Monday, April 14, 2014

Charcoal Washtub Forge

A little description of the project: this is a charcoal burning forge designed for use in making knives of bowie size or smaller. It does not have a clean out drain or clinker-breaker like a coal or coke forge, and does not require the constant influx of air as a coke forge would. A simple hand crank blower is enough to provide air for this forge. The working area is approximately 14 inches long and 5 inches wide, allowing for the heat-treating of a complete knife below that length, or the blade only of a slightly larger piece.

The forge is made of simple parts that can be gathered cheaply (or in some cases, completely free), and assembled in an afternoon. The only time consuming part of the build will be allowing the adobe lining to dry before the first use of the forge.

The parts list for the forge is very small, and can be gathered or purchased fairly inexpensively. In some cases, you may know someone with acceptable substitutes that are willing to give them to you. 

  1. A frame to hold the forge lining: I used a 7.5 gallon Behrens Hot Dipped Galvanized Oval Tub from my local Ace Hardware. Their online reference is 024826203230.
  2. Hand crank blower: I purchased one from a seller on ebay, I believe he makes them himself. But you can easily find an old champion blower or the like for cheap.
  3. The tuyere is made from a piece of 1" ID black metal pipe. I bought a piece 24" long from my local hardware store, but you really only need to make sure you have enough length to fit through the tub or frame with the threads exposed on the outside.
  4. Fittings or reducers will be needed to connect the hand crank blower to the tuyere. I used a 2.5" - 1.5" reducer, a 1.5" - 1" reducer, and some threaded nipples to couple the reducers together. A couple of metal screw clamps and a dryer hose would work, as well.
  5. A 1" threaded cap will be needed for the end of the tuyere pipe, to act as a clean out and to keep air pressure inside.
  6. A stand to put the forge and blower on. You can make this yourself from lumber, or buy a portable work stand from the hardware store.

Once you have all your pieces, either following this design or using your own, you'll need to begin assembling the parts. I'll walk through the fabrication of my design, but the steps are universal for this type of forge.

Fabrication will start with the washtub, so that it can be set aside to dry (if painted) while you finish the rest. Mine had to be at a certain height because I used rigid pipe to connect the tuyere to the blower. Mark, on center, for the tuyere; it should pass through the tub length-wise. Use a hole saw to cut a hole for the black pipe. A pilot hole and a pair of tin snips can be used if you don't have a hole saw handy.

Slide the tuyere into place to make sure that it is centered and runs level through the tub. While you have it fitted, mark the tuyere pipe for the eventual air holes. From the inside of the tub, mark the tuyere pipe inward 2 inches. Make sure to do this on both sides, and then remove the tuyere. You can set it aside for a few moments.

Now we'll make the slots in the tub to allow you to insert and remove the work piece. From the top and center of the hole you made, mark a line 2 inches upwards and 5 inches wide. From the edge of this line go straight up to the top of the tub. Once marked, cut out the notch with a cut off wheel or tin snips.

With both notches made, be sure to clean up the holes and notches so you don't cut yourself on any sharp burrs. At this time you can paint it if you prefer (I did), using a black matte high temperature paint. Either way, set the tub aside so we can focus on the tuyere.

Between the two lines you marked previously, mark a straight line length-wise down the pipe. Every inch down this line, mark or pre-punch a guide hole. Don't go over the line, and stay as close as possible to it as you can. Don't worry if your last hole is a little inside the line and doesn't quite match up. Now drill the holes you marked with a 1/4" bit through only this side of the pipe.

Once the tub has dried (or not, as you prefer), you can assemble all the pieces. Attach the fittings to the blower, and the tuyere, and put it through the tub. If you want an added measure of safety, you can screw a mounting bracket to the tuyere and the bottom of the tub.

The last step once all the piping has been installed is to mix up some adobe* and make the forge body. This is personal preference, but I'll include a picture of my design. I made two raised platforms from the tuyere to the bottom of the notch, and 2 inches out. From there, I made walls even with the sides of the notch on both sides. This gave me the 14"x5" aprox work area.

Make sure to screw the end cap on the tuyere, and let the adobe dry out before adding your charcoal and lighting the forge.

* The original design for this forge mentioned an adobe recipe of 1/2 parts earthen clay, 1/2 parts sand, and a couple handfuls of ashes to help add refractory qualities. Mine ended up being closer to 1/3 clay, 1/3 sand, 1/3 dirt with many handfuls of ash. Look around and find a good recipe you feel comfortable with and experiment.

Lively, Tim. (2014, January.) Wash Tub Forge. Retrieved April 14, 2014, from
Kampman, Igor. (2013, April 3.) Tim Lively Inspired Washtub Forge. Retrieved April 14, 2014, from
metalhead0jtk. (2010, December 22.) Blacksmithing - Build a simple charcoal forge. Retrieved April 14, 2014, from