Knife from file-fire pit forge-couple questions

R

Railrider1920

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I have been reading up on making a knives from files. Since I had a few old ones, I thought I would give it a try. I dug a small pit and put a couple of pipes into it from the side for blowing in air. Made a fire in it, added store bought charcoal and waited until every thing was going good and really hot. I had added the files into the fire. They were warming up along the side of the fire prior to this, along with fire brick and a 2'x2' piece of 1/4" steel.

After they were in the fire for a few minutes I hit the blower (shop vac in reverse) and let it get hot again. Then I covered it with a few fire bricks and the small piece of sheet steel. Then I covered the whole thing with dirt. When it was covered, I hit the blower for a little while longer to get it hot again. The mound started to smoke. It was pretty cool looking. Anyway, after heating it up, I removed the pipes and covered up their holes. It got hot enough to warm up the top of the soil. It sat there like that over night. The next day I took them out. Two of the files had slight bends in them. I did it again the next day, just not quite as hot I don't think.

Ok, now a few questions: The files that were bent, one of them was almost straight after the second firing (a 3/16-1/4 thick, 16 incher). The smaller ones still have a slight bend in them. If I heat them up slowly with a forge burner and then put them on a flat surface with weight on top of them, when they are cool, think they will straighten out?

I really don't know how hot they got, the first time or the second time. They did get red though. If I can work the file on them and take off some metal with out too much work, think they get soft enough?

OK, can you tell I'm a green horn?
Thanks,
Rob

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Interesting process there. Just need a pig and you could have a Luau:D.

First I think your fire got way to hot. You probably have extreme grain growth on your files. There is no way to control the heat in your setup. What I would have done is wait until later in the evening when it is getting dark out. This way you can see the heat more accurately. Heat up your charcoal (I hope you are using the lump type not the briquettes) get a good bed going with the air going. You might want to find a way to regulate the airflow. A vacuum exhaust full force is way to much air. After you have a nice pile of coals going put your file into the pile. It should have a good 2-4 inches between the file and the air blast. Put a nice layer over the file and heat slowly and evenly. This is were the air regulation comes in handy. Bring the file up to non magnetic normalize (cool in air) repeat and put it into a fireproof box full of vermiculite. This will cool slowly for the next few hours and give you a partial anneal. About the only way to get a full anneal is to do it in a controlled furnace. This will give you an easily workable material without excessive grain growth. Good luck and keep us posted on your progress.
 
I'm sure they're soft enough. You can probably straighten them cold, but definitely with heat. The question will be if they bend again when you heat treat them. I'm guessing that they will. One might also just grind the bend out if it's not terribly dramatic.

How do you plan to heat treat them after you've made them into knife blades? If I were to do this sort of thing, I'd build a small forge and anneal them in perlite. You can get it at WalMart in the garden center for dirt cheap, put it in a bucket and then heat up your steel in the forge and bury in perlite. Then you can use the same forge to do your heat treating.

Could just heat to non-magnetic or you could try and watch for the colors. Neither is particularly accurate, but both will work for making a knife. There's a lot of variables using old files and colors or magnets, but one works with what one has.
 
I agree, I think I did get it too hot. I just got carried away. I did have a hair dryer out there for a while instead of the shop vac. I was having "fun with fire". My wife was nervous about it. She did mention putting a pig shoulder in there too.:D I'll probably send any blades I make out for HT until I have something fairly reliable here at the house.

I will be building a forge with a gas burner. I have a burner I made a few years ago. I think it is 3/4" pipe with a flair on it. I'm trying to decide weather to build the forge from a couple of coffee cans or from an old spare air tank. with the spare air tank, 1" of ceramic blanket and 1"- 1 1/2" of refractory cement would give me a working area of about 7". I'm leaning more towards this one instead of the coffee cans, but I'm not sure. Any suggestions?

Thanks
Rob
 
Make the larger forge. I would put 2 layers of kaowool and 1" refractory giving you a 5" chamber. It is plenty large enough for most work and won't cost as much to heat.
 
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