bronze carving mallet

[Clodbuster]

So I want to create a bronze carving mallet for detail carving of wood/stone lettering.  I've used several nice little numbers other folks owned consisting of pretty wood handles attached to round brass heads like this:

 

These work very nice and would be a good project for me to develop my casting and turning skills on.  This one is about 6" long and 1.25 lbs total.

 

What I need is a critique/verification of my approach for casting it.  Here's what I have available:

• Bronze plumbing check valve body, stripped and cleaned for raw material.  There is sufficient extra to allow for dross and machining losses.
• A #3 glazed graphite-clay crucible rated for 2500 F.  It has never been used.
• A charcoal/coal hand blown forge.
• An oxy-acetylene torch with a huge rosebud.
• A large propane weed-burner style torch.
• Lots of firebrick.
• A simple open mold of the (oversized) pattern made from a 40:60 mix of talc:plaster of paris.  The mold is small as it was made in a cottage cheese container.
• Basic experience with plaster casting zinc alloy and sand casting aluminum.
• Full leathers, welding helmet with clear glass lens, foundry gloves and boot covers.

 

Here's the approach I am thinking of taking:

1. Fully dry the mold and crucible in the oven, starting at 150F and finishing at 500F for at least 1 hour.
2. Stack firebrick around the forge firepot to extend its height so that the crucible will be surrounded on all but the top side with burning charcoal.
3. Light the fire and place the valve body in the crucible ensuring that it won't expand and put pressure against it.  Place the crucible in the forge and pack charcoal around it's sides.
4. Feed the fire with air and charcoal until I can look down and see an even melt on the bronze.
5. Remove crucible with preheated tongs and pour into still-hot plaster/talc mold.
6. When cool, remove part and machine.

If you have any critiques I'd appreciate hearing them before I start.  Also, I'm curious about the following:

Do I need a flux or cover for melting bronze?

Is it ok to use the same crucible for different metals (copper, bronze, aluminum, zinc alloy, babbitt)?

Is the forge the best way to heat this or would the propane torch be better?

Any suggestions on measuring/telling temperature?

 

Thanks for the help.

[Bentiron1946]

You would be just as well off to do as a sand casting since you have that experience as opposed to the plaster talc casting. Forget the weed burner, just doesn't seem to generate the number of btu's necessary for a good melt. Your idea of a charcoal hand blown forge should work but it will take awhile. Without a pyrometer there is not a sure way to tell except by color change. I used to pour by color when my pyrometer was out of order and poured when it was near incandescent in color about 2,300F. You can also get from a ceramic supply these temperature cones that melt at predetermined temperature ranges but I don't know how they would work in a melting furnace. And yeah it is important to make sure there is no condensate on any of the metal add to or poured into damp moulds, hot metal hurts like crazy, so full leathers is a must and make sure the laces on your boots is covered with three or four layers of duct tape, this keeps the little bitty globs from getting in there and causing havoc. Plumbing bronze? Yeah, I guess that they are using some silicone bronze in some check valve know, I have a very nice butterball ball valve, 12", center ball that is silicone bronze, been saving it for year for a special project. If you're sure it's silicone bronze it should cast up fine, pour temperature should be around 2,150f for best result. I have never used a cover for silicone bronze nor a flux but if it is red or yellow brass you will need to degas and a flux. It's been thirty years since I messed around with brass, nasty stuff to cast compared with silicone bronze, too much work compared to silicone bronze.

[njanvilman]

Not to throw a wrench into your casting plans, but why don't you just get a piece of 1 1/2" or 2" round brass, and machine it to the shape and threads/hole that will work.  I never like cast items where they are used for striking.  Especially on a homemade pour.  Your are going to need a pattern too in your above list.  And after your casting, machining will be the best way to clean it up anyway, so why not start with a better piece of metal.

[Clodbuster]

Thanks for the tips so far. 

 

I do have a thermocouple that I used for previous pours with pot metal, so I can check to see if it can handle the higher temps for bronze.  Good tip on watching for incandescence as well, I'll do that.

 

I already made the pattern (oversized for shrinkage/machining) and plaster mold.  I'll probably stick with that as it's made and I've had good luck with plaster to date.  I have lots of experience with plaster making rubber part molds, but little with sand molding, so for now it's kind of a devil-you-know type of thing. 

 

Point taken on it being easier to purchase round stock and the use of a casting for striking, but it should be fine for this application.  Although this is a mallet, I'm using it for stone lettering chisels, which are tapped so lightly as to render the head's brittleness almost irrelevant.  If I had a head of solid glass the right size it still wouldn't break as lightly as these chisels are tapped.  Also, like a lot of guys on here, I'm not doing this because it's the most efficient or cost effective way, I'm doing it for the learning experience and the enjoyment of making it with my own hands.  If I wanted to do it the cheapest/ easiest I'd just buy one.

 

What's the protocol on using the same crucible for melting different materials?  Is that ok or a no-no?

[Frosty]

I don't know the heat rating of plaster of Paris but don't think I'd like being around it when it starts popping, especially if molten metal is involved. If you do a surface or fine coat of plaster then bolster it with plaster and silica sand for strength and expansion resistance it may be good. Please forgive me I can't bring the proper terms to mind right now and it'd probably be a couple days post Christmas before the local caster could respond. He does ceramic investment casting but is a master of most all other techniques.

 

Personally I'd use a mix of fire clay (because I have a bag, not because it's the STUFF to use) and silica sand to green sand cast such a thing. I'd give doing the melt in a covered forge a shot as being simple and reasonably controllable. I'd use brick to make a small furnace structure over the air grate and not worry about trying to isolate the crucible completely. I'd flux with borax.

 

It's a pretty simple casting project if you have casting experience. The question to answer first is heat. What's too hot? I'd determine too hot in my gas forge by simply melting and overheating a bit of bronze in a hollow in a fire brick piece. Do this outdoors in a little crosswind in case dangerous fumes form but not blowing directly on the melt.

 

I certainly would NOT use crucibles for different metals, this is usually almost always a BAD idea. Then again I wouldn't use a "real" crucible for bronze, I'd weld a base on a piece of clean black pipe, forge a pouring lip and make a pair of tongs to fit safely, probably weld a little lip on the crucible so it wouldn't be likely to slip in the bits.

 

While I can't say anything about other's experience and or ability to undertake inherently dangerous new pursuits, this IS a blacksmithing site so inherently dangerous is the norm. be careful, wear PPE! Have someone on hand if you need help but out of the line of fire.

 

I'd take a shot at it but that's me and I could be wrong.

 

Frosty The Lucky.

[Bentiron1946]

Frosty, It's a good idea to use a crucible for each type of metal you pour, one for silicone bronze, one for nickle bronze, one for traditional bronze, what you don't want to do is use one crucible to do a pour in one metal and then the next time use it melt another alloy, you end up with a bunch of contaminated pours and no pure metals, this may not be important to the home founder but for a fellow trying to do a commercial business or even a half way decent job as a hobbyist you need to keep your pours pure. Yeah, a lot of guys I know use welded up schedule 40 black steel pipe for a one shot crucible and I guess that's OK if it's a one off but you just have got to be sure that it's well sealed or you got a real mess on your hands or should I say feet. I have use Plaster of Paris & silica sand as a reasonably decent investment but I use a steel ring to pour it in as it tends to crack and the steel ring(read short section of black iron pipe) keeps in intact so it doesn't fall apart during the pour. Cloudbuster is correct in getting it hot and driving off all the moisture before the pour, that way there is no popping and spitting. And so is Njanvilman, looks like it would just be easier to buy a hunk of brass and machine it down.

[Steve Sells]

remember many use the term brass ( copper and zink alloy ) and Bronze ( copper and tin alloy) interchangably.  The zink will off gas and not only poisons the air you are breathing, but changes the alloy quality so it also needs to be adjusted when melted.

[Bentiron1946]

Well, a brass could be called a bronze you know. There is a product I have had the pleasure to use on occasion that is call Manganese Bronze and it is really a brass or is it? It has a composition of 60-66% copper, 22-28% zinc,5-7.5% aluminum,2.5-5.0% manganese, 2.0-4.0% iron, 1.0% nickle, 0.25 lead and (wait for it) 0.20% tin. WE rally can't call it bronze can we because it's small amount of tin is far outweighed by it massive amount of zinc but when I bought it the name was Manganese Bronze not Manganese BRASS which is what it really is. Bronze on the other hand can be any of a number of alloys of copper and other metals including tin but not restricted to tin alone. Bronzes can be made with arsenic, bismuth, antimony, tin, silver, gold, silicon, well just about any other metal that will alloy with copper except zinc because when you use that you have made a brass. Oh yeah, one of the bronzes I'm using now that silver is so high is German silver an alloy of copper and nickle. The particular one I have right now has 94% copper and 6% nickle, looks looks pretty good too, just not Sterling silver.

[H&T]

I stock and use at least three types of brazing rods, "silicon bronze", "manganese Bronze", and "nickel bronze". Tradename is sifbronze. The nickel bronze is by far the most expensive