Forge Burner by Jerry Frost from Alaska

First off are a few rules of thumb to consider:
How much burner is enough? Most smiths consider enough burner to be one that will bring their forge to welding heat. With decent flux this is in the high yellow. Most people buying a commercial naturally aspirated forge settle for less. A base rule of thumb is derived using a simple linear burner in an uninsulated forge lined with a hard refractory or a brick pile. This rule of thumb is one 3/4" burner for every 350 cu/in of volume. This is a good baseline to use regardless of the burner you build or buy. If you insulate or buy/build a higher efficiency burner you'll have a good margin of overkill. Overkill is good; you can always turn it down but you can't go beyond max.
This is often about as far as folk go but there are a number of other factors it doesn't hurt to consider.
What type of burner do you want? I'm not going to go into (blown) "gun burners" here. I have nothing at all against gun burners. I just don't use them so have little to say.
Of the "naturally aspirated" induction devices there are two that are suitable for heating furnaces:
The first type is the "Linear" induction device. Examples of these are the Bunsen burner, Aussie, Reil, etc. The air intake, primary (gas) jet and tube are in a line (linear arrangement). They can be identified by looking up the bore. Ignoring choke plates, etc. if you can look straight through them it's a linear. A purpose built commercial linear induction device has a max amplification ratio of around 19:1.
The other appropriate induction device is called a "Jet Ejector".
Examples of these are Fisher burners, Mongo, Porter generations 2-4, T Rex, etc. A jet ejector's air intakes are arranged at 90 degrees to the tube and jet. Looking up the bore you'll see the jet and it's mounting but can't see through it. A commercial Jet Ejector can induce up to 29:1.
How choosing the type of inducer you want to adapt for a furnace burner effects things like tolerances. A neutral burn, air propane ratio is 17.5:1. If you decide to build a linear you have to do a darned precise job of it, seeing as max induction for a commercial linear is 19:1. You just can't afford to lose much efficiency and still expect a good flame. If on the other hand, you decide to build a jet ejector, you can fall well short of the commercial 29:1 ratio and still have a super efficient homemade burner.
Another consideration is buy or build? Either is a perfectly valid choice depending on your situation and bent. If, like Mike Porter, Ron Reil and myself, to name but three, you enjoy building a piece of equipment as much as using it, you'll really enjoy building your entire smithy from the ground up. If on the other hand you're a "git er done" kind of guy and have the cash, buying is a fine way to go.
I simply can't afford to spend several hundred bucks just for a hot fire. I built my own forge and burners. Not counting time invested I've probably spent under $100 over the last 15 years or so on forges and burners. The little forge I've been using since 95' will melt steel if I turn it up a bit, say 12-13psi.
Ron and Mike have both taken burner making to a high point. They make burners that are precision intense and time consuming. Both make burners that are several percent more efficient than the one I'm going to show you here. This is where Mike, Ron and I differ, I'm basically a minimalist at heart. I like my machinery as simple as will do the job well, I don't need perfection. I also seldom build multipurpose equipment unless it's a natural marriage. A good example is a forge convertible to a melting furnace. This is a good multipurpose device if you're needs are similar enough for the compromise.
The last "T" jet burner I built was summer before last and I spent a whopping $9.00 for parts and almost 20 minutes making it. The following description has been altered to reflect how I made my last burner.
(Yep, you guessed it, I have most of this text saved and update it as necessary.)
So, the attached drawing is of the Jet ejector type burner I've been using for the last 10 years or so. I call it the "T" Jet burner and with small refinements I haven't changed the design in 10 years. You'll quickly notice there're no labels, dimensions or other helpful tips. This is why I call it a "concept drawing" if you need more, let me know and I'll do what I can to help. Same for my description, I've tried to do an adequate job of it but some folk need more info. Just let me know.
You will have to spend a little time wandering around a halfway decent plumbing supply for the brass fitting to make up the mig tip and the lamp rod. You'll also have to find lamp rod. Hope you're not overwhelmed yet!
The tube is 1" x 8" black iron pipe.
The "T" is a 1" x 1" x 1" black iron "T".
The "jet" is a 0.045" Miller mig tip. Shortened to 9/16" long and deburred.
The jet attaches to the 1/8" SPT (Straight Pipe Thread) lamp rod via a 1/8"FPT brass fitting or cap drilled and tapped 1/4"-28. Get lamp rod at Fred Meyer's, etc. in the lamp repair section, get one or two lock nuts too. If you go to an electrical supply or hardware store, it'll cost twice or more as at dept store. On the other hand it's only a buck or two per foot at most, anyway.
You can eyeball center when drilling the top of the "T" for the lamp rod but the better the alignment of the jet down the center of the tube the better it will work. This alignment is the single most important factor to making a good tunable burner. Screw the tube and "T" together. Make match marks and chuck it up in the lathe to drill and tap for best alignment. After drilling the hole, chuck the 1/8" TPT tap in the tailstock or drill press chuck and hand crank to tap the threads.
This will keep them as perfectly aligned as possible. If you don't have access to a lathe you can use a drill press but will need to make a vertical "V" block to align the tube and all the rest.
Use a piece of large 1/4" x 2"+ angle iron as the base plate and weld two smaller pieces, say 1" angle parallel and square to the base. The idea is to clamp the vertical "V" block to the edge of the drill table with the parallel "V" hanging over the edge. The "V" needs to be as perfectly aligned to the drill press chuck as possible. Chuck up a long straight piece of round stock, say 1/4" and with the burner tube clamped in the "V" block align the 1/4" straight down the tube. Clamp it solid and you're ready to go.
I don't have a 1/8" SPT tap so I use 1/8" TPT (Tapered Pipe Thread. I can't recall what it's properly called right now) and thread the hole a little at a time till the lamp rod just threads through it. If you run the tapered pipe tap too far you get a lot of slop, you get a little anyway but it's controllable if you're careful. A little slop is actually helpful for fine tuning the jet's alignment.
Now thread the lamp rod into the "T" without removing the assembly from the lathe or "V" block and lock it in position with one of the nuts. Install the brass 1/8" FPT fitting on the tube and snug it up. Drill and tap the brass fitting for 1/4"-28. Now screw in the shortened mig tip, insert a 0.045 drill bit shank in as an indicator and spin the lathe to see if it's straight, gently tap the mig tip as needed till the tip is straight.
If you're using a drill press, remove the lamp rod and gently chuck it in the drill press. Insert the 0.045" drill bit shank into the mig tip and hand crank the drill press. Watch for any wobble and correct it with gentle taps of a hammer. Be careful or you'll damage the lamp rod threads.
Once you have the lamp rod and mig tip aligned thread it into the hole in the top of the "T" from inside. Bring the brass fitting all the way to the "T" and lock it down with a nut from the outside. Using pipe tape or Teflon paste, attach your hose fitting and you're ready to test fire it.
I wouldn't really call these a "project" they take me maybe 15 minutes to make with my lathe, 20 if I don't turn it on and hand crank it.
I also don't put tapered flares on them, I only run them in the forge and they work just fine. To be fair, they will not burn open air. If you have use for an open air torch then adding the flare and doing the trial and error work to tune it will be worth the effort.
A proper flare is a 1:12 ratio or a 2.5-degree taper.

Frosty

T Jet Burner