Starting from a wooden carving , to sand casting in bronze. 90% copper 10% tin

Well, it looks nifty, be interesting to see it finished, know how it works.

I dunno, the right kind of bronze is supposed to be roughly hard as mild steel if work hardened. Wouldn't apply to cast though, and I wouldn't try some of the other traditional hardeners like arsenic. Where'd ya get the tin? Solder? Old pewter knicknacks?

Their is a reason knives in the historical record are designed the way they are. It certainly is a thought process tho. I think you have made a good start with your experiments.

I buy my tin nice and clean from rotometals.com   The trick is to cast the shape that's ready for pounding out and work hardening rather than the shape of the finished piece.

I got the copper from a nearby company which had pure copper scrap, and the tin from 97%tin solder 3% copper.

The edge is work hardened, i made a little jug which you can hammer and slide the edge back and forth to get perfect hits. 

Im now finishing the handle (zapote) and planning the next one, with a very different blade shape. This one is a bit thick, weighs 318g for a 9.75inch knife. I wasnt sure how strong it would be and left some margin of error for casting.

Here it is, complete with the handle finished, peened 3/16 brass pins, I'm quite happy with it as my first knife of any sort,  couple of things to improve for next time though. The edge should probably be further work hardened, I'm going to try 12% tin bronze to see how much harder it is, and maybe aluminium bronze eventually. The handle finishing and flattening the tang to fit the scales was the longest part of this project for sure without any grinder except an angle grinder which isn't ideal ( was flattened by hand).  

The edge is actually quite sharp, although sharpening by hand seems more difficult than steel- quick and easy to dull it accidentally, so far just been able to get it sharp enough to barely shave arm hair on a waterstone. Will try lansky to see if it's my technique

Strider knives made some for a military unit that had beryllium copper blades. Non magnetic, and non sparking for explosives work.  A friend had one. 

Very interesting, beryllium is however very toxic, I wouldn't want to make one.

Suggestion,

Google an occupational disease called berylliosis and check out the gory details.

Nasty stuff.

SLAG.

I know the hazards, we machined literally tons of it at the shop I worked at. With proper precautions it can be a wonderful alloy to use; color, strength, and heat treatable. 

Yes but many new folk reading this might not know the dangers or the correct procedures; so it will probably get mentioned every time it comes up.

Just recently finished my second bronze knife, (bday gift for my gf). 

-increased tin content to 12.4%, is certainly harder and is slightly easier to sharpen

- katalox wood handle

-currently re-lining my forge/foundry , got some 3200f refractory (unicast 70c)- should be more durable

Now just make sure you never get your girlfriend really mad at you.

On 3/4/2018 at 11:46 PM, Andrew Golabek said:

Just recently finished my second bronze knife, (bday gift for my gf).

Andrew-how has the unicast 70 been for You?

So far, my foundry has survived in nearly the same shape as it was when i started aside from some discolouration due to some silly experiments. I've successfully cast about 10 items so far ranging from 1lb to 4lb melts of classic bronze. The highest verified temperature I've achieved was approx 1400c during some experiments with ceramic it survived perfectly intact, which isn't a large surprise given the max temp rating of 3200f. Now onto its downfalls. There is a lot of larger grit in this refractory, no doubt giving extra strength, but mixing, and casting it without too much water by hand can be difficult. I couldn't find instructions for it online in regards to curing or water content, so just went with what seemed appropriate, as you add water to it, at a certain point it will become much easier to mix, and if there is any vibration it will act liquid. I think that is the ideal amount. Any higher, and from what I was told by the foundry supply is that it may not come out as strong. It sets like cement in approx 24 hours. The surface finish can vary depending on how well it was done from glassy smooth to very gritty with air bubbles on the surface. Firing it can be done relatively quickly once it has been dried with a low flame. 

On 1/7/2018 at 11:06 AM, Nobody Special said:

Well, it looks nifty, be interesting to see it finished, know how it works.

I dunno, the right kind of bronze is supposed to be roughly hard as mild steel if work hardened. Wouldn't apply to cast though, and I wouldn't try some of the other traditional hardeners like arsenic. 

Copper + Arsenic is called arsenical bronze and as far as I know was once of the first types of bronze. A good copper/tin bronze can be harder than wrought iron or (I guess) very low carbon mild steel. The problem in the Bronze Age was that a given Kingdom might have copper mines but not many tin mines. Iron was not a hard (or I have read in history books called not a strong) as good bronze BUT if you found iron ore you did not need another metal like tin. As far as I know all bronze items start as a casting and then can be work hardened after that. 

Also the reason you don't find many old broken bronze swords at Bronze Age sites is a broken bronze anything could be re-melted and re-cast. 

My latest knife has 13% tin, and 0.1% I think of zirconium added. The zirconium is a grain refiner for this type of copper alloy, and also increases hardness.

my casting process has also improved quite a bit, there is zero visible porosity on the last knife.

The knife looks really nice and glad to see you dialing in your process.

arent you adding a de gasser?

7 hours ago, Steve Sells said:

arent you adding a de gasser?

Like Beano?

I didn’t use a degasser, I followed some of the recommendations in the ASTM copper alloys handbook for casting bronze alloys with tin.

Some of the most important things I make sure of

-the sand must have the proper moisture content, just enough to lend the mold strength, but not enough to cause water and subsequent hydrogen and oxygen porosity

-I use ground charcoal for deoxygenation, you can’t add too much. 

-better results may be obtained if it is the second time melting a piece of freshly alloyed metal (the first time from many small pieces seems to have more porosity) not sure if this is 100% true, but it might be.

-cast quite hot, I think around 1100c, when you touch the surface of the bronze it should be shiny and very liquid not viscous and not with an oxide layer. This is very key to casting thin items.

-I’ve also tried degassing with a green stick of pine. Not sure how this works but the handbook mentions it and it seems to work.

-sprue and gate must be properly formed, follow the guidelines in the handbook, later I can update the exact measurements of mine.

Here’s a picture of one mold half.

75 grit silica with 10% bentonite

looking to get some 125-150 grit to add in as well for next casting

 

On 1/18/2018 at 9:59 PM, ThomasPowers said:

Yes but many new folk reading this might not know the dangers or the correct procedures; so it will probably get mentioned every time it comes up.

Mr. Thomas makes a very good point. There may not be a "safe" level of beryllium that once can take in without ill effects but the fact of the matter is someone may be exposed to a small amount of something and feel a little bit "off" and think that it was no big deal. There are a number of chemicals like lithium carbonate that have a VERY narrow therapeutic range meaning the "goldilocks zone" of do nothing, improve health and become toxic. If anything else I am always reminded of the words of Paracelsus (Philippus Aureolus Theophrastus Bombastus von Hohenheim) "The dose makes the poison" (Latin: sola dosis facit venenum). The fact that people are sickened by fatal water intoxication proves the point.