Part II: Building the Forge Body
With my burners done, tested, and working, I moved on to the fabricating the forge body. The body holds the burners and retains heat for efficient heating of metal work. It also holds a majority of the plumbing that routes propane from the tank to the burners.
Forge Body Preparation
The tank was covered in old red paint that was covered in gunk. So I used a stripping wheel on my angle grinder and stripped it down to bare metal.
I then found the center of the face and used a drafting compass to draw an arc that left a hair over 2″ of material around the opening (because I later put in 2 inches of insulation). I added the thickness of the firebrick to the 2″ to determine where to put the flat base of the opening.
Once it was laid out, I patiently used my angle grinder with a cutoff wheel to open it up. Slow and steady wins the race here.
Prep for Burner Mount Collars
With the main openings done, I moved onto the holes for the burner mount collars. The collars are made of 2″ diameter schedule 80 pipe, 3″ long that I was able to get from a good friend. I used the collars outer diameter to determine the size of hole saw I would need and then used the hole saw to cut the holes.
The holes are 15° off of top dead center, and for two important reasons. First is, when its cooling off, the heat doesn’t shoot straight up the burner tube and damage the brass accelerator assembly (the fuel only ignites in the nozzle during normal operation). Second, it helps create a swirling action inside the forge to help circulate the heat.
Making the Burner Mount Collars
The easiest way to get the screws 120° apart was to take a piece of graph paper and wrap it around the pipe. I then put a mark at every 1/3 of the way across it, wrapped it back around the pipe and transferred my lines. I measured about 3/4″ to an inch down from one end and drilled and tapped for set screws. Then, it was time to test fit it. I had to use a file to finesse the opening for a snug fit, better to have to remove material than add (its a bit easier to add material back when you’re working with metal than with wood).
Mounting the Burner Mount Collars
With the collars done and ready to weld, guess what I did next… I welded them to the body. I used a burner and placed it in the collar and let the end of the burner rest on the firebrick that had a 2×4 under it. This helps ensure that when I go to weld it, it is aligned so the burner will point toward the center of the forge.
Fabricating Proper Footing for the Forge Body
The original footing on the tank was a thin flat bar that was welded to one end on the bottom, not very stable, and would have the forge a little to close to the bench for comfort. So I got some 3/4″ square tubing and made some simple legs. I am glad I had the foresight (for once) to add the 1/4″ holes in the base of the legs for mounting — they came in quite handy when I build a cart for it.
These level out the forge and lift it up a bit. Keep in mind, the forge gets well over 1500°F on the inside, and about 300°F on the outside even with the special insulation. The base of the legs barely gets over 100°F after extended use which is a lot better considering it sits on a wooden cart.
Mounting Plate for the Gas Plumbing
Yet again, I didn’t take enough pictures while I was building it (sorry). I used more of the square tube and some 2″ wide steel plate for the mount. This holds the plumbing for the gas, but being about 3″ away from the main body, it (like the legs) barely gets over 100°F during sustained operation.
The plumbing was probably the single most expensive part of the build, I spent about $100 on brass fittings and couplings. I used refrigerator line to go from the manifold to the burners and for the idler circuit (where you see it loop back on itself). I mounted the assembly to the plate mount using 1/4″ U-bolts and used a piece of PEX pipe between the brass and the U-bolt to protect from wear.
I used a 0-30 PSI propane regulator for a turkey fryer, a basic regulator attached to your grill in your backyard barely runs at 1 PSI and the burners need at least 5 or so PSI to run without stalling (they work based on the venturi effect, the high-speed flow of the propane draws in the air surrounding the slots in the burner).
I procured the valves, glycerin-filled gauge, 0-30 PSI regulator, and 9′ quick disconnect propane hose on Amazon for much cheaper than the store (I saved about 50% on the valves compared to the big box store). I did get the female quick disconnect from the big box store – I got the ‘Industrial’ one since it has a rubber seal on the inside so I mitigate risks of fuel leaks.
Safety Note: TEST your plumbing with COMPRESSED AIR and soapy water around your joints and make sure there are no bubbles. If you have a leak with compressed air, no big deal. And use the gas rated Teflon tape on all the threaded joins.
Tools & Materials Used on the Forge Body
- Flux Core Welder – Flux core welders are one of the cheapest ways to get into welding. Note, this is not the one I have but this should do the trick for this job.
- Benchtop Vise – This is slightly different than mine but you can’t really beat it for the price and surely comes in handy.
- Tap and Die Set – Different than what I have but should be plenty for this project. Its a trusted brand and the price is right.
- DeWalt Angle Grinder – I used this extensively on this project as well as many others.
- Flap Disk for Angle Grinder – Great for powering through the poor welding jobs of mine to make it look nice and clean.
- Angle Grinder Corner-Edging Flap Disc – Same as the above but excels in the corners like where the mount collars meet the body.
- Angle Grinder Cut-off Wheels – I used this to cut open the main openings on the front and back.
- Angle Grinder Wire-Wheel – This removed the old finish on the body in the tight places
- Paint Stripper for Angle Grinder – This removes a bulk of the old finish in a hurry without really damaging the steel below.
- Gas Valves – These ball valves are slightly cheaper than the big box store and have worked well.
- Pressure Gauge – 0-60 PSI Pressure gauge so you know how much pressure is moving through the system.
- 0-30 PSI Propane Regulator – This thing works very well and allows for fine adjustment.
- (Book) Gas Burners for Forges, Furnaces, and Kilns – This book was invaluable to me through this process.