Casting Bronze

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Knifemaker / Craftsman / Service Provider
Joined
Jun 11, 2006
Messages
8,633
I am considering trying to cast a few knife bits from bronze as I think it would be fun as well as an efficient way to conserve material. But I have a few questions as to what can be done. In the past I have used wooden molds to case lead based aloys and it works good. The wood chars but holds togather. But on bronze the temp is double and don't know if the wood would hold togather long enough for the bronze to cool. I know green sand and wax plaster cast is the most common way to do it but was wondering if wood could work to get a rough shape. Now the sand brings me onto my next thought. Can guards be cast around tangs. I'm working on a few seax blades and with the full flat grind all the way out and off the tang. This means the tang is triangle shape and that got me thinking about just casting a guard around it. My thought was burry blade in (green)sand with the tang and recosio exposed. Then shape the sand to your guard shape and cast. Guard would then be pressed off and cleaned up. I'm not expecting a super tight fit to the tang in the as cast state but that can be fixed with pressing.

Thanks guys for any tips you can provide
 
Folks also commonly braze slotted brass guards around tangs, but the amount of heat you'd be dumping into the blade by casting bronze onto it would totally change the temper of the blade. It's just too much heat with nowhere to go. Maybe you could get away with it if the plaid is clamped in between chilled plates or something, but it would be haphazard.

I believe aluminum's lower density and ability to transfer heat quickly makes this easier on the blade.

Have you considered lost wax sand casting? Simpler than plaster.



You could also try making makumegane out of it for forging it flat with nickel, brass and/or copper sheets.
 
I would cast the guard befor hardening the blade so it would not change the temper. I have not read much into casting honestly, I know the basics. But I'm guessing you use the wax in the sand and just cast and the metal melts the wax away
 
I'm wondering if I can shape the things I need out of foam.
 
I have cast multiple aluminum handles for knives and a cleaver as well as guards using a very simple "bucket with potato" method. Place a potato onto tempered blade near hilt, this protects from heat transfer into the cutting edge and can even be used for controlled softening of back of larger blades, for thin, pierce the potato. Use a 9 part sand mix to 1 part bentonite plus equal volume of water to bentonite. Mull (mix like crazy until fluffy). Pack the greensand around the blade and potato, tip down until you reach the guard area. For a simple cast on hilt, I simply put a ring of tin can around the casting zone, burn zinc off first or cast outdoors. Pack greensand around ring and pour. For a cast on handle, I use heat formed and belt sander tapered shapes plus a plug poured on top to allow for contraction as the metal cools. Complex and detailed handles can be cast using a model with cope and drag plus embedded potato or gelatin casing on blade. For aluminum handles a great finish is epoxy micarta wrapped around the handle, burlap, nylon, etc, dip in epoxy, wrap handle, then electrical tape into general shape and vacuum bag the assembly to compress. This produces a thin "skin" of fiber reinforced epoxy micarta around grip zone.
 
For bronze casting zinc vaporization is not an issue, but brass contains zinc which vaporizes out of the alloy during the melt. Although up to now I have melted in cast iron, I recently purchased 12 crucibles off ebay for under $50. For bronze temps I would use a quality crucible and lifter, I forge my own lifters or bend #9 wire for very small crucibles. Generic carbon crucibles are really cheap, $4 for small and $20 for huge stuff for very large pours. Will work on posting some pictures of potato bucket casting and end results.
 
I use steel mini propane bottles cut in half to melt stuff in. Get some white play sand and mix it with some ash and a little water. Carve your fittings out of foam from the dollar store, either the sheets that you can glue together and shape, or the plant arranging foam. Bury it with a sprue sticking out or just a hole in the sand. Take your time melting the bronze/brass or you will have lumps. You arent trying for precision and will probably need a bit of play anyway.
 
We just finished building a house and have loads of scrap foam. It's the pink/purple foam sheet that's 2" thick. Use it as insulation in places where fiber glass insulation was not practical. But it is nice light foam that cuts real nice not like the large (grain) stuff thy make packing material or cheep coolers out of. So just pack green around the foam and leave a sprue exposed. Then pour the bronze right onto the foam sprue. I'm not looking for super detail just a way to get a rough shape of the bits I want. I watched that sword making video and wow crazy detail in his cast guard.
 
You must log in or register to reply here.
Back
Top