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Set up my first forge, forced air burner question


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First off- hello all!

Being a relative newbie to learning forging, thanks for sharing tons and tons of your valuable experience.

I found this site after I built my forge...of course. Smh.

I'm still pouring over several years of posts.

Please note that I'm an army veteran- and will gladly take criticism, humor, advice, and general ribbing fairly well if offered in genuine intent. Lol...


Having done months of research, I set out to build my forge.

I've built a cylindrical propane, two burner forced air setup.

I wanted a general, decent size-not too big or small.

It's a 12" dia. tank, 23" long with 2" of ceramic wool with hell's forge 3000 refractory.

My burners are 1-1/2" pipes with 2" flares at the ends capped with flat steel and pattern drilled gas holes.

These are fed from a 2" piped blower reduced to meet the 1-1/2". The blower is an older industrial squirrel cage style... putting out decent air.

Currently feeding from a small 20lb tank through a 0-30 psi guaged regulator... running between 3-5 psi (more or less) at full hot burn.

Ok, so I'm getting decent temps... not welding temperatures at first- due in part to a miscalculation in mixture tube length and my own stupidity. I've since fixed that, and I think I'm burning much better.


But, I'm getting a pretty decent howl or whine/whistle from my burners from time to time. Slight adjustment up or down on the fuel and or air tuning diffuses the whining.


I've used torches, and gas tanks for cutting heating metal most of my life, and have years of experience with natural gas and propane heating furnaces with much smaller scale burner systems- but...

Being a novice at burners on this scale...

Has anyone else ever run into this?

I would assume overpowering either air or fuel would eventually shut down the burners... much like a torch. But is the howling a worry for any other reason than it's irritatingly loud on the hearing?


As soon as I can figure out how to decently drop 4-5mb file size on my pictures, I'll try to post some.


Thanks, joel.

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Good Morning, Welsh

At the very bottom of this page, there is a listing of some of the Blacksmith Association in North Hamerica. Look for a group that is near you and then you can get some 'Real, Hands-On' Help. Yes the computor is nice, but there are other choices, close at hand.

It is better to start small, with a smaller one burner Forge. Start with a proven design, you are not the first to walk this rope. Every one of us has started, at some point.

Good Luck, Neil

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Good Morning,

Frosty has a proven, simple burner. There are plans right here.  Mike has tons of experience with Propane, even has a book on Forge Burners. All the material you think you need, ask before you buy it. The knowledge base here is HUGE!! Sometimes a little humour gets mixed in with a serious question, sometimes the humour takes it to a complete different place.

If you are starting with a 2 burner design, turn one burner off. Start simple, adjust air (I use a gate valve in the air flow), adjust propane regulator pressure, adjust Forge openings. Too many burners will make the propane bottle freeze sooner. Use 2 or 3 propane bottles is parallel to stop the freezing. Put the bottles in big buckets of water, so the water acts as a heat sink and the bottles won't freeze solid very fast. This is a problem with the draw of the propane gas from the surface area of the liquid, inside the bottle.

Stay safe, play hard, wear your safety gear. You don't get another chance at Eyes or Ears. Use the gray matter you were born with!!


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Welsh:  If I haven't welcomed you aboard already, welcome aboard, glad to have you. Thank you for serving!

Can you post a pic of your burner? I'm not clear on the design, especially the plate and holes part. Is that over the output end or what?

If the holy plates are over the burner outlets (nozzles) what was the reasoning in the plans you followed? Gun burners especially are easy to tune so "flame holders" are unnecessary for well built and tuned burners. 

Without a couple pics, NO VIDEOS! of it running all I can do is guess at the whistle, shriek, scream. Here's my educated guess . One burner that diameter is way more than necessary to bring that volume to welding temp. You have a piece of holy steel welded over the burner nozzle. 

So, what's probably happening is the flame from those oversized burners is moving too slowly and when the plate gets hot it starts pre-igniting burning back into the plate and sputtering. Lots of holes with a high speed stutter equals a high frequency sound. Squeeeeeeel

With a 1 1/2" nozzle diameter a single burner is more than enough to melt iron in probably a 3,000 cu/in forge. An old friend of mine used a single 1 1/4" (sidearm) naturally aspirated burner to do iron melts up to 20-25 lbs.

Did you follow a set of proven plans or base your build on something you saw in a Youtube video? You have to really be careful what you believe on the web and until you have enough knowledge of the subject to sift the wheat from the chaff. You run into all kinds of folk who sound like they know what they're talking but are pretty much out in left field somewhere.

I'm glad I reread your post before hitting the button! Save pictures to a file on your computer, posting directly from a phone is problematical. I resize pics on my computer by doing a save as at a smaller file size under a new name.Then select the "choose files" button at the bottom of the text window you're writing in. Browse to the folder with the picture you wish to send, select and a thumbnail will appear below the text window. click the + and it will be placed where the cursor is. I will make a couple free lines first so I can continue writing after the pic. Double click the picture and an edit window will appear. I resize by making the number smaller till it's a decent size.

What you need to know for the burner size is the "volume" in cubic inches. Telling me how long and wide the shell is isn't going to do a lot of good, I don't do that arithmetic for folks anymore. Sorry, nothing personal but it's pretty basic math, width x height x length in inches. Then figure one well tuned 3/4" burner, either naturally aspirated or bun (blown) will bring between 300-350 cubic inches to welding temp. The shape has an effect of course, long narrow will have a hot spot and temps will taper off with distance. Make sense?

A 1" burner is approx 1.78 x the area of a 3/4" but the output is a bit better than 2 x. A 1 1/2" burner is a bit better than 4x the area of a 3/4" burner and that works out to significantly more output in BTUs.

So, you have WAY too much burner. Lose the perforated plates and cut your forge size down to maybe 1/2. in practice you can't forge more than a few inches while it's still hot, 6 is a pretty much accepted max length. a 23" long forge isn't in the stadium as practical. Unless of course you have some specific use for something that long. 

The diameter isn't too oversized you'll be able to work odd shapes which is a good thing.

A last bit of advice. I try not to discourage folks from trying to help but you have to be aware a lot of them are as new as you are and don't know what they're talking about let alone understanding it. Some  relationships to the question are so tenuous as to be off the radar completely. Be kind but don't get sucked in. There are a number of guys on Iforge who are experts building and using gun burners. My forte are NA (Naturally Aspirated) burners but in a furnace (forge) application it's not hard to trouble shoot each other's stuff.

Frosty The Lucky.

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29 minutes ago, Frosty said:

A last bit of advice. I try not to discourage folks from trying to help but you have to be aware a lot of them are as new as you are and don't know what they're talking about let alone understanding it. Some  relationships to the question are so tenuous as to be off the radar completely. Be kind but don't get sucked in.

This is especially important, here, and in general too. Such as, the video link I posted to doesn't pertain directly to resonation in a blacksmiths forge, but generally to the scientific principles of standing wave generation in tubes that are transferring combustible gasses to a flame holder. It'll give a deeper understanding of the principles involved, but won't directly help one with burner noise in a forge.

One extraordinary resource on burner design is Ron Reil's website. Which has both general and incredibly specific information and plans for forges and burners.


Going to a single source like that can help keep the ignorance based "knowledge" at bay, but also introduces, in general, its own bias of comprehension, since most everyone in a niech thing like this has their own sub-principles they adhere to.

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Yes, Ron and I are old friends, we talked this to death in the '80s and went with two different burner types.  We do catch each other up if we discover something new though.  Have you read anything of his? 

Please, PLEASE don't post about things of which you have so little knowledge.  Your content so far is pretty convincing evidence you should be ASKING questions not answering them. You aren't helping anybody and keeping you at bay is tiresome.

 Frosty The Lucky.

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I've read all of it, yes, that was over a decade ago though.

It has been a long time since I've been active in a forge, so trying to help people with what I do, or used to, know, is a bit difficult. When I've read back over most everything I've posted here the past few weeks, I have become frustrated, because the conversion of my latent knowledge to words is getting all jumbled and it's all coming across as nonsense. Due to intense elaboration being required in some parts. Such as lighting the anthracite coal, the description I gave was what I did when I used it and it worked well for me, but my explanation of what I was trying to describe was very wanting.

Anyways, thanks for the check, Frosty, I hadn't realized how far my active knowledge and descriptive abilities had slipped.

Caleb Paul Ramsby

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You aught to try a near lethal blow to the head for messing up your ability to express yourself. That's my excuse, please don't copy it okay? I edit constantly, I've spent a couple days writing and rewriting my longer post and it's still not satisfactory in my eyes. 

I hope I didn't come across too harsh or like I dislike you. We don't know each other well enough for me to dislike you. 

If you'd like please feel free to bounce what you want to post off me first, I'd be honored to help you articulate if I can.  Not everything of course, just things you have questions about saying. Sometimes I don't know I'm saying something inappropriate or way off base but I have friends who point them out to me so I can apologize and or go sit in a corner. 

Friends Caleb? 

Frosty The Lucky.


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1 hour ago, Frosty said:

You aught to try a near lethal blow to the head for messing up your ability to express yourself.

Lol... we're gonna have to get down to time frames here if we're gonna talk about copying here. I blame mine on a couple near lethal explosions in iraq. Smh...

It took Caleb's post for what I think it was- a relatively different kinda thoughtful idea for a maybe cause.? And more importantly- a pretty cool phenomenon. 

I'll figure out the picture thing here soon, as you nailed it on the head- they're all on my phone which I'm currently typing this on. But....

My burners feed from a single pipe, with a drilled cap for a single nozzle. This splits to a t fitting, into two elbows into two six inch straights, then into reducer flares.

I tested the burners prior to installing in the forge, and I found that they weren't burning correctly. They were burning back into the mixture tube. I could literally light one, and the other end would ignite back through it. The mixture tubes and elbows would get hot. That was the reason for the "baffles". To push the flame out through, and off the burner tips. 

As you stated, this was advised by a friend and found in a few youtube videos... and my limited knowledge of furnace burner setups.


I'm thinking of dropping to a single burner like you said- and cutting the body shorter in length to reduce my interior area. Thinking of a hinged front door with a smaller opening as well.



What about a you tube link? Is that allowable for video?

Initial fitting and setup before lining.

And burning after.



Edited by Welshj
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28 minutes ago, Welshj said:

Lol... we're gonna have to get down to time frames here if we're gonna talk about copying here. I blame mine on a couple near lethal explosions in iraq. Smh...

I was almost killed by a great white . . . birch in 2009, nothing as cool as an explosion.

Yeah, flame tables and bars are really cool but they're special effects and have less to do with burner type flames than oh I don't know what. I'm not sure what parallel Caleb is seeing, I'm hoping we'll figure it out.

Flame holders work by slowing the flow but that isn't the problem with your burners. The flow isn't moving faster than the propane air mix's  rate of propagation, having it burn back and light the other outlet is a dead giveaway. 

Here's my suggestion. Remove the sections between the T and your forge. Replace them with 1" dia. pipe and use a 1" x 1 1/4" bell reducer for the sacrificial nozzle. I'd do some walking with a calculator and note pad in the plumbing supply to decide which was least expensive to convert from your main supply pipes to the smaller. Two bushing reducers to the final pipe size or maybe a bell reducer and smaller T, etc. I make working sketches on graph paper to help keep things straight. Believe me brother I need help keeping things straight!

I'm thinking if you shrink your proposed forge a little two, 1" burner nozzles will work nicely. That's plenty of burner nozzle for about 1,400 cu'in and you CAN push guns farther than NA burners so max heatable volume isn't written in stone.

Reducing the final burner diameter will increase the velocity, especially without the flame holders. NO perforated plates! 

That's my thoughts to correct the screaming and increase the forge temp.

WHOA:o a picture arrived while I'm typing!

Your flames are rich, too much fuel not enough air but that's an easy adjustment. The soft sound is another indicator. It doesn't change my opinion above. Thanks for making it such a short video.

Frosty The Lucky.


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(Laughing in "I hate tree trimming" voice) lol....

I'd tend to think of a birch as a way cooler cause... but prolly with the same results as my explosions. (Something about changing underwear?)

I can open up my air on the tubes, and lean out the flames easily- but that tends to start the whining condition.

I like the idea of 1" tubes. I was worried that I would over power the gas mix with too much velocity. But I will definately make that my next step. I should be able to locate a 1-1/4" to 1" t fitting without too much difficulty I'd think.... I'll find out.

I got a little forge time in yesterday- and let's just say... it didnt work out well. I cracked a 100ish (he says) yr old coal forge that belongs to my little brother. Ugh.


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2 hours ago, Welshj said:

(Laughing in "I hate tree trimming" voice) lol....

"Not as much as the trees," frosty responds in a knowing tone.

Nope, no change my shorts experience, I didn't change shorts or wipe my own butt for weeks. 10 days - 2 weeks in a drug induced coma and another 6(?) weeks before I sort of came to my senses. Became aware of where I was and started speaking in coherent sentences. 9/28/09 to 12/23/09 and home.  I remember some of my time in the hospital but details are furry. 

TV was good though, they had 24/7 court TV! I couldn't watch Deadliest Catch, I can still remember how terrifying masses of crabs were, the bailers were worst of all. 

That's what they meant by, "Clay Before Using," cast proud in the pan.  Cast iron doesn't do well with close temperature differentials, the clay evens the heat out over a wider area.  I have a cast iron rivet forge with a cracked pan too, got it that was and it still works.

Frosty The Lucky.

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1 hour ago, Irondragon Forge & Clay said:

That is the main reason those cast iron pans need to be lined with clay before building a fire. Not being critical but if someone reads this it may save them some trouble and we have been asked many times why clay the pan.

No. By all means... be critical!

If it saves someone else the embarrassment I now feel facing my brother... then it's worth every sentiment.

Entirely too well noted!:unsure: Smh....

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Yeah, friends Frosty, no worries. I'm autistic, that's my brain issue. Which for me means that I'm naturally communicating at either a 2% or 98% depth, both of which, in their own ways, can be extraordinarily problematic. Which requires constant vigilance from me to put that into a more moderate range that's socially acceptable.

I'm glad both of you guys survived your traumas! As I think we all know a bit too well, in our own different ways, that sometimes, life can be death.

What I was referencing via the video link, was that of the principles of resonation and the production of sound being universal. In the examples in the video they're intentional and being produced by a powered resonator, in the forge they're unintentional and being produced by nature. In both of them, the sound is being projected into the air via resonating flames.

The reason for the sound going away and coming back when you adjust your mixture is due to the flame front velocity. That is, the speed with which the flame can travel through a combustible mixture of gasses. Which is influenced by the fuel type, presence of dilution gasses such as nitrogen in the atmosphere, density of the mixture, temperature of the mixture and variance from the optimal ratio of gasses for complete combustion. Here's a chart from Marks' Mechanical Engineers Handbook that will illustrate the mixture issue.


C3H8 is propane. As we can see, it has a tight range of gas to air ratio, in which its flame velocity drops by 1/3 rapidly in either direction, either rich or lean. And we can instantly see why burning pure hydrogen is so dangerous, as well as why a hydrogen flame is so compact.

As Frosty pointed out, the resonation is being caused by the flames going back into the flame holders. That's because the air/fuel mixture is traveling at a lower velocity than that of the flame front. Thus, why your burner quiets down when you adjust the air/fuel ratio in either direction. Since by doing so, you're lowering the flame propagation velocity.

The resonation itself is caused by the flame "supercharging" the orifice. The orifice has a natural contraction inside of it, caused by the compressible gas flow through it, so that the effective diameter of gasses emitted by it looks like \_/ with the orifice being the top. Then that high velocity spray expands when it gets out. So, an orifice like this has a contraction/acceleration and then an expansion/deceleration as the gasses reach it, pass through it and leave it.

A flame burning back into it will "flop" back out, because the burning gasses are being heated, thus they are expanding, thus when it starts to enter the orifice, the flow through the orifice will accelerate due to the expanding gas, which in turn slightly lowers the pressure behind the orifice, which will increase the flow through the mixing tube to the orifice, thus, pushing the flame back out. This is a series of pressure waves. The pressure rise and fall inside the large diameter mixing tube will be very slight, but as it nears the nozzles, that rise and fall will be greater, at the nozzle it will be the greatest and quickest.

This can be observed in slow motion with a typical propane soldering torch or bunsen burner if it is put on a very low flow so that it goes "whop, whop, whop" as the flame dances on the nozzle.

If the orifices are large enough and the flow is slow enough, it can dance back a significant distance behind the orifice until the accelerating capacity of the flame and general modification to the flow rates at various points of the burner by said backtracking flame have done enough to push it out. But it will generally be doing this in a rhythm, sometimes very slow.

If, however, the air/gas mixture reaching the flame holder has a significant inertial energy, and the flame propagation velocity is only just higher than is the velocity of the gas mixture through the nozzles, then the resonation, the flame jumping into, then being pushed out of the nozzle, will be occurring at extremely high speed, so fast, the gas pressures behind it won't have much modulation at all. High speed resonation is high cycle rate is high pitch sound.

So, like Frosty said, the solution is to increase the velocity of the gas mixture through the orifices, that's generally calculated by the vena contracta of the particular orifice(s), which can vary a good bit, and the area of the orifices and the pressure of the gasses being pushed or pulled through them, in this case, pushed. The product of the gas velocity and effective port area gives the gas flow rate. All a fan does is generate a pressure differential, the size or blast area of the fan gives the potential flow capacity for a given pressure differential. That is, a large fan can be limited by a small nozzle and a large nozzle can be limited by a small fan.

In general, for maximizing resistance to flow through an orifice, a smaller orifice is better. The coefficient of friction of fluids in transit are increased in an exponential manner as to the reduction of the mean effective radius of the orifice, tube, pipe, etc. Thus, if you have two plates, one with many small holes and one with a few big ones, but they have the same effective gas passage area of say 1 square inch, the one with the big holes will be more likely to flashback and make whines and howls and such. This principle is why many production combustion devices have screens and/or a porous matrix behind the nozzle. They act as minute passage resistors that allow the flame to sit right inside of the orifice but not enter and rapidly spread in the mixing chamber or "flashback".

But really, just increase the flow velocity by decreasing the effective nozzle area by, as Frosty said, using smaller and/or fewer nozzles. As long as you've got a flow rate above 2 1/2 feet per second in the normal operation, there shouldn't be any issues. But too high of an orifice velocity at high burner outputs will push the flame so far away from the nozzle that it will become diluted and not be able to sustain combustion. Inside a forge that's less of an issue than in the open air though, due to everything being insanely hot inside of there.

In conditions where either flashback presented a tremendous danger or a more compact flame was required, one very old trick that was used was to use very high velocities through the nozzle, well higher than the flame propagation velocity would be, and use two nozzles, with their jets impacting each other at 90 degrees. That impact zone was then the origin of the combustion zone, and the turbulence generate from said impact, kept the flame from lifting off of the nozzle and it also violently blended the air/fuel so that it completed combustion very rapidly and compactly.

This effect can be witnessed with two standard propane soldering torches, holding them to make their flames strike each other at 90 deg.

Granted, that's not required for a forge or anything, I just found it fascinating and wanted to share it.

I'll shut up before I start going on about the issues surrounding the vaporization of liquid fuels for use in a gas burner, because that has nothing to do with this!

But I am just holding back about how cool(and potentially extremely annoying) a forge would be if a speaker were introduced to the mixing chamber in such a way that its resonation was transferred to the flame, making for a really "hot" boom box.

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A hot boom box... hmm... I love music. Every "shop" I've ever had has had sound.

Well, just for the heck of it... and working with what I had on hand- I pulled the burners, and configured it down to just one burner. I pulled the drilled baffle off the nozzle and tried it out.

With my blower- I couldnt even light the burner outside the forge without almost closing off my air. It kept blowing the flame right off the end.

Got it tweaked, burning consistently. 

Re-installed in the forge body and lit it up. Warming up the forge, and tweaking the mix til I got a suitable consistant  roaring fire. In a rich state- I could literally watch the flame roll around and out the body. My burner angle is a little off from before- but with a single burner... I'm getting almost a 20"? Flame from it. :o (on the bench test)

I could only get up to what I'd call a medium to high orange heat in a 3/8 rod. Less than what I had before.

So, on hold for now til I get the needed parts and a larger fuel tank. Sigh...

By the way- a huge thank you to all who posted advice! I much appreciate it, and will be considering it all and acting on much of it.

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Welsh: tune for neutral, it'll get hotter.

Caleb: I get it, thank you for sharing the confidence, the tone of your previous posts make sense now. 

That was one heck of a good post, I followed it well enough I think I can put it together with what I know now. I see the relevance of the flame table to Welsh's screaming burners and the problems. We were saying the same basic thing but from completely different perspectives. Too cool.

You and Mikey should have some good conversations, he has a much better formal understanding of burners than I do. 

Frosty The Lucky.

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I've always been known for being different in many things... especially perspective! That's really a pretty cool way to put it frosty.

And I tend to think that nail, hammer, head..... meet.

Because last night, as i think of it now.... a single burner- not one bit of whine or howl at any level.

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  • 1 month later...

So, a few updates since my last post... I picked up two 100 lb tanks for $120 locally. Great shape,  and only 2 or 3 yrs old. Much better, longer forging time!

I've dropped down to the 1" diameter tube frosty suggested with great results. I'm now well within the range of forge welding- just not within the skillset yet. I've tried, but chose a poor... combination of steel and shapes to attempt. But it was more for the experience of trying. (52100 bearing race, and spring steel.) 

Also forged a handle, and door hook hardware for the shed, as well as a couple blades.

Also got power run out to the shed, and some lighting arranged.

Waiting now on completion of my belt sander from a machinist friend who's building it for me. Got a sneak peek update picture the other day- right now, he's awaiting motor delivery due to the coronavirus mess... to get motor mount plates setup and aligned.





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