would suggest trying these settings:

ABS Noz Temp to 230, bed temp to 100.
PLA Noz Temp to 185, bed temp to 60.

A layer height that is some were close to 0.35 * 0.8. (Needs to be an increment of the distance the Z axis lifts your x carriage in one micro step.)
A layer width of 0.4. (Keep in mind this isn't width over thickness. WOT is a number to multiply your layer height by to get the layer width. i.e. layer height of 0.28 with a WOT of 1.43 will give you a layer width of 0.4004)
Speeds to the default for your slicer.
Re: Blobbing and roughness on vertical surfaces.
September 24, 2013 02:24PM
I had prints appearing exactly like that when I first started 3D printing. The problem was simply too much flowto feed rate ratio for the infill. I had been using the same ratio for perimeters and infill regardless of layer height. I found that down to 0.25mm layer height it was sort of OK but for thinner layers I had to reduce the infill flow to feed ratio compared to the perimeters.

Probably you can get the same result by varying (increasing) the extrusion width for the infill, but not for the perimeters.

I think what was happening was that the infill was pushing out against the perimeters, making them uneven.
Re: Blobbing and roughness on vertical surfaces.
September 24, 2013 10:08PM
Water in filament: When I began using the filament there were at times some popping sounds and a little smoke, since I've added a piece of sponge to clean the filament before it enters the extruder this has stopped so there's no indication there's any moisture that's worked its way in.

Slippy bolt: It's possible, I have two bolts separated by a spring for the threaded z rods/x-carriage.

Temperature: I currently print my ABS at 218C. I've found it through trial and error to be close to optimal. Any lower and it struggles, any higher and I get too much ooze. Layer adhesion does not appear to have suffered. It could just be that my temperature readings are inaccurate and so what I see reported as 218 is actually higher. Thermistor reads correct temp at room temperature though.

Layer height: I've removed microstepping altogether from my Z-axis and have all movements in multiples of 6.25 microns (one full step).

Layer width: Tried between 0.36 and 0.66mm with little difference in print quality. I usually keep it at 0.38mm. I get less blobbing with increased width but the misalignment of layers appears worse. It's definitely not z-wobble either as if the surface protrudes from one side, this continues all the way around (there is no inset surface on the opposite side).

Flow/Feed rate: I think it's part of the problem, I've lowered the extrusion multiplier from 0.99 to 0.98 and it improved the blobbing but there seems to be something causing the layers not to align perfectly. With the print shown, there is no infill in the zoomed in portion, it is hollow. I have the infill extrusion width set between 0.5 and 0.6mm (vs. 0.38 for perimeters).

Thanks for the feedback. Over the next couple of days I'll try fiddling some more with extrusion width and the feed rate.

I'll also go back to thicker layers around 0.25mm and see how that goes.

I've been looking at WOT, though I don't think Kisslicer has any setting regarding this parameter? I'd go back to slicer but it's unbearably slow at the moment.

I stumbled across a thread mentioning the diameter of free air extrusion and noticed that mine more closely represents the results from a 0.5mm nozzle. While I'm sure mine was labeled 0.35mm, I'll muck around with the extrusion width settings again and see how it goes.


Re: Blobbing and roughness on vertical surfaces.
September 27, 2013 11:03PM
Ok just to update, I have managed to eliminate the blobbing.

To summarise the changes I've made:
Increase temperature a few degrees (217 -> 220 degrees)
Increase extrusion width (0.36 -> 0.45)
Increase layer height (0.1 -> 0.15)
Fiddle with E-Steps per mm.
Increase retraction by 0.05mm without increasing prime value.

I believe all have contributed to resolving the issue. I'm still not 100% sure if the remaining misalignment of layers is due to:
- an inconsistent diameter for the filament (varies between 1.71 and 1.73mm),
- wobble on the z-axis, or
- something else?

I've attached a photo of the results given the above settings. It looks rough in the photos but is actually quite good with only really tiny blobs (the z-height of the piece is 10mm for scale) but the layers are not well aligned on all surfaces (seems to be inconsistent though with some surfaces smoother than others). Note: The infill is set to 25%.

If the problem were inconsistent filament diameter, wouldn't the problem manifest equally on all surfaces? If the problem were z-wobble, wouldn't the bulging areas on one side correspond to inset areas on the other? With the prints I'm getting, it appears to be bulging on all sides at the same point, but not equally (or at all) on some surfaces.

I'll print out some parts to see if they reduce z-wobble. I've currently got two nuts with a spring connecting the threaded rods with the x-axis, though the rods aren't constrained at both ends.
open | download - Untitled-1.jpg (188.2 KB)
Re: Blobbing and roughness on vertical surfaces.
October 04, 2013 12:14PM

"If the problem were inconsistent filament diameter, wouldn't the problem manifest equally on all surfaces"

Is it the solid layers that have the problem? By solid layers I mean the ones where the infill is 100%, such as the top and bottom surfaces and diaphragms. If so then it is just a matter of having too much flow to feed rate, especially for the infill.

For layers that are not solid the flow rate is not that critical. If it is too much then it just means that instead of 25% you would get perhaps 35% solidity. If however it is a solid layer then instead of 100% you will get 110% solidity, which of course won't work as the material has to go somewhere. Depending on how much the excess is could cause anything from a slight oversize on the solid layers to some extreme blobbing and mess.
Re: Blobbing and roughness on vertical surfaces.
October 04, 2013 12:32PM
Unfortunately it appears consistently on surfaces with both a solid and hollow infill. The issue occurs all along the z-surfaces regardless of what's going on between them. I've recently printed parts to eliminate z-wobble, but the issue is still presenting itself.

I'm going to try replacing the x-carriage because at this stage, it can't hurt lol.
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