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I'm not sure what the technical term would be, I've found loads of useful tips in the past for problems, but I can't get to the bottom of this one.  It's possible I might have asked this before I've had the issue for a while now.  But my head is a sieve and I've had a lot on, so who knows!

 

When printing upright cylinders, say under 10mm, I get awful ringing around the circumference as if the outer layer isn't being printed in the right place, each layer is slightly different and the results are horrible.  Make the cylinder larger and the problem goes away.  The problem is most pronounced with nylon (Ultimaker) but is also noticeable with other materials.  Straight edges, slight curves, overhangs, all beautiful.

 

I've tried slowing the print speed, more and less wall thickness although I need at least 2mm thickness really.  These particular cylinders have a hole through for a bolt, but it makes no difference if they are solid with infill, or tubes.

 

Apart from changing the wall thickness and speed all the other settings are the Cura default for Nylon Fast 0.04

 

Any ideas?  

Many thanks.

Edited by Clancey
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Hi @Clancey , thank you for your post.

If you're not entirely sure about the technical term, it would be very helpful if you could include some photo's. Could you also add which printer you have using a tag? (you can find them under the title of this thread).

 

But based on your description, maybe the layers just don't have enough time to cool down? Have you tried lowering the temperature?

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I assume that when you say make the cylinder larger you are increasing the diameter, not just the height, yes?  If so then I agree with @SandervG it is likely cooling but without settings or pics it is just a wild guess. You want your layer print time to be say at least 10secs if reducing your extruder heat does not work. If need be print 2 or more copies to achieve this (all at once mode).

It may be that you are going too fast with a small diameter, although you say you have reduced the speed - from what to what?

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If this is the effect you get (see photo), then it is lack of cooling indeed. The ruler shows mm (small lines) and cm (numbers). This is most notably when printing 100% filled models.

 

My solution usually is: print multiple models at a time, or print sort of an "inverse" next to the real model, so the total amount of printing time per layer is always the same, and the time is long enough to provide good cooling. And print cool and slow. Using the option "minimum layer time" alone is not enough in my experience: then the filament sits longer in the nozzle, heats up more, and gets more liquid. This does not really reduce the amount of heat the model needs to dissipate, and the hot nozzle is still sitting on top of a tiny model, is radiating heat, and thus preventing cooling. The nozzle has to move away from the model *and* print something else, so the nozzle-flow is as constant as possible, and the heat source is far away from the part to cool.

 

DSCN5605b.thumb.jpg.2a696904daa58d988117c2f266bd4594.jpg

Effect of not enough cooling time. This should have been nice cones.

 

dummy_inverse_block6.thumb.jpg.2bdb2396588983363b48127ee12d8174.jpg

This picture shows the theoretical concept of printing an inverse dummy next to a tiny real model.

 

dummy_cutout2.thumb.jpg.750722bab5fa1c22a5e38d2a5717ab5b.jpg

This is part of a real design, at the left. At right in pink is the dummy: this dummy only needs to provide extra cooling time while printing the tiny top part of the real model, so it is hollow where no cooling is needed.

 

Putting a desktop fan in front of the printer, at its lowest speed, and at some distance, also helps to gently remove excess heat and improve shape for my models.

 

Depending on your models and materials, lots of similar solutions might be possible. The dummies are waste, but maybe you can design them into some little toys the kids can still use? Like houses for Monopoly, pieces for other board games, or bricks to transport in their toy cars?

 

But in your case the cause could still be something elso too. Such as: too many circle-segments in a too short time for the printer to handle, if the STL-file from which the gcode-file was derived, contained too much detail. Maybe other causes too.

 

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