Printing Overhangs with ABS

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eric_german
Posts: 48
Joined: Sun Jun 09, 2013 3:31 pm

Printing Overhangs with ABS

Post by eric_german » Mon Jun 17, 2013 7:21 am

I am getting my new TAZ up and running and trying to print the following object:

http://www.thingiverse.com/thing:104987

here are some terrible cell phone snap shots:

http://imgur.com/a/TqOP6

The object has about a 53 degree overhang and filleted / rounded edges. I know I could break the object up in different ways and acetone weld / epoxy the pieces together, or rotate the object 90 degrees in x and use support for the cylinder bits. but right now I am trying to figure out what sorts of geometry I can and can't print.


I am using natural ABS from lulzbot and have tried a few different slic3r configurations, including the high_quality.ini provided courtesy of lulzbot. All settings with 230 C hotend and 110 C bed.

also i've tried this setting, with a 40 layer raft thinking my abs was getting too hot so I needed to get it off the bed a little bit :


; layer_height = 0.25
; perimeters = 4
; top_solid_layers = 5
; bottom_solid_layers = 4
; fill_density = 0.15
; perimeter_speed = 180
; infill_speed = 180
; travel_speed = 200
; nozzle_diameter = 0.35
; filament_diameter = 2.89
; extrusion_multiplier = 1
; perimeters extrusion width = 0.39mm
; infill extrusion width = 0.39mm
; solid infill extrusion width = 0.39mm
; top infill extrusion width = 0.39mm
; support material extrusion width = 0.39mm
; first layer extrusion width = 0.47mm

I've also tried a similar, slightly slower configuration but with support material. The support structure seems to hurt more than help as the hot end tip drags across the part's corners as it builds the support.

I think one solution would be to build multiple objects at once to make sure the perimeters cool, but really after like the fourth layer of this object the rounded corners have already begin to warp up and the hot end starts to bash against the cooled, warped plastic. I tried z lifting to avoid this without much success.

Any thoughts?

jebba
Site Admin
Posts: 689
Joined: Mon Mar 25, 2013 4:11 pm

Re: Printing Overhangs with ABS

Post by jebba » Mon Jun 17, 2013 8:21 am

Try printing at half those speeds and see how much it improves.

Also trying doing a skirt of 9999 layers or whatever, so it prints a heat shield around the part.

1013
Posts: 339
Joined: Thu May 23, 2013 9:56 am

Re: Printing Overhangs with ABS

Post by 1013 » Mon Jun 17, 2013 8:25 am

are you using the acetone/abs juice on the bed?

jebba
Site Admin
Posts: 689
Joined: Mon Mar 25, 2013 4:11 pm

Re: Printing Overhangs with ABS

Post by jebba » Mon Jun 17, 2013 8:30 am

Also, set your bed to 85C, not 110C. For the TAZ you just need 85C (or even less).

eric_german
Posts: 48
Joined: Sun Jun 09, 2013 3:31 pm

Re: Printing Overhangs with ABS

Post by eric_german » Mon Jun 17, 2013 8:19 pm

adhesion to the hbp isn't a problem. :)

i'm watching the part print very slowly with a skirt height. the skirt gives me an easy visual reference as to where each layer starts.

the overhang is failing when the extruder begins the next layer by crossing over (and mushing) the corner that is curling up.

i think i'll try randomize starting points.

it would be helpful if i could control the g-code enough to indicate at which corner of the part each layer starts. i wonder if simply rotating the part in slic3r might have an effect on this? i'm not sure if the tool path is written with the part's geometry relative to the x/y in the bed, or absolute to the part's geometry itself.

1013
Posts: 339
Joined: Thu May 23, 2013 9:56 am

Re: Printing Overhangs with ABS

Post by 1013 » Tue Jun 18, 2013 6:04 am

I have seen the mushing up corner affect before. It seems to happen on relativelly small geometries that print quickly. (I noticed it on the octopus, and other small parts).

I suspect that the ABS does not have enough time to cool before the next layer is applied, and then the next layer adds hot ABS and it cannot cool again. Perhaps you could adjust the "use cooling" feature in SLic3r so that it slows down more. or try a fan on the print....or just simply slow the print down with the overrides.

jebba
Site Admin
Posts: 689
Joined: Mon Mar 25, 2013 4:11 pm

Re: Printing Overhangs with ABS

Post by jebba » Tue Jun 18, 2013 8:08 am

I mentioned this to Alessandro (slic3r author) and he said that he is actually re-writing overhang calculation in the current devel tree of slic3r. So some changes will be happening there too.

eric_german
Posts: 48
Joined: Sun Jun 09, 2013 3:31 pm

Re: Printing Overhangs with ABS

Post by eric_german » Tue Jun 18, 2013 8:58 pm

^^^

nice.

meanwhile, I slowed the print down quite a bit and added a tall skirt.

its not quite there yet, but its already looking a lot better!

idfarmer
Posts: 4
Joined: Wed Jun 19, 2013 7:43 am

Re: Printing Overhangs with ABS

Post by idfarmer » Sun Jun 23, 2013 5:03 pm

Thank you for posting this. I'm having the same issue.

eric_german
Posts: 48
Joined: Sun Jun 09, 2013 3:31 pm

Re: Printing Overhangs with ABS

Post by eric_german » Sun Jun 23, 2013 8:12 pm

i'm also trying to print with fewer vertical perimeters.

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