Knife Maker’s Forced Air Propane Fired Forge for heat treating and forging.

This manual covers the steps taken to build a small propane fired forge. The body is constructed from a Harbor Freight 5 Gal. air tank


Propane Knife Maker's Forge

The Finished Forge


We started with a 5 gallon air tank from Harbor Freight

HF Air Tank

5 Gal. Air Tank

Using a wire wheel on a mini grinder, we removed as much of the yellow paint as possible. Then using a cutting wheel on the mini grinder,w we carefully cut the end cap off the tank.

paint remved

The paint removed, ready to cut the end cap off

Once the end cap was removed, we layed out  6″ diameter circle and drilled 1/4″ holes around the perimeter of the circle. Then using a bimetal blade on our jigsaw we finished cutting out the interior circle.

holes drilled

Holes drilled to make cutting the circle easier


Once cut out, the edge of the circle was smoothed using a grinding disk on the mini grinder.


forge end cap completed

Completed end opening on the end of the forge body

Once the end cap opening was complete, we fabricated four small clips from 1″x1/8″ mild steel. Holes were drilled in these so that they could be used to fasten the end cap back on to the main body of the forge once the insulation had been installed.

installation of the end cap clips.

End Cap Clips

Then using the same method used to cut the opening in the end of the forge, we drilled a oblong hole for the entry of the 1-1/2″ burner nozzle. This nozzle needs to enter the forge at an angle pointing forward, so that the burner flame creates a swirling pattern giving more even heat distribution. (see diagram below) Four 1/4″ hole are tapped around the nozzle. These are used to anchor the 1″ burner tube once installed.


burner nozzle

Burner Nozzle Placement


Once the nozzle hole and tube hand been fit up the parts were taken to a local welding shop to be welded in place.

nozzle ready to be welded

Nozzle in place ready to be welded


After welding the nozzle and attaching the clips to secure the end cap it was time to install the 1″ thick ceramic fiber insulation. Be sure to wear a respirator when working with this material.


Installing Ceramic Fiber Insulation


Closed End Insulated

boady and end cap insulation

Main Body and Open End Cap Insulated


Finished Insulation

Finished Insulation


Once the insulation was installed, all opening were masked off and the exterior of the forge was painted with high temperature black paint.


Ready for Paint

After painting it was time to coat the ceramic insulation with a few coats of Satanite refractory. A layer of fire brick was also added as a floor to the forge.  First the insulation is sprayed with water and then a paste mixture of the Satanite is spread on the insulation using a putty knife. The refractory material was built up to about a 3/8″ thickness, allowing each 1/8″ inch coat to dry before adding another.

Satanite installation

Satanite installation

a few coats of satanite

After a Few Coats of Satanite

After the Satanite had dried, a thin coat of ITC-100 was applied to give the forge body even better heat holding characteristics.

itc coating

Finished Forge Body with ITC-100 coating


With the body of the forge complete, it was time to move on to constructing the forced air burner assembly kit that has been purchased from hightemptools. The forge body was mounted to a rolling cart purchased from Harbor Freight tools. The burner assembly was built in a vise using pipe wrenches and the joints were made up using Rectorseal Tru-Blu pipe thread sealant which is designed to be used with propane fuel lines.  Besides the kit from HTT you will need a 100 -150 CFM blower and a 2″ floor flange and a 2″x6″ nipple to mount the blower to as well as a propane hose, POL fitting and regulator (0-17psi).

burner kit

Forced Air Burner Kit From High Temp Tools


Forced Air Burner Assembly

A variable solid state speed control was purchased off of ebay to control the blower speed. This was mounted in a metal outlet box purchased at the local big box hardware store. Notice in the picture below that you existing 3/4 nozzle that originally held the pressure gage on the air tank make a perfect insertion point for the Aubers Instruments  thermo-well and high temperature thermocouple for monitoring the forge temperature using the Aubers digital PID controler shown below.

Burner assembly

Another View of Burner Assembly showing the propane tank, regulator, hose, speed control and thermocouple



PID , Thermocouple and well. The hose clamp controls the depth of insertion into the forge body










Manual Created By on October 4, 2015