## Re: [diy_3d_printing_and_fabrication] Re: shrinking rate

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• ... hello all, I m reading this group since a long time but posted just a few, so I jump in this discussion. As far as I know from my work, shrinkage goes with
Message 1 of 12 , Feb 16, 2013
• 34 KB
At 04.51 16/02/2013, you wrote:
>
>
>I think that if the resin has a linear shrinking
>rate then the hole shoud get bigger as the
>outside of square would get smaller by the same amount in percentage.
>i remember working with some bondo resin in the
>past and had the same problem and never found a
>good explanation on resin shrinking on this kind of odd shrinking.
>i don´t think light bleeading can be account for
>it. if that was the case the square would always get bigger not smaller.

hello all,
I'm reading this group since a long time but posted just a few,
so I jump in this discussion. As far as I know from my work, shrinkage
goes with material volume, not on overall
dimension, it works kind of both ways. If you
have a closed volume it will shrink of a % overall,
but if you have a hole in it, it will shrink both
in overall dimensions and "wall" thickness. So
the correct solution maybe a combination
of resizing and offset. Attached an image to
explain shrinkage directions. Also take in
account that thicker walls lead to bigger shrinkage
so the outside square also gets distorted by a
little bit if not supported by previous layers...

ciao,
Marco.
• Thank´s Marco i´ve measure the part and wall thickness is the same on both parts(normal and scaled part)it makes sense the more volume the more it will
Message 2 of 12 , Feb 16, 2013
Thank´s Marco i´ve measure the part and wall thickness is the same on both parts(normal and scaled part)it makes sense the more volume the more it will shrink. I think it won´t matter if I´m printing a box like with thin walls (scaling the part by the shrink rate) but it will make a big diference if i´ve a part that has both very thick wall and very thin wall on it.
I did print a part that was like that and it got smaller on thick walls then on thin walls thus deforming the part by a considerable amount.
i think the best thing is to keep all the walls the same thickness using a shell on the cad.

--- In diy_3d_printing_and_fabrication@yahoogroups.com, Bedo <bedo@...> wrote:
>
> At 04.51 16/02/2013, you wrote:
> >
> >
> >I think that if the resin has a linear shrinking
> >rate then the hole shoud get bigger as the
> >outside of square would get smaller by the same amount in percentage.
> >i remember working with some bondo resin in the
> >past and had the same problem and never found a
> >good explanation on resin shrinking on this kind of odd shrinking.
> >i don´t think light bleeading can be account for
> >it. if that was the case the square would always get bigger not smaller.
>
> hello all,
> I'm reading this group since a long time but posted just a few,
> so I jump in this discussion. As far as I know from my work, shrinkage
> goes with material volume, not on overall
> dimension, it works kind of both ways. If you
> have a closed volume it will shrink of a % overall,
> but if you have a hole in it, it will shrink both
> in overall dimensions and "wall" thickness. So
> the correct solution maybe a combination
> of resizing and offset. Attached an image to
> explain shrinkage directions. Also take in
> account that thicker walls lead to bigger shrinkage
> so the outside square also gets distorted by a
> little bit if not supported by previous layers...
>
> ciao,
> Marco.
>
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