Printing Very Skinny Parts

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2YRRAH
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Printing Very Skinny Parts

Post by 2YRRAH »

Was trying to print the top section of the gCreate 50's rocketship. It has a very skinny probe/pint to this part. The print was great until it got to the skinny part as seen in the first photo. Appeared to be overextruding. I could see the noozle mushing around in the soft plastic so during this print I reduced extruder flow to 90% and temp to 120 from 128. Didn't seem to help so reduced flow to 80%. May have helped a bit, especially near the top but top ball was still a mess.
20160206_182344.jpg

I took the file into my 3D app and cut the spike off to print separately since I think the lower portion of the print looks quite good. I'll just glue the spike on when I get it printed properly. Second photo is just the spike portion at 75% flow, heat at 220. I also set the restart on the retract setting to 0mm. Still not good.
20160206_182344.jpg

When I'm having difficulties finding the best settings for things I will often set them to extreme values to see what happens and adjust my way back something that works. So I set the flow rate to the minimum that Repetier Host will do (50%) and tried again. Photo 3 is the result. Better, but the ball is still bad. I likely will just cut the ball off and use as is.
Photo 3
Photo 3


So does anyone have any advice when printing parts that include some very skinny sections, besides what I have done? Unfortunately, Slic3r does not allow you to designate different areas of the print for different flow rates that I am aware of so that needs to be done manually during the print.

EDIT:
Sorry, I don't know why the photos came in sideways, out of order and with the first one duplicated.

EDIT 2:
Oh yes, I should have mentioned...Siver ABS, .5 noozle. 20mm/s perimeters. Layer fan was at 100% for all of the spike printing.
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Photo 2
Photo 2

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Captain Starfish
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Re: Printing Very Skinny Parts

Post by Captain Starfish »

There's a bit of a range between where ABS starts to slump and where it's hot enough to extrude. On big prints, it's no problem - the start of this layer has time to cool down past the slump temperature before the nozzle returns to it to start the next layer. On small parts, though, the next layer gets started before this one has solidified properly and it just collapses in a big slaggy mess.

Two ways around it spring to mind:

1. Set the minimum layer time. Usually this slows the print speed down which is fine for a lot of things but, on a narrow spike, it doesn't help at all because the nozzle is still close enough that things won't cool down. There are other options in Matterslice and probably other slicers that will print the layer then move the hot end away to some parking spot for a pause, then come back for the next layer. That's what you want.

2. Install a layer fan to cool the plastic down as soon as it leaves the nozzle. Ignore all the bitching you'll hear about ABS and layer fans, if you're running the nozzle hot enough you'll hit a nice balance and can leave that fan running all day. Or just switch it on for the skinny bits. Note: the layer fan is a massive bonus upgrade if ever you're bridging without support. Massive.

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Tincho85
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Re: Printing Very Skinny Parts

Post by Tincho85 »

I agree with the cap.
To solve this I would do:

1. Layer fan for this situation only. Abs needs a previously heated layer, if it's too cold it will delaminate.

2. Print 2 of them at the same time or print a simple tower of the same height next to it.
Martín S.

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thedoble
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Re: Printing Very Skinny Parts

Post by thedoble »

Yep you need to cool it down more. When I'm struggling I will just use some old PC fans I have lying around and point them at the print bed. You might struggle a bit with ABS though.

The tip about moving the nozzle away after each layer is the best, but your slicer needs to support this. You could probably do it manually with the g-code if you're willing to take the time.
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IMBoring25
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Re: Printing Very Skinny Parts

Post by IMBoring25 »

A before-layer-change gcode that moved the nozzle to an arbitrary location away from the part and added a dwell would do the job but then you'd have to deal with the ooze issue. A basic sacrificial cylinder the same height as the part would probably be the easiest thing to do.

nebbian
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Re: Printing Very Skinny Parts

Post by nebbian »

I printed this exact item last week in ABS.

The secret for small parts is to waft a small weak fan across the build plate. Yes, even for ABS. I have a small USB powered fan that I set up a good 30 cm from the edge of the plate, on low power. You just want a very gentle breeze across the plate, not a hurricane. Just a gentle zephyr.

Mine turned out pretty well, I was surprised at how nicely it turned out tbh.

magicmushroom666
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Re: Printing Very Skinny Parts

Post by magicmushroom666 »

As mentioned try printing 2 of them side by side. Also I use a min layer time of 15 seconds which seems enough to stop melting as long as the head has another part to go to.

2YRRAH
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Re: Printing Very Skinny Parts

Post by 2YRRAH »

Thanks everyone for your quick, thoughtful replies!

My layer fan was on and I had set the layer time to 10 seconds but everyone who mentioned it is right I believe... its the constant contact of the nozzle of the with the plastic that is the big problem.

I will try both suggestions to alleviate this...a second spike and a sacrificial tube, and post my results.

Thanks again

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