Calculating ABS shrinkage when drawing.

[ahlstrominfo]

I'm trying to wrap my head around sketching things for printing in ABS, since it shrinks.

Should I calculate when drawing or should I just scale stuff in makerware when building it?

Have any good ideas?

[lasda]

While ABS shrink is real, I have found it not to be that big a problem.  I printed a part for a special plumbing valve assembly the other day and it fit perfectly without any consideration for shrink.  By fit perfectly, I mean it sealed and held air pressure as it was designed to do.  The part was about 5cm in diameter.

Note: they had the same part printed by a service on a much more expensive commercial printer and it was not as nice and did not work as well...

By the way: the biggest problem with ABS shrink I have found is the cracking between layers that can happen on bigger parts.  The shrink forces can be strong enough to pull the upper layers away from lower layers making cracks along the layer lines.  That ruins structural strength and the part changes shape.  This often happens after the part has been printed -- you can hear it happen while the part is cooling.

Maybe someone has comments about cracking after the part has been printed?

[Shawn]

I've never had to concern myself with shrinking. Even when doing
precision sized parts. In those cases I had to worry about tolerances
(0.2mm +/- 0.05mm in my experience - depending on environment, plastic,
what day it is, etc.).

Shrinking has only been an issue for me when dealing with large prints
that have thin walls. As the different layers cool at different rates,
some contraction happens causing stress. If the layers are not well
bonded they can separate resulting in cracks. To address this bonding
issue, I increase my fill when I have large thin areas. Or I slow down
the print significantly (from 120mm/s to say 50mm/s). There are other
ways for dealing with cracking as well - the history of this List has a
plethora of discussions on the topic. But, this delamination of layers
is the only place I've seen shrink come into play - and it's addressed
through methods unrelated to shrink.

Mind you, this is only based on my experiences... :)

Oh, I find my sizes may be thrown off a little if I include too many
shells. Usually only by about one shell width...

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[Joe Larson (aka Cymon)]

The place where I've had the most problems with shrink is when designing jewelry to a specific size. ABS shrink is enough that the ring loses one size, but that's easy to fix, just print one size bigger than you need.

If the part you're printing needs to be exactly a certain size and you've got a really well dialed in 3D printer then you can scale it up usually by 1.02 and counter act the shrinkage.

[GFischvogt]

I usually print Inside diameters .6mm larger than I want the to be and outside diameters .6mm smaller (.3 mm per wall) Since I use maker ware and I do not have the packing density calibrated, my machine lays down a bead of material wider than the nozzle orifice (.4mm). I'm not trying to accommodate for shrink, rather squeeze out that the machine doesn't account for. This is why my adjustment is a fixed offset not a percentage like you would use for shrink.