How to Build a Gas Forge

Written by daniel r. mueller
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How to Build a Gas Forge
Hobby forges, used skilfully, can yield beautiful results. (forging image by bright from

The principle of a forge is to combine flame, fuel and directed airflow into a central hub, usable for heating metal items before the hammering process of blacksmithing. This small propane gas forge will give you the heat you need to do anything from bending wrought iron bars to hammering out medieval replicas, when combined with a suitable hammer and anvil set. Fortunately, the process of creating forge fire with propane gas is easier and cleaner than the wood and coal forges our ancestors were stuck using. Scaling up this forge, and adding a piped fuel network supplied by a larger tank, can make this more efficient for heavier duty use.

Skill level:

Things you need

  • Safety goggles
  • Welding gloves
  • Metal table
  • Drill, with metalworking bits
  • Hacksaw
  • Pop rivet gun & rivets
  • Needle nose pliers
  • Two-inch diameter air ducting, bent and of length to fit your fan and table set-up
  • Household fan
  • Standard bricks
  • Moist natural clay
  • Breeze blocks
  • Hammer and chisel
  • 6 Propane torches
  • Long wooden matches
  • Laser or infrared thermometer

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  1. 1

    Use your pencil and a ruler to mark a 3 inch by 3 inch hole for the airflow pipe to go through the metal table. Using your drill and a metal drill-bit, make a small pilot hole, then a larger hole to allow for the hacksaw blade to pass though easily on each corner of the square. Run the hacksaw blade though the hole, tighten the blade firmly to the handle and saw the square hole out. Saw end off the metal funnel, leaving enough material so that the duct pipe and funnel can be joined by drilling holes and pop riveting the pieces together. Use the pliers to ensure a snug fit. Do the same with the end of the duct pipe and fix it to the table. Position the fan and test for airflow: you should have a steady low-speed air current passing up though the table.

    How to Build a Gas Forge
    Propane gas forges are cleaner than this coal model. (forge et forgeron image by LAURENT VICENZOTTI from
  2. 2

    On your metal table, lay out a flat array of small bricks to make a solid base roughly 3 feet by 3 feet, leaving a hole over the hole in your table. Use your moist clay to bind the bricks together, it doesn't have to be perfect, it just has to stop the bricks from sliding around. With your breeze blocks line up two rows, with the holes facing outwards, leaving a gap the width of your smaller bricks, solid sides facing down so that you will have two rows of double-sided holes to work with. Build up a row of small bricks between the two breeze block rows, stacking the bricks high enough that the centre row is roughly flush with the breeze blocks while marking the locations of the inner row of holes on the brick with your pencil. Leave a hole in the middle of the inner row that lines up with the hole in the base and table.

    How to Build a Gas Forge
    An anvil and tool set for use with a forge. (forge business image by Sergey Goruppa from
  3. 3

    Take your hammer and chisel and break several of your smaller sized bricks into rectangular pieces of varying sizes, ranging from one quarter to one eighth the total size of the smaller brick. These brick shards are to be used as heat shims for positioning your propane torches. Remove the bricks you marked with the pencil and split them in half with the chisel. Remove enough material so that when the bricks are put back together there is a gap just large enough for the propane torch ends to move through easily. Place the marked bricks back in their locations, with the new gaps facing upwards and into the centre of the burn area.

  4. 4

    Using your brick shims and your moist clay, fill the breeze block holes you intend to use to support the torches. Remember that you want the torches to sit supported finger tight, but not so tight that you can't pull the whole torch out with a little effort. Leave a gap so that you can adjust the flow regulator on the torch with a gloved hand easily as you position the torches.

  5. 5

    Light the torches with your long matches, one at a time, at a low fuel output setting. Once you have the torches lit, you'll need to adjust the flames to give you the heat you need. Use your infrared or laser heat detector to check the temperature, and also use it to ensure that the propane tanks are not heating beyond their safe specifications; however, the brick shielding and damp clay should prevent overheating. Depending on your smithing style, you can adjust where the burn area is hottest by increasing fuel to that part of the flame. Most smiths prefer the centre of the flame to be hottest, while some prefer the back end of the flame to be hotter.

Tips and warnings

  • If you are having trouble reaching the temperatures you need, consider building up a brick hood for the burn area. The more you cover the burn area the higher the temp; just be sure not to overheat the propane tanks.
  • A standard fan aimed closely at the funnel should give you the air movement you need; however, consider further customisation if you feel you aren't getting enough.
  • If you can find longer torch end burners use them instead. It will give you more distance between the tank and the fire, which makes the whole device safer. Better still is a tank with hose set-up.
  • Wear goggles as well as a fireproof vest and heat restart gloves at all times during use.
  • Keep a fire extinguisher handy for use if the forge overheats for emergency shut off; shut off the forge using valves whenever possible to avoid gas leakage. Be ready to react quickly in the event of an emergency shut off, practice the procedure beforehand.
  • Metalworking is inherently dangerous, always have a shop assistant present during construction and use.

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