View Full Version : How much does ALuminum Shrink?

04-29-2007, 08:03 AM
I was wondering how much Aluminum shrinks while aluminum changes from a liquid to solid. Does the way you pour or the size of the cast have an effect on the shrinkage?

04-29-2007, 09:16 AM
Bulk is 2% or so, but that's solidifying point to room temperature. I don't know about the actual phase change...looks like it might be 5%?


Bob S
04-29-2007, 02:39 PM
I figure a shrink from my pattern to my casting to about .020 an inch or 1/4" per foot give or take depending on the shape of the pattern. Bob

Adam Ziegler
04-29-2007, 03:58 PM
Depending on the size of what you are casting.. .dimensions, and medium you are casting into... contraction can be negligible. With that said... I would go with what bob and tim said on ways to approximate the final result.

04-29-2007, 04:30 PM
We usually add aprox 3/16 per foot, The Patternmakers here will know what the standard requests are.


04-30-2007, 05:05 PM
Don't they make shrinkage rulers and tapes?

04-30-2007, 06:40 PM
Don't they make shrinkage rulers and tapes?


This company will custom make them what ever percentage you need.


05-01-2007, 01:02 PM
I would recommend multiplying all dimensions by 1.1 to 1.2% addition depending on size and internal coring

Edit* added variables

05-02-2007, 03:10 PM
Every pattern I have ever built for aluminum used 1/8" shrink.

That means that the aluminum will shrink 1/8" per foot.

The multiplier is 1.01041

So take your dimension and multiply it by the above 1.010416 and you will get the "shrunk" dimension. Build your pattern to that shrunk dimension and you will have a casting that will measure your original dimension.

Shrink rules make it easier.

I have heard some people using 1% (1.0100) as the shrink factor... it's damn near the same thing.

Keep in mind that if you have part that is much different in one dimension, that you may have to compensate for it. I.E. a very long, but narrow and thin part may require "more shrink" on the long dimension. But it usually has to be very dramatic.