Metal Casting Zone

What is the shrink rate for 356 aluminum. I need to duplicate some aluminum parts for an antique marine engine and need the information for the pattern.

Thanks

Bob Price

welcome bob. normally 1/16 to the foot. shrinkage can be 0 on small parts if you use gravity casting. any chance of some pics of what you want to cast!! how much machining needs to be done?? how fine a detail are you after???

Thanks xl - the parts are cover plates for the crankcase openings on a 1917 Buffalo two cylinder engine. Nominally 6.5 x 8 with an average thickness of .19 to .25 inch. The outside surface has some cast lettering about 0.06 high. My docking station for my cell phone quit last night so I can't send some pictures till I get that fixed.

Several people have told me that a foundry can use the original part as a pattern but that would just duplicate some of the less than good features of the parts. I can make a 3D CAD model, expand it per the shrink rate and then send it to a company that can make a plastic rapid prototype part that could be used for a pattern.

Comments?

And again, thanks for the response

Bob Price

that sounds good. i make my pattern from the original part. once i have the part i clean it up. if detail is missing i use car putty and a die grinder to sharpen up the image. for a simple plate if i needed to add some thickness i glue some carboard onto it. another trick i use is to make the mold and as im removing the pattern i just press it in a bit more to add thickness. if you poured them vertically shinkage wont be a problem but horizontally it will be. if a bit is broken it can me repaired in the molding . ive used broken cast iron parts as patterns .

The advice about pouring the parts vertically is great to know. Is that because the incoming liquid metal acts as a riser to control the shrinkage?

And applying some cardboard is neato although there is a tricky return surface on the part that allows it to hook over the edge of the opening so it can be retained by just two fasteners at the top.

I'll keep you posted as the project proceeds. By the way, what is the source of the information about the shrinkage rate: I searched all over the place and could not find a straightforward source?

Thanks muchly.

Bob

why not cast in brass? less shrinkage and better corrosion resistance. looks purdy too.

see if you can obtain a copy of dave gingery "charcoal foundry" page 34 shows how a simple shrink rule can be made. you may be able to download a pdf! or get one from lindsays. a few members here have copies and we swear by the book as a general starting point.to pour them vertically you will need a special flask like i have. i can pour 7 or 8 inch square and 3/16 thick with ease.

Well when you are restoring something it is best to make it like the manufacturer made it.

This is true, im surprised that it was al on a marine engine. I guess thats why it needs to be replaced. Welding not an option either? and are you trying to match the surface finish as well? If not trying to match the surface finish and you do have a pattern machined then why not do a wax pattern and do lost wax casting. Im In love with lost wax right now lol

a hobby foundry near here cast metal signs but they cant get down to 1/4 in aluminium. cast iron being hotter seems in times gone by ok at that thickness.i tried but it wasnt till i started vertically that i had success. its very disappointing to open a mold to find it half filled. its a pity you arent close by. im into vintage machinery as well.