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Fire Brick forges

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by KennyB, Sep 25, 2010.

  1. KennyB


    Jan 19, 2010
    I've seen a couple of designs so far on using fire brick and a propane or mapp torch inserted into a hole in a chamber formed by just one or several of the bricks.

    I'm wondering how problematic having the flame from the torch entering one spot is, and if you're just supposed to move the piece around and try to heat it evenly, or wait for the whole chamber to heat evenly or what.


    This one here seems to be small enough and simple enough for me to build, but I still wonder if the part where the flame enters will heat parts unevenly. Though that's more of a question with gas/torch powered forges in general than with the fire-brick ones. However, since I like the design of this one, I figured I might as well be specific and ask about it.
  2. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Well, the short answer is that a one brick/two brick forge is better than no forge. It certainly is cheap and easy to build.

    To answer your specific question about uneven heating...yes, that can be a problem. The blade must be watched, and perhaps moved in and out slowly to get a more even heating. For forging, a one bricker can work just fine. For HT it will take careful control of the amount of flame, the distance in or out of the port hole (where the torch enters the forge) and even movement of the blade.

    Letting the brick forge run for several minutes to fully heat up the brick interior is a good idea to get a more even heat. This is called pre-heat, or soaking the oven, and is a good practice with any type of forge or oven.

    Final sugestion...use a Bernzomatic JT-7 torch.
  3. Remyrw


    Jun 17, 2010
    I made a small forge recently and use it for HT of 1080, but I'm sure it could be used for forging with some adjustment. The burner is a high power weed burner positioned with the tube about 5" from the actual chamber interior, which puts it outside the bricks just barely. The actual nozzle itself is further back. I don't use it near full power either.

    Like Stacy suggests, the JT-7 is the most popular, but no longer being made and the replacements I could find were a lot more money and complexity. The JT-7 is still out there, just more rare and I couldn't find one locally so I went another route.

    Definitely have to keep an eye on things since it doesn't take long to heat up my 1/8" thick stuff. I keep it moving, and have positioned my burner toward the entry so the hottest area is not by the tip of the blade. I've only done two actual blades with it now, but a fair bit of fooling around to get a feel for it, so far so good. Both real HT's seem to have worked great.

    I have rearranged the front so the bricks that stick out on the left are going out to the side rather than in front, that gives me more room in front and reduces the heat on my hand and arm coming from the right.

  4. KennyB


    Jan 19, 2010
    Yeah, I'm specifically looking to use this for hardening. I suppose I should look at it more as a furnace than a forge then, right?

    One idea I had was to put another piece of firebrick with a bunch of holes cut into it in front of the torch flame so the flame would hit the brick and travel across that, but let the holes still allow heat into the chamber--just more evenly. I'm not really sure how well it would work, I might just buy an extra fire brick and test it, but how does the idea sound on paper?


    Yeah, I meant to ask in the other thread where you got your torch from. I'm sure there are places I could buy something like that around here since it's a pretty agricultural area, but wondering if you bought it from a specific store for a specific price.

    I still might try to find a Bernzomatic since that seems to be the defacto torch for this application. Are they very hard to come across on eBay?
  5. Remyrw


    Jun 17, 2010
    I didn't have any trouble finding the bernzo on the web, just at random places I didn't know so I figured I'd stick with my local source. A close friend, basically family, is in the mixed gas, propane and welding supply business and hooks me up at a good price on this stuff.

    The torch is just a standard weed burner, any farm/yard place should have them, though it's more commercial than consumer style. Mine still has the long wand style tube but it's easy enough to get a shorter one. HOWEVER, keep in mind that on propane it's reverse threading, so a regular pipe nipple won't work in most of these things. Plenty of solutions for that, from adapters to just having it cut and threaded the way you need. I got mine from my buddy, but there's nothing special about it, I wouldn't be surprised if walmart carries them in more rural areas. I got the adapter to run it off a 20lb tank as well, much cheaper supply that way.

    The 20lb tank brings me to my last tip on propane. Don't do tank swaps unless your tank is not looking so hot and you want a new one. Find a place that fills them directly and pay for what you actually get. Propane is much cheaper than most people realize, you're paying a lot extra for that tank swap and getting less in the tank because they don't fill them to even the usual safe level for those places due to how many are sitting there. One good hot sunny day and even the usual safe level might have lots of venting, and with that many that's a risk. Propane is a weird business, huge price variations from place to place and time to time. The price over time is not your local guy's fault, he's just passing along his increased costs, it's seasonal due to demand.

    Call around, find a commercial style place that sells a lot in volume. A fill up from them might be half what it costs from a gas station or through a tank swap.
  6. NStricker


    Feb 23, 2007
    With a one brick forge it's difficult to keep the flame off your blade, so you can't really avoid the hotspots. Two bricks are a little better because you can increase the chamber size a little more, make a rounder chamber, and get more swirling action.

    If you go the brick route, make sure you get soft firebricks (usually not as available as the hard fire brick used to line fireplaces & kilns). When you pre-heat your brick, do it slowly--you don't want to open up your torch full throttle from the start. If the interior heats faster than the outside the brick will crack. It will crack eventually anyway, but you don't want it to happen on your first run.

    I used a one-brick forge for about a year, but eventually built a coffee can type forge with kaowool and refactory cement. More even heat, a little bit more money, but more durable (though after nearly 2 years it is about time to reline the refactory cement). And, the chamber is still small enough that I still use my JT-7 Berzomatic torch with propane to forge and HT.
  7. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    Patrice's setup using a bunch of fire bricks ( they are cheap) is a superb way to make a take down oven. While not a professional setup, it will work.
    I would also suggest that you consider building a forge, or at least the burner. A burner can be made for probably $20 or less, and a whole forge for less than $100 ( $50 if your scrounging skills are good).
  8. Remyrw


    Jun 17, 2010
    Making your own burner would definitely save money over what I have. I paid a lot more for the pre-made but it was simple and quick and a known quantity.

    The other thing to think about with a setup like mine is that it is NOT rounded inside. I'm wondering if maybe cutting part of my extra brick material at an angle and placing a triangle along the side of the forge opposite the flame might create enough of a swirl to matter. Mine is a large enough chamber, with the actual flame far enough back, that it's not a really bad hotspot, but it could definitely be improved.

    I'd like to upgrade to a digital electric, but I'd have to run additional power to the garage/shop and the initial cost is a lot higher. I don't think I'd take as much pride in that method either. Even with my relatively simple work so far there's a certain extra something to this method over a kiln style oven. It just seems less personal to me. The option would be very nice for stainless though.
  9. smorgan345


    Mar 8, 2007

    I'm doing the same thing right now and was wondering some of the same questions. I am going to use the burner off of turkey fryer I have. i too want to heat treat with it so Im concerned about temperature control. I thought The same thing about using a brick to distribute the heat more evenly throughout the kiln but I wasn't sure if it would dissipate it too much and keep the kiln from reaching the necessary temperatures. knowing what the actual temp is inside is an issue as well. I looked at some electric kiln thermometers and even a wood burning stove thermometer that I thought might work. have u had any thoughts on that?
  10. jasonprom


    Dec 3, 2008
    I also couldn't find the JT-7 torch when making my first forge. I've had great luck with the Mag Torch MT-560 (http://www.magtorch.com/mapp560sub.htm). I've seen this at three local hardware stores including Northern Tool.

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