[TheForge] Question for Jerry Frost on the T-burner

[JERRY FROST]

Once you tune a T burner properly there is no reason to adjust the fuel air ratio, The flame burns at a nearly flat ratio from minimum to maximum stable psi.

What size burner mixing tube are you building? I designate them by mixing tube size and wrote the plans I published for a 3/4" burner. The length of the tube is an 8:1 ratio based on the dia. So, .75 x 8 = 6" The tube length should be 6" for a 3/4" burner. You can make it longer but not much.

The T should be 3/4" x 1" 3/4" being the drop and 1" being the run. A plumbing T fitting the Top of the T is the "Run" this would be the water supply run, the "Drop" is where a faucet or whatever connects into the run. If that's not clear, The vertical shaft of a capital T is the drop, the cross bar is he run. 

Assuming you have the brass fitting threaded into the top of the T so the mig tip is aimed straight down the center of the mixing tube you can look through the intake ports (Run) and the end of the mig tip (jet).

The throat of the mixing tube is where the very end is in the T. The farther the Jet is away from the throat the greater the ratio of air per propane is induced. The induction ratio if darn near flat so increasing or reducing propane psi has insignificant effect on the flame properties. A neutral flame at 8psig will be neutral at 16psig as it will at 5psig. IF you manage to make a T that will hold a stable flame at really low psig.

So, YES once you have tuned the burner it needs no other method of controlling air intake. Plans on the net that say it does are made by people who couldn't follow the directions. 

NO, do NOT put the jet in the mixing tube, it will not induce sufficient air and invariably results in a T burner that burns lean and requires choke plates on the intakes.

My 3/4" burners use a 0.035" mig contact tip. The departure point is trimmed to approx 1/2 way across the intake ports as seen looking through them. When I trim a tip I either file it in a way the teeth on a fine single cut file cuts away from the hole so as not to roll the edges and distort the orifice. I trim by small increments 1/16" max to start. 

When I've shortened the jet length I clean the orifice with a torch tip file, preferably from the threaded end out and do NOT over do it or these little files will distort the jet. You only want to deburr and smooth the orifice. Maintaining a smooth laminar flow from the jet is really important.

Trim and deburr the jet and test the burner. Test it in the forge, not a vise on the bench. The back pressure caused by burning in a forge chamber effects how well it induces combustion air so testing in a vise isn't going to burn the same in the forge.

Don't get silly with the flare, a bell reducer is pretty worthless as a flare. The reason for a flare is NOT as a flame holder as in other burners, it lowers the psi in the stream of the air fuel mix. While this does slow the velocity some, the real benefit is lowering the pressure and increasing the burner's induction so you can design it with a larger propane jet and still maintain a neutral flame.

I've found a 3/4" pipe "Thread Protector" screwed on the output end of the mixing tube makes an excellent "flare." The OD of the thread protector isn't so much larger than the OD of the mixing tube you have to make a huge burner port or try to screw it on the tube inside the forge. 

That's a basic rundown of building a T burner. If you'll link me to the plans you're following I'll let you know if they're a good set. I can link you to a more developed set than that I published in one of the ABANA magazines. Unfortunately I published those on Iforgeiron dot com and would run into copy right issues if I post the plans here. I don't know if I can post a link to the Burners 101 section of Iforge without running afowl of theforge.list  rules.

Do we have a new list mom? Can someone tell me if I can post links to other blacksmith sites here, please?

Frosty

----- Original Message -----
From: "Bruce" <freemab222 at gmail.com>
To: "Blacksmithing List Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Sunday, November 9, 2025 12:23:48 PM
Subject: [TheForge] Question for Jerry Frost on the T-burner

This came up on Reddit:
"In all the designs for the Frosty Tee Burner (which I am about to build
and experiment with) there neither seems to be any way to adjust the flame
short of shortening the mig jet. Is there already some magic in the ratio
of the openings of the tee relative to the pipe size that just makes the
flame correct without having to adjust the air? Or am I missing something?"

I've never worked with these burners so couldn't field the question.  I'll
post the answer if Frosty doesn't first.

Bruce
NJ