Gas Forge Build 5: Intial Burn

Here have inserted the burners and tightened the collar screws. The flare tips are sitting up in the insulation about 1".
I placed to hard firebricks inside the bottom of the forge. This will prevent the ceramic blanket from compressing under the weight of whatever steel may go in. It also will keep the borax off the bottom.

I expect to replace these bricks from time to time, so they are not cemented in place.
With this arrangement the gas supply hose can come to the front or go to the back. After some consideration I think the hose would be best coming off the back of the forge.

This will give you an idea of the initial position of the torch inside the adpater. The torch can be slid in and out to tune the burner.

Additional notes: Stuff some scraps of ceramic blanket in the collar around the burner tube. This will prevent heat from escaping and avoid the chimney effect where hot air is drawn into the burner.

Open up the door to let some fresh air in and start it up.

Using a hand-held propane torch I lit the burners and cranked up the gas. The initial burn is quite rich. The large yellow flame is indicative of unburnt fuel.

After a few minutes I shut it down. Yes, It gets very hot. I don't think I'll have any problem forge welding in there. Some tweaks to do on the fuel to air mixture, but satisfied with the build so far. Stay tuned here for updates on the fine tuning.

Other Things of Interest

If your burners are running rich you can shoot some additional air into the intake to improve the fuel-air mixture. Remember we need about 1:100 fuel to air and that's a lot of air. If a burner is running rich, the additional air will make it more efficient and save you on LPG. The correct ratio will also reduce the carbon monoxide (CO) output of the forge. CO is bad.

LPG vapour is relatively safe and needs the right amount of air to burn. Unlike gasoline where combustion is possible with a wide range of mixtures, LPG needs the ratio to be just right

CO Detector
It's highly recommended that you get a carbon monoxide detector for your shop if you are going to forge indoors. CO is colourless and odorless and poisonous. Outdoor forges are ventilated and CO buildup is normally not an issue.
Storage of Cylinders
Legally in my locale (may vary by juristiction) propane is not to be stored indoors.

As per the Propane Storage and Handling Code, no propane cylinders may be stored or used inside any structure unless specified in the code, and shall not be stored or installed under any fire escape, stairway, or ramp used as a means of egress form a building.

This means your tank needs to be outdoors.

Orientation of Cylinders
The normal 20 lb BBQ cylinder must be stored and used in the upright position. The vapour is meant to be in the top of the tank. If the tank is on its side, there is a risk of liquid coming out of the tank's pressure relief valve or the main valve. One drop of liquid will vapourize to 270 times its volume. When mixed with enough air, this can become an explosion hazard.

Vapourization Rate
In cold winter areas this may become a problem as the low temperatures may prevent the vapour from boiling off inside the tank. The rate of boiling is a function of the temperature and surface area where the liquid is exposed to the ambient temperature.

Hose Protection
If you are concerned about accidentally hitting your gas hose with a super hot piece of steel, you can make a leather wrap for the hose. Optionally, you can buy a stainless steel hose braid to cover the hose or use foil for that matter.



Tim White said...

Are you happy with this forge? I am preparing to build one like it and would like to know if i need to make any adjustments to your design. Thank you for sharing your valuable knowledge.
Tim in Kansas

DanCom said...

I am very happy with the forge. I am doing some forge welding of cable right now. Works great! I find that one burner is often enough. I shaped a piece of firebrick and set it inside the effectively shorten the chamber. Then use the front burner.


dan hargrove said...

Hey Dan - Quick question on the tank size. If I went with a 10 gal tank, would 2 burners still be sufficient? I'm getting ready to build this baby. Thanks!

DanCom said...

I'd think a 10 gallon tank with 2" of blanket would be fine. With the 5 gallon two burners is a bit overkill as far a heat goes. Having two burners is useful for evening out the heat.

Théophile Forestier said...

How long you burn with one tank of gas

D. Comeau said...

I haven't ran through a full tank at one time. The fuel consumption would be based on a bunch of factors. Most of the work I am doing with only one burner running. I'd say approximately 8 hours of single burner forging.

Anonymous said...


How do you adjust the mix for an efficient burn. Will i need to induce an air supply somehow?

This is a great design.


D. Comeau said...

The mixture is controller by the size of the inlet to the Venturi (in this case some 1.5" nipple) and the size of the orifice on the MIG contact tip. I found that a 0.035" contact tip works great with the 1.5" nipple and produces a nice blue flame. When fitted into the forge the mixture goes slightly rich which creates a low oxygen environment.

For more control, one option would be to go with a slightly smaller 0.025" orifice and create a plate that moves over the air intake so that air can be adjusted to match the fuel and get the ratio perfect for any application. Going to 25 thou orifice is not going to reduce the overall heat a lot, especially if you have a two burner design.


David Rozier said...

How long did the cement take to dry. I used the same stuff you did and I am having issues with it taking a long time to dry. When I try to heat cure the lining, it starts to spall. Apparently they moisture is turning to steam and blowing the surface of the cement off.

D. Comeau said...

Hi David,

I let mine sit for a few days in the shop before firing it the first time. The air is pretty dry here, so it could take longer depending on the environment there.

One option would be to apply the heat gun to it for a while until the mortar set. Then test fire for a short time.


Nicolas St-Onge said...

I am currently looking for ideas for building my forge and was thinking about doing a chamber form steel and covering the insides with mortar and firebrick. Would this concept be good enough?

D. Comeau said...

The soft firebrick (K2300 for example) is excellent insulation for a forge. Keep the openings only as large as required. No mortar necessary if the steel is holding the bricks in place. If you are going to using a lots of borax as flux you may want to put some sacrificial bricks in the bottom. Flux is really hard on forge materials and the soft bricks are fairly expensive.

Nicolas St-Onge said...

Ok but would ceramic wool be a better alternative? Talked to some guys that says it does a better job of keeping the heat inside the forge

D. Comeau said...

Ceramic wool comes in different densities, temperatures and thicknesses. 2 inches 8 lbs/ft2 wool will make an amazing forge. I would take 2" of wool over 2" of soft fire brick any day.

The benefits of ceramic wool is that not only is it an amazing insulator and it can be curved to conform to round surfaces. A forge that is a cylinder or ached shape radiates heat better towards the center.

A value in bricks is in initial build time and maintenance. It's pretty easy to swap bricks, whereas relining a forge with ceramic wool and refractory is quite a bit more work. Bricks do eventually crack especially if you start banging them with steel and tongs.

Either way will work well enough for forging and welding provided you have enough heat and keep the openings small and closed them off when heating the steel. Way more heat will escape through openings than through the walls with either insulation.

I went with wool as I have a round frame. Many popular commercially made forges use only bricks and steel. I've seen some heat treatment ovens that are using bricks that are wrapped with wool so using both is an option as well. I can't see any reason why you couldn't use a square frame with bricks and the forge interior is lined with wool and refractory. However you want to use them.


Lori said...


Thank you for all of the information. I have built two burners pretty much duplicating your design, though I couldn't find 1.5" intake, so I'm using 1.25" and a .023" mig tip. Hopefully this will provide a reasonable mixture. I have gotten both burners to light, but I'm having some difficulty in 'tuning them' and getting them to stay lit. Each has slightly different issues.

The first burner is pushing the flame out until it goes out. Imagine the base of the flame (blue part normally at the tip of the flare) starts moving away from the flare in a straight line until it reaches about 6" then the flame goes out.

The second burner will light, but when I turn up the flame makes a 'whup whup whup' sound then then goes out.

Any thoughts or tips would be greatly appreciated.

D. Comeau said...


It sounds like a loss of vacuum in the Venturi. I would loosen the flares and slide them up the burner. Start with one burner and slowly eek the flare out until the flame is sustained. Once you have that, lock it in place and set the second flare to match. If you are able to have them both running at the same time bravo!

If they cannot be run at the same time you may need to up the gas pressure. I have an adjustable regulator and it needs a fair amount of propane (~ 7 psi) to keep both burners going.

Let me know how it goes.


Lori said...

Thank you Dan, I will definitely try that. The regulator is currently set at about 10lbs. Maybe that is too much?


D. Comeau said...

10 psi should be fine.