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Linear forge burner plans


AxL

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Hi!

I'm new to this forum and trying to build myself a forge and a burner. Let me prefice this by saying I know I can buy burners online, but I want to build it myself. I'm not good on the terminology either, so forgive my ignorance, and please feel free to correct me when I get something wrong. I'm not going to forge with it (yet), it's just for heat treating steel.

 I can't find a good plan for a linear burner that doesn't include buying parts from a plumber supply shop. I live in Norway and we don't have a lot of stores with such supplies available (we're not big on DIY because of regulations preventing us from doing much ourselves). I do have access to a lathe and mill, and misc. tools and I can make pretty much anything if I need it. Also have access to pipes, steel stock and a fair amount of pipe reducers and such, used in the oil industry.

Does anyone have plans/schematics for a linear burner that has all the ratios between pipe diameter, flare sizes etc? I have added a simple sketch of the kind of burner I wanna build so there is no confusion (not sure linear burner is the correct term). It's the kind used by Alec Steele in his forge. 

Like I said, I can make anything if I just know the correct ratios. I found a reducer today that I thought might make a good top flare, and start from there. The reducer (see pictures) is a 2" to 1" reducer (ID), about 2.5" long. The inner walls are the same shape as the outer walls, and to me it looks like it could be the right shape to create the start of a venturi tube. 

My regulator has a max rating of 150 mbar/2.2 psi. I can get a new one if it turns out to be too low. 

Any and all help is greatly appreciated! 

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If you google "mikey burner" or look for the book "Gas Burners For Forges, Furnaces & Kilns by Michael K. Porter." you should be able to find some pretty comprehensive plans. Mike (author the book) hangs out here as well and will probably chime in later. Most plans involve plumbing parts/MIG welding tips but it is especially the ratios between burner tube/air intake surface area and size of the gas orifice that are important. If you are able to machine to size you should be good. I am no expert on burners but I have successfully built frosty, s T burner in 1/2 inch and 3/4 inch sizes. (you will find the plans in the stickies here on the forum) 

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I think Mike  linked somewhere, probably in the Burners 101 thread. (also in stickes). Which is a wealth of info in itself :) Mike is on the other side of the pool so it may take a while before he is online. Your design looks like the Reil EZ burner with MIG tip modification.  https://www.abana.org/ronreil/burner.gif and https://www.abana.org/ronreil/design1.shtml#Reil

 

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7 hours ago, AxL said:

 I can't find a good plan for a linear burner that doesn't include buying parts from a plumber supply shop. I live in Norway and we don't have a lot of stores with such supplies available (we're not big on DIY because of regulations preventing us from doing much ourselves). I do have access to a lathe and mill, and misc. tools and I can make pretty much anything if I need it. Also have access to pipes, steel stock and a fair amount of pipe reducers and such, used in the oil industry.

Very well; let's start with the stainless steel reducer fitting in your photos:

You may need to lay out three reasonably equidistant threaded holes near to the small end of of the fitting. I like to use stainless steel socket set screws to firmly hold the burner's mixing tube within the small end of the reducer,  (but these screws can be changed out later, so use whatever is convenient to begin with).

Mechanically joining the parts together has several advantages: First, it reduces the size of the inside diameter of the mixing tube in relation to the large end of the reducer fitting. In a fan blown burner the ratio of the fan blade to the inside diameter of the burner should be no more than 3:1, so to avoid dangerous back pressure at the reducer/fan assembly joint. But in a naturally aspirated linear burner  3:1 is the smallest acceptable ratio, and  4:1 is better. It is desirable to be able to separate the reducer from the mixing tube when assembling, and later in adjusting, the gas jet. Finally, being able to change out mixing tubes can allow a single burner to be reconfigured as different burner sizes later on, as you find desirable.

Note: You can help adjust ratios with the thickness of the mixing tube's wall, and by grinding the inside of the large opening in the reducer fitting to form a long inner taper, which works much better for air flow than a short inner bevel. by inserting a beveled spacer ring between the reducers small end and the mixing tube oversize reducers can be made to fit up properly with even smaller mixing tubes.

The mixing tube should be "seamless"; otherwise you may need to grind down the inner weld bead which is often found in cheapest pipe.

Steel tubing has better tolerances than are found in pipe.

The three screws (which are recommended in the reducer fitting) can be reduced to a singe screw, IF the mixing tube and reducer can be made to fit snugly together buy twisting (rotating) the two parts against each other. On the other hand, a really sloppy fit could require six screws.

The mixing tube's  end must be beveled at least sixty degrees on its inner wall, to facilitate air flow; this doesn't need to be done at the beginning of construction, but can be  lect as final improvements to bring a weaker burner up to full power.

As a general rule the length of your mixing tube should be nine times its inside diameter; ten diameters can be used to insure a smooth flame in hand held burners, and eight diameters can be used to shorten a flame, in case of limited available room for the flame path.

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Thanks Mikey, I really appreciate it! 

So if I understand you correctly, since the large end of the reducer is 2", the inner diameter of the tube i use should be 1/2" (for a 4:1 ratio)? And the length of the tube, by rule of thumb, should be 4.5"? I will likely turn the tube on a lathe to get the dimensions just right. 

I have different sizes of MIG tip available, in metric. 0.8mm (0.031") and 1.0mm (0.039") Not sure what it corresponds to in actual size. What would be you recommendation? I'm running approx. 2.2 psi/150mbar off my regulator.

I'll try to get started on the construction tomorrow and come back with pictures.

Thanks!

 

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I have already perfected 3/4" linear burners using 2" x 3/4" reducers (see the MIG tip upgrade on Ron Reil's burner pages). You don't always need to reach for theoretical limits in the parts, to achieve your goals. You just need to get close enough to provide the mixture flow needed to build a very hot burner.

However, if you don't want to weld or braze the mixing tube in place, you will be forced to change reducer fittings, or settle for a 1/2" burner. Welding the two parts together will require #309 welding rod. Brazing the reducer and mixing tube together will require stainless steel brazing flux and 50% or greater silver content filler alloy. Also, you will have to use a special flat washer to insure that the gas jet is trapped dead center in the the mixing tube, during mounting of the assembly and saddle fitting, or else use a wooden  handle with a 1/4" hole in one end (to hold the MIG tip centered), to do so.

Use the actual inside diameter of the pipe or tube you use; not the nominal call out size. Also, you would use the full length of the mixing tube, if it slides inside of the small end of a reducer fitting, but only the remaining distance beyond the small end of the fitting, if it is attached to it, instead of trapped within it.

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A 1/2" size burner would need a 0.8mm (0.031" orifice size), long MIG contact tip. A 3/4" burner size would need a 1.0mm (0.039" orifice size) long tip. However, use of schedule #80 1/8" gas pipe will improve gas flow between pipe and tip enough to make short contact tips acceptable.

Understand the the actual orifice size of a MIG contact tip is always several thousandths of an inch larger that the tips designated size, which only concerns the welding wire it is meant for use with.

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The mixing tube on linear burners

While threaded pipe reducers have been used extensively to build linear burners over the last thirty years, they were the choice of convenience. The first linear burners used butt-weld pipe reducers to achieve the best possible air flow. But, threaded reducers didn't require any welding or brazing skill, and where also cheaper. Unfortunately, because steel water pipe is being marginalized by copper and plastic tube, threaded steel reducers are also being used less often, and so they are overwhelmingly being supplied as crude imports. Butt-weld reducers are a lot more expensive then threaded ones, and so mild steel reducers are likely to cost as much as stainless steel reducers.

Usually, the mixing tube will end up sliding into the small opening of a butt-weld pipe reducer fitting, or screwing into a threaded reducer.  But welders and brazers attach them unto the end butt-weld pipe reducers, or any other cone shaped part. Most reducers have part of their inside that will run parallel to the outside of the mixing tube, at some point.

The inside of the tube end is beveled to maintain good gas/air mixture flow, and the tube is pushed as deeply into the small end of the reducer as it will go before a gap forms between tube wall and reducer opening; this is the point where the tubes eight diameters are measured from. If the tube is welded or brazed onto the reducer the eight diameters are measured from the point within the reducer, where its inside diameter matches that of the tube. When welding or brazing the mixing tube onto the reducer, you need to use a square to make sure the tube's end is completely square to the reducer's end. The two parts are held tightly together with a length of allthread, two nuts, and two flat washers. Be carefull to keep the inside surfaces inline, two end up with a smooth transition point in the joint.

Note: The size of the gas orifice is a function of of the mixing tube's inside diameter, and nothing else.

Flame nozzles

We various experts had agreed that a 12:1 expansion taper was best on a flared flame nozzle; this supposition is being sorely tested and battered today. Apparently, how much taper is right for a burner depends on the flow dynamics of that burner. I found these tapered nozzles to give weak performance on my burners, and replaced them with stepped nozzles eighteen years ago. Stainless steel was found to last much longer than mild steel nozzles; and #316 stainless lasts longer than #304 stainless.

The nozzle diameter should be approximately the equivalent of two schedule #40 pipe sizes. One pipe part is used as a spacer tube of about 1" long. The stainless steel nozzle can be made of the next larger #40 pipe size, or a nearly equivalent stainless steel tube with the right inside diameter chosen from a pipe chart. For a 3/4" burner that would mean a 1" or equivalent pipe or tube for the spacer ring, and a 1-1/4" stainless steel pipe.

A 1/2" burner would use a 3/4" schedule #40 pipe a or equivalent tube for the spacer ring, and a 1" stainless steel pipe for the nozzle.

Note that stainless steel pipe actually costs less than equivalent tubing from Onlinemetals.com. They are pleased to receive small orders, and will cut parts to size for a small fee.

How to determine length of the flame nozzle: These nozzle are designed to run back and forth over the mixing tube to help tune the burner. As a rule of thumb the amount of nozzle overhang past the end of the mixing tube will slightly exceed the inside diameter of the nozzle. To that distance add the width of the spacer ring and 1/4" for slop; the sum of these figures are the length of the flame nozzle.

In the past I have used a ring of equally spaced stainless steel socket setscrews to hold the nozzle in position, and even two rings of them if my parts were a sloppy fit. It is necessary to force the flame nozzle into perfect alignment with the mixing tube; otherwise the flame will be forced off center of the burner; this is a destabilizing factor; avoid it.

If your parts are good enough that twisting the slightly out of round flame nozzle on the slightly out of round mixing tube provides axial alignment, then as little as a single screw may all that is needed.

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The gas assembly and saddle

The gas pipe is one-half of a 6" long schedule #80 1/8" pipe nipple (McMaster Carr online catalog), so it's wall is thick enough to tap 1/4-27 or 1/4-28 machine screw thread inside the cut end, for a Tweco style MIG contact tip; this now becomes the burner's inline gas tube, with an inline gas jet, which is the only way to make a powerful homemade burner. The burner’s other end, which still has a 1/8" tapered pipe thread, ends up connecting to the fuel gas source.

Note: This design needs no drill press. A 3/8" hand drill is fine; or a 1/4"drill, with a step bit will work.

1/8" IPS (Iron Pipe Straight) thread (AKA lamp thread), dies for which can be had from eBay and other online sources, are then run as far down the outside of the gas pipe, from the cut end containing the MIG tip, as you need.

Note: if you live somewhere that doesn't provide these parts and materials, compromise by substituting whatever heavy wall tube has an inner diameter that can be handily threaded for whatever MIG contact tip you can find. Then run whatever external thread you can substitute for IPS, and simply stop short of the area at the end of the tube that contains the internal thread for the MIG tip.

A flat bar (width determined by size of reducer fitting, but make it wider than you think it needs), is bent into a "U" shaped bracket, which I call a saddle for reasons that will become clear; it should fit over the large opening of the reducer, without slop. Drill two small holes for machine screws, in each open end of the flat bar, and one hole in the center of this saddle; thread the center hole with a 1/8" IPS tap, and assemble the MIG tip, gas tube and saddle ("U" bracket), with its open ends facing the MIG tip.

Place the gas assembly, saddle down, on the reducer, and screw the gas tube into the reducer until its end is protruding out of fitting's  small hole. Choose whatever method you like to make a centering spacer, wood, tape, or drill a plug fitting; it really doesn't matter. What you now have is all the parts that need to line up, perfectly in line for drilling the four small screw holes; with any care used at all, this is now a slam dunk.

Because the gas tube has outside threading, you can also cut out aluminum plate with a hole saw, to make a choke plate, and thread it, to screw back and forth on the gas tube.

If your gas tube ends up with a loose fit in the saddle buy a lamp nut in the lamp area of you hardware store, to act as a locking nut.

So, why bother building this burner?

(1) There is no easier burner to construct, with dead center aiming.

(2) It is a powerful, and trouble free design.

(3) Its choke can be exactly positioned, or closed tight against chimney effects, with a flick of the finger.

(4) I think, that the burner's extra wide saddle forces incoming air to begin swirling sooner than would otherwise happen in the reducer fitting; I base this personal belief on observations of several other burner designs, which run hotter than I can otherwise account for.

 

 

 

Well, there you go. Let me no if you have questions or run into problems; we are all waiting to see photos of flames bursting for from your hot new burner; is it done yet? Is it done yet? :)

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Not done yet sadly! Have been busy, but as far as I can tell I have all the materials I need available. Can't wait!

 Thanks for taking the time Mikey, I'll try my best to follow your instructions to the letter. Hopefully I'll have some pictures next week:)

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  • 2 weeks later...

I did run into a sort of snag. The lathe in the machine shop was reserved for our apprentice taking a test all of last week, so I couldn't remove the piece he was working on from the lathe. But I will get started today, and hopefully have some pictures for you this week! 

I plan to turn a bolt on the lathe, to make it fit snug inside the reducer and then just drill out a 1/2" hole in it. Hopefully I can find a 1/2" broach to make it nice and smooth. Otherwise I'll hit it with some sandpaper. Updates to come!

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On 8/10/2017 at 8:44 PM, Mikey98118 said:

But in a naturally aspirated linear burner  3:1 is the smallest acceptable ratio, and  4:1 is better.

I figured 2" opening on the reducer -> 1/2" size tube for the 4:1 ratio. But I haven't even started on the hole yet, so I'll find a suitable drill bit. So the tube's length should then be 9 x 5/8" or about 5.625 inches? I'm gonna cut it long so I have some room to fail.

Thanks Mikey!

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Got the tube nearly done, just needs a hole through it. Hope to get that done tomorrow, feeling slightly under the weather today. 

I made a small shoulder in the small end of the reducer so the pipe will fit up to it and make it all straight and true.The fit of the OD of the pipe is pretty snug to the ID of the small end of the reducer. I plan to weld it at the end, but maybe it would be best to set it with set screws first. Time will tell... Stay tuned for updates.

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Three set screws allow you to force axial alignment, and to keep the two parts aligned, even if you chose to weld or braze these parts together, the screws will keep it aligned during welding; which otherwise will be likely to warp the parts out of alignment through contraction. The exception to the rule is an interference fit, which doesn't allow the parts to move from contraction.

File the screw ends smooth, to keep them from scratching part surfaces; gouges on part surfaces cause a lot of trouble.

When you look down through the end of the reducer's large opening, you don't want to see an internal ridge; so if you see one, bevel the part, to provide better flow dynamics.

Since you have access to a lathe, it would be a good idea to replace that external bevel on the reducer's large opening with an internal bevel, for better air flow.

BTW, good looking burner, thus far.

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How thick is the wall of your mixing tube? What. OD., and what I.D.? Remember that a stepped nozzle is built with a center ring in order to end up with enough increase between the mixing tube's inside diameter and the nozzle's inside diameter (approximately 1/4"). I have a hunch that you may notl need a ring.

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The tube isn't a tube yet, I have to drill out a center hole of 5/8" or the closest metric size as that's all we have available. As of now it's just a bolt. I've been away for a couple of days so haven't been working on it, hope to get the tube drilled out today. The OD of the tube is about 22 mm right now, I can machine it down further if necessary. I'll probably make the nozzle on a lathe as well.

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Update: Got the hole drilled. It's 15.5 mm, because that was the closest I could get to 5/8". I couldn't find a 16 mm, which would have been closer by a hair. Gonna put a bevel in the top of the tube so it's flush with the reducer. And put a bevel in the top of the reducer. The inside of the reducer has a glass blasted finish, should I polish that off?

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2 hours ago, AxL said:

Update: Got the hole drilled. It's 15.5 mm, because that was the closest I could get to 5/8". I couldn't find a 16 mm, which would have been closer by a hair. Gonna put a bevel in the top of the tube so it's flush with the reducer. And put a bevel in the top of the reducer. The inside of the reducer has a glass blasted finish, should I polish that off?

 

Generally,  a few thousandths of an inch oversized mixing tubes are better than undersized. But a few thousandths of an inch undersized is no big deal.

The difference between sand blasted and polished surfaces fall into the "no big deal" classification, too :)

But, beveling the inside ridge will make a positive difference.

What is the thickness of the mixing tube wall. I can't give you any help with building the flame nozzle without knowing that. inches or millimeters; it  doesn't matter which.

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13 hours ago, Mikey98118 said:

 

Generally,  a few thousandths of an inch oversized mixing tubes are better than undersized. But a few thousandths of an inch undersized is no big deal.

The difference between sand blasted and polished surfaces fall into the "no big deal" classification, too :)

But, beveling the inside ridge will make a positive difference.

What is the thickness of the mixing tube wall. I can't give you any help with building the flame nozzle without knowing that. inches or millimeters; it  doesn't matter which.

The thickness of the wall is 3.4 mm. OD is 22.3 mm and ID is 15.5 mm. 

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I thought it was a little on the thick side.

At minimum you don't need a ring to create a step in your flame nozzle. Just turn a straight cylinder about 2" long. Drill and tap three holes for three equally spaced stainless steel screws, set back about 1/2" away from one of its ends. I prefer socket set screws. What kind of screw you choose is a matter of personal preference; that they are stainless steel is necessary. It is also necessary to sand the end of each screw into a flat face. If the screws leave scratches on the mixing tube, you will have  a sorry mess in short order.

Once, the three holes are threaded, you must sand or file their inner surfaces, because stainless steel is bad about deforming during threading. Once the nozzle will run smoothly back and forth over the mixing tube again, chase the threads, because file work on the cylinder's inside face, is likely to deform the thread. Yes, you've guessed it; you now need to check, for additional deformation inside the cylinder wall. Work back and forth, until the screws run smoothly in their holes, and the flame nozzle runs smoothly back and forth on the mixing tube.

Spend the time to do this work just right. Otherwise any of the part surfaces can gall, and then life gets real ugly. Do all of these tasks to the best of your ability, and you can miss out on a very galling experience :)

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Update: I haven't been doing much with this project the last couple of days, been really busy! But I got the set screw holes in the reducer drilled and tapped today, so I hope to get the bevel in the tube made tomorrow, and weld the tube and reducer together. I'm thinking I might weld the saddle on to the reducer and then drill and tap the hole for the gas tube on the lathe, to get it dead center. It seems like a good idea on paper at least... 

 

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