Advice on building another forge

[Mende]

Hello everyone!

Don't know if y'all remember me, I've been really busy with university and put forging and posting here on hold for a long time.
Anyways, I'm in for a 5 month long summer vacation (got lucky with the exam schedule and finished school early) and I have a couple of long sword blades that need some heat treatment.
The problem is the longest one is 4-5 feet in length and my forge can only keep 1 foot hot for any ammount of time. Here's where I need you to throw some ideas my way.
I was thinking of simply making a V shapped trench with 3 tweers/blowholes and filling it with charcoal and praying.
How I wanna do this is by digging a 5 foot trench in dry ground, line it with fire brick and bring a minimum of 3 pipes blowing air into the whole thing. I'm hoping that will give me a long enough focal point to keep the entire length of the blade hot (by sawing it back and forth through the fire) until I can dunk it some oil.
The blades are made from some truck suspension leaf springs, so the quench tub will be filled with oil.

Any thoughts on the design and procedure? Keep in mind I'm on a bit of a budget and I can't really afford expensive equipment or materials. sketches and criticism always welcome! :D

[don't tread on me]

I don't think you need the blowers, I saw a kid on youtube make a sword that way and it was vary flexible.

[ThomasPowers]

You do seem to have a perfect use case for a simple trench forge: long heats and not used very often.

I don't line mine with firebrick and I made a long tuyere from some black iron pipe that I drilled a large number of holes along the "top" side. This makes for a more even heat that having several spot points---you really need to have a deeper forge to help the spots "blend together" compared to a linear tuyere.

Using charcoal you don't have to blow it very hard. I would: start the fire and let it all heat up. Blow it slightly to get the temp up. Stop blowing and insert blade and let it "warm up" and then do a slow blow to bring the fire and blade to hardening temp.

Be sure to have enough quenchant so as to not have a problem with it overheating! (I assume you will be using oil?)

I used to backfill my trench forges with gravel to "hold them" till the next time.

[Mende]

You do seem to have a perfect use case for a simple trench forge: long heats and not used very often.

I don't line mine with firebrick and I made a long tuyere from some black iron pipe that I drilled a large number of holes along the "top" side. This makes for a more even heat that having several spot points---you really need to have a deeper forge to help the spots "blend together" compared to a linear tuyere.

Using charcoal you don't have to blow it very hard. I would: start the fire and let it all heat up. Blow it slightly to get the temp up. Stop blowing and insert blade and let it "warm up" and then do a slow blow to bring the fire and blade to hardening temp.

Be sure to have enough quenchant so as to not have a problem with it overheating! (I assume you will be using oil?)

I used to backfill my trench forges with gravel to "hold them" till the next time.

Aha . .so long pipe with holes in it .. . PERFECT - I don't have many blowers as it is. I will indeed be using oil ( don't know the steel and don;t want it extra hard - especially as I don't know how to temper ) Thanks for the input. Real helpful!

[pkrankow]

Temper by heating a piece of 1/2 inch rod and placing against the hardened steel you want to temper. Watch the color run. You need to polish the hardened steel with some 100 grit sandpaper so it is shiny first so you can see the color. You want the spine to be blue and the edge clear to light straw for many applications.

http://www.anvilfire.com/FAQ-article.php?bodyName=/FAQs/temper_colors_hardness.htm&titleName=Temper%20Colors%20and%20Steel%20Hardness%20:%20anvilfire.com

Using a rod you can temper a small section at a time on a large piece. Re-tempering an area will not cause harm. Work with an L shaped rod, about 1/2 inch round and about a 4 inch end heated up to VERY HOT although for a thin part dark red may be all you need to transfer heat well. Make sure your part is cleaned and bright or the color will not show and run. The color is is an iron oxide layer that forms and thickens, the straw is iron (III) oxide and the blue is iron (II) oxide.

Phil

[ThomasPowers]

For a sword blade, rod can be tricky to use if there is a center spine. A piece of flat, preferably with a shallow groove in it works better.

[pkrankow]

For a sword blade, rod can be tricky to use if there is a center spine. A piece of flat, preferably with a shallow groove in it works better.

Learned from experience? I'll have to remember that one.

Phil