Shrinkage

[woodnut]

If you really want a shrinkage rule, just draw a standard 12" ruler in CAD, and then plot it to whatever multiplier is required for the various metals. You can print it on card stock and then laminate it in plastic.

Well now why didn't I think of that??

Thanks UNIcastings

For those of you who don't have a CAD program, attached is a PDF of a 3/16" shrinkage ruler.

John

View attachment 3:16 Shrinkage Ruler.pdf

 

[Rocket Man]

You typically need to allow for shrinkage especially on sand castings that need to be machined. The machinist hand book tells you about shrinkage.

I have made steel molds for casting large volumes of parts. The molds are like bullet molds they open and close with handles for small parts, larger parts clamp together. I heat the steel mold to within 100 degrees of the melt temperature of the metal then I can pour one part after the other for several hours. Shrinkage is exactly like the machinist hand book says 1.5 to 10% depending on the metal being poured. If you machine the shrinkage into the mold cavity the finished parts do NOT need to be machined.

 

[JorgensenSteam]

"If you machine the shrinkage into the mold cavity the finished parts do NOT need to be machined."

Huh?

It is my understanding that shrinkage allowance and machining allowance were too different things, with machining allowance being added to surfaces that need to be machined.

Not sure how you would use a part if you did not machine at least the mating surfaces.

 

[Dan Rowe]

Pat,
You need machining allowance with sand castings.

Rocket Man is using steel dies and die casting is much more precise than sand casting.
Here is a link to a die casting service that explains the tolerance that can be achieved with die casting.
http://www.castingreps.com/casting/die-castings.aspx

Dan

 

[JorgensenSteam]

Oh, I see that.

Very cool stuff.

Thanks Dan

 

[ksor]

But remember the shrinkage has to do with the kind of metal
you'r MELTING NOT the kind of material you'r using for the mold !