: hi john
: what did they use the casts for after that- more prototypes to modify? what
: did they make the new takeoffs from? f/g? more plaster?

: and how did they deal w/ undercuts? like on the station wagon roof the inset
: windows - how would you lift the cast off? several cast parts or other
: inserts?
: -mick

Good questions Mick,
Fist I should have said Ultracal in stead of Hydarcal. Both are very good.

This is how it works. A wood model is set up in an upright position that you want to make metal die from for stamping fenders etc., on a very large and extreamly accract granite plate. The model is prepaired as I describe for taking an Ultracal/Hemp cast from, and a set of wood parallel rails are fastened to the cast and paralleled with the granate plate. This was then bolted to a keller machine, I think it was called that was about 20 ft high that run a light touch tracer over the plaster surface and machined the die shape into the die metal. A man set in a chair and rode this machine high up in the air.

Then using the same location setup of the wood model that we took the plaster cast off of, we prepaired the model this time to take a fiberglass cast off of the same area and shape. This was used by die grinders that put blue chalk on the fiber glass mold we made and toched it to the machined die and slowly ground the die to get it exacly right.

Now the undercuts. To make an undercut so to speak, you had to make a die that pushed from the side. Some I seen were hinged. So you take your wood model and this time set it up on the granate surface plate so the side undercut was upright and you went to the same process. When a bend is made in sheet metal the engineers had to allow for metal flow. So the flange I mentioned you would build around your boat haul was not only to hold the plaster and hemp on a parting line but was also designed to allow metal flow trim waist that allowed a certain curve to take place without a fault in it during the pressing.

They also had to make large strong bridge like trusses to hold the die's for stamping. These were made with wood pattern with many complicated cores to make the many holes, room, or insets into the bridge work. This was later simplified by using styrofoam. A whole pattern was made of foam with all of the inset, inlet, holes, etc. cut in them. These were then covered in sand and the cast iron pored into the foam, melting it and filling the foam cavities to make the bridging. Very simple compaired to the way it use to be done with wood patterns and coreboxes that all fit together like a jigsaw puzzle. These were big and weighed many tons in metal.

The heavy cast were seperated and lifted by small screw jacks that we had that would lift the casts up slightly and kill the vaccume. This was early sixty's and it is a little fuzzy now. Then we had overhead crains to chain and lift the casts by the parallel rails I mentioned eariler.

Pattern making was so varried and different that you never stopped learning. I have 4 friends that have their own shops and one will differ greatly from the next in what they make and the skills they have. I'm not spell checking this.

John