On Tuesday, December 21, 2004, at 07:54 PM, Bill Daniels wrote:

Larry Jackman sez:

I must correct this one statement. There is always

shrinking in brass

investment casting. It is 1 1/2%. Melted brass

always shrinks I cast

brass for 20 years and it always shrinks

I remember talking to Stan Schwedler up in Phoenix
some time ago (he and his brother Sheldon run Coronado
Scale Models) and he explained the process like this.
You built a master 8% oversize. There is 4% shrinkage
per generation and you ran parts in two
generations...one to build up enough parts to build up
a sprue, and a second to cast the sprue. So you build
your masters 8% (two times 4%) oversize to compensate.

=====
Bill Daniels
Tucson, AZ

You are going to end up with some over size parts if you use 4%. I learned the casting process from Raoul LaBlank who set up PSC in the casting business and also owned and ran West Earth a jewelry Manufacture company in Seattle Wa. and also picked up pointers from PFM/PIA. All the brass they used shrank 1 1/2%. Maybe Stan was using a different kind of brass so before you start your Patterns find out what your caster is going to use. BTW before I got into doing for myself Kelly Morse was my Pattern Maker.
One more thing some rubber will shrink. Maybe that is where they are getting 4%. But if you use Dow-Corning J type RTV and leave your part in the mold for three days before cutting it open there will be NO shrink in the rubber mold. So I am talking from MY experience and so I suggest you take no ones word on this and go to the caster that is going to do your work and follow his suggestions.
The old saying "To many cooks spoil the broth".
BTW My experience is I started casting in about 1985 and continued until I moved to Florida in the year 2000. I also taught Larry Burt of Smokey Valley Railroad Models how to do Investment casting.
Also I was told you can not cast against Rotation. But I did it all the time and so did my teachers.
If you need any thing more from me contact me direct.

Thank you
Larry Jackman
ljack70117@...
I do not care who you are fat man. Get that sleigh and reindeer off my roof.