Air Tank Forge

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Several years ago somebody sent me pictures of a forge that they built using a portable air tank for the forge body.  I thought that this was a great idea at the time, but when I got to shopping around for a new air tank back then the prices were around $60.00 which seemed high.  I came across a 5 Gallon Air Tank at Tractor Supply the other day for $24.99.  So now that the price of them has come down, I decided that I would do a tutorial for building one.  The item number of the air tank at Tractor Supply is
SKU #122581799.  The some nice things about this tank are it already has a leg welded on it and it is light weight.  I have looked at stores and online and Tractor Supply is the cheapest price on the air tank that I have found.  This forge was built using two inches of 1" thick Superwool HT lining which will give you a forge that is 5 inches in diameter and 12 inches long inside.  This gives you 236 cubic inches of forge interior.

I know that there are 7, 10, and 11 gallon air tanks out there for sale as well.  You could use the same build methods for these size tanks with two or three burners.  Just make sure that you use the following rules in the build.  No more than 350 cubic inches of interior space for each 3/4 inch burner and you need to have your burners 3.5" to 4" center to center so you will not have uneven heating of your metal.

The air tank out of the box

Once I got the air fittings removed from the tank I used some WD-40 and a scraper to remove all of the decals.  Let the WD-40 soak in a little bit and the decals will come right off with the scraper.

I used a 4 1/2" right angle grinder with a 1/16" cut-off wheel to cut the front of the air tank off.

You will need to make a hole in the forge body for the burner holder by using a 2" hole saw in a cordless drill.  Be careful when drilling the hole, because you are not drilling a flat surface and the hole saw will want to grab when it starts to come through the steel.


This time I am using a Cast Iron pipe bushing for a port opening in the rear of the forge.  You can use either a  2" x 2 1/2" Cast Iron Pipe bushing and (1) 2 1/2" conduit lock ring or 2 1/2" x 3" cast iron pipe bushing and (1) 3" conduit lock ring.   For this build I am going with the 2" x 2 1/2" Cast Iron Pipe bushing and (1) 2 1/2" conduit lock ring this will give you a 2" opening in the back of the forge.  I used a 3" hole saw to drill the opening in the air tank.  If you decide to go with the 2 1/2" x 3" cast iron pipe bushing and (1) 3" conduit lock ring this will give you a 2 1/2" opening in the back.  You can always put a piece a scrap Superwool in the port when not in use.  I am not sure of the longevity of the cast iron fittings but there are several commercially built forges on the market that use them so I figured that I would give them a try.


The pictures above show the Superwool cut for the back end of the forge and the forge lined with two layers of 1" Superwool installed.

The firebricks were cut to a size of 3.5" x 6" using a 4.5" angle grinder with a cut off wheel.  This is a picture of the forge with the firebricks installed and the Superwool coated with Plistix 900F coating.  I let the forge sit for 24 hours after coating it with the Plistix 900F and then I slowly cured it using a Propane torch.

I used scrap Superwool to close up the opening around the burner tube and the burner holder.  This will help protect the burner and stops all of the heat from escaping around it.

Here is the forge burning at 8 PSI and using two bricks for the front of the forge.

The pictures above show a couple of different options that you can use for the front of the forge opening using the 2 1/2" x 9" x 4 1/2" soft firebricks in different configurations.

Build Note:  I had to weld a 1/16 inch shim to the bottom of the backside of the forge so the front of the forge would be level and square with the firebricks that I am using to help close off the front.  I am not sure if all air tanks are like this or not.


Forge Parts List:

(1) 5 gallon air tank (Tractor Supply SKU #122581799 )
(3) 1/4-20 x 3/4" NC hex head caps screws  ( 3 for the burner holder )
(3) 1/4" lock nuts
(1) 1 1/2" x 4" schedule 40 black pipe nipple
(2) 1 1/2" conduit lock rings
( 4 running feet) 1"  8# density 2372F Superwool HT 24" wide
(1) 3/4" Side arm burner or (1) Z Burner
(2) 9" x 4 1/2" x 1/2"  3000F heavy duty fire bricks ( for the forge floor ) Cut to 6" x 3.5" size
(5) 2 1/2" x 9" x 4 1/2"  2300F insulated firebricks ( to make the front of the forge)
(2 Pounds) Plistix 900F
(1) 2" x 2 1/2" Cast Iron Pipe bushing and (1) 2 1/2" conduit lock ring or 2 1/2" x 3" cast iron pipe bushing and (1) 3" conduit lock ring. (to make the rear port opening )

Below is a list of parts that you will need to get from the propane tank to the burner gas inlet. (Note: all of the following parts listed below are contained in the single burner connection kit. )

(1) 1/4" MPT x full flow  Hard Nose POL 7/8 hex
(1) 1/4" X 1/4" FPT 3-35 lb Propane Regulator
(1) 0 - 30 PSI Gauge bottom connect with 1/4" mpt
(1) propane hose with 1/4" male pipe threads on both ends
(1) 1/4" N.P.T. ball valve
(1) 1/4" x 1/8" threaded black iron pipe bushing

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Copyright 2017 Larry Zoeller 

Last Revision 09/02/17