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Fog horn Forge.

Paul McC

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Hi there,

I new to the hobby and just made myself a coffee can style mini forge to do some heat treating with.

However, when I lit it to see how it would go, I was confronted with a rather obnoxious fog horn like humming.

I have attached a video (if it loads properly) that shows the forge and the sound. The video muffles it a bit, but it is a rather intense noise.

Could someone please help me to figure out what I have done wrong.

The forge is a closed back type, I wondered if that might be the cause but I have seen a few videos online that were closed backed and seemed to work fine.

And I didn't want to cut a hole in it if I didn't have to. I wasn't sure if it would be more effective this way or not.


Whether or not it is relevant, I made it with a mix of vermiculite, perlite, sand and cement. 2/2/2/1 ratio. With the option of coating it with a layer 

of refractory cement if I need to.

It is 12inch long 8 inch wide with a internal hole of 10 inch by 3.5 inch. And its run with a basic map/propane canister burner.


I would appreciate any advice anyone could give me to address the issue I am having, Thank you.


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The sound is from the extra air being pulled into the forge through that little hole.  You need a larger hole for the torch flame to enter and the then the noise will just be a low whoosh.



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OK thank you.

Just to clarify,  a tighter seal around the torch inlet is not a good thing, having a larger hole will stop that noise plus allow more airflow into the forge?


Also, the torch I'm using came with this attachment (seen in pictures) would it be worth chiselling out a slot to insert that for the burner

Or would i not get enough benefit for the work it would take to put it in with the size forge that I have?


Thank you for your help.



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2 hours ago, Paul McC said:

Just to clarify,  a tighter seal around the torch inlet is not a good thing, having a larger hole will stop that noise plus allow more airflow into the forge?



Yes.  The hole should be at least an inch or 1.25 inches in diameter. This will also increase oxidation, which translates to more scale on the blade you're heating, but at HT temps it shouldn't be too bad.  Plus you can and should get some anti-scale compound.


That other tip is a flame spreader, and those typically run cooler than the pencil tip.  While it looks like a ribbon burner, it isn't.


To really increase the performance of a little MAPP forge like that, ditch the homemade refractories.  A square foot of Kaowool is cheap, and works MUCH better since it isn't a heat sink.  Of course, once you do that, you'll start thinking about a larger burner, and eventually you'll think about forging, and next thing you know you've built a real forge with a blown ribbon burner...  :lol:

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On 6/7/2022 at 1:17 PM, Alan Longmire said:

To really increase the performance of a little MAPP forge like that, ditch the homemade refractories.  A square foot of Kaowool is cheap, and works MUCH better since it isn't a heat sink.  Of course, once you do that, you'll start thinking about a larger burner, and eventually you'll think about forging, and next thing you know you've built a real forge with a blown ribbon burner...  :lol:

The slippery slippery slope, lol. 

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Guy Thomas

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  • 2 weeks later...

Thank you very much for your earlier advice, it was very helpful in rectifying the noise issue I was having.

However, it was then apparent that I had another issue, that being, that my burner option was wholly insufficient. 

Because I made my coffee can style forge about twice the size of most people's coffee can forges, my burner is to underpowered for it.


So I had to purchase an more standard option for my burner. (Shown in picture)

Though the question I have about it is, do I have to run it with the larger flared fitting on the end, or can I remove it and run it with the inch or so size 

stainless tube that is inserted in the end of the cast iron body of the main tube?


I have noticed that almost all videos and pictures I have seen of people using these types of burners have some sort of similar larger fitting on the end 

that goes into the forge to increase the surface area of the flame produced (I'm only assuming that is why it's on there)

However, I believe that it will be to large for the size of forge I have and that the size that the main tube is should be more than sufficient. 

Will I be OK to use it without that fitting or is their some reason that I am not aware of that requires an extra flared size at the end?


And to your earlier comment, even though I have had to get a larger burner and that I would love to be able to hammer some metal for real, (I would have built myself a forge 2 years ago otherwise) I unfortunately have a disability that has limited the functionality of my hands by 80%, so I am stuck with only the option of stock removal and using a forge to heat treat as I can only swing a hammer for a moment before I can't any more.

I envy you all because I love the whole aspect of taking a chuck of rubbish (or brought stock) and turning it into a functional tool or other that would be useful and In service for many years to come.

But, although I can't dive as deep into the craft as I would like to, I will sink my teeth into anything I can, and I am extremely grateful for the advice that you are all willing and openly sharing. 


Thank you very much.

s-l400 (1).jpg

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You don't need the thingy on the end unless you're trying to run it outside the forge. It acts as a flame holder by creating turbulence at the step-up, and the lining of your forge will do that. That style of burner does need a tight fitting hole, though.  They're usually slid into a pipe welded to the side of the forge.

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  • 1 month later...

Hi again everyone.
i had to wait for my new burner to arrive and then it took a little while before i was able to take the time to set it up and try running it.
but after trying to run the burner, it was not working as i was expecting it to and was wondering if you may be able to advise me agan on what i am missing.

in the video you will see that it is not working like a forge burner that i have seen in videos of others online,
its more like just a very large normal flame not like a torch flame as i was expecting.

in the video you will see the change in the flames intensity but not its form.
i start but closing the choke up which reduces the flame, them i open the choke up more which makes the flame larger.
then i do the same with the ball valve, i turn to reduce the flow which just reduces the size of the flame and the i open the valve up more which make the flame larger again.
which then i just shut the valve off as i didnt want to mess around with any of it for any longer than i needed to when i obviously didnt know what i was doing.

i have a 30psi regulator on my gas bottle, but i dont have a gauge. i believe i had the regulator turned on about half way, but i dont know if a regulator like that has a constant pressure regardless of how much you turn the knob or if it varys the pressure by how much your turn the knob.

also the hole in the side of the forge that the burner slots into if a close fit but it is not like a friction fit. it has mabey a mm or two of play in the hole.
in chance that it answers a question before it is asked

i would appreciate any advice anyone can offer.
also im sorry about the angle i took the video at. if it is necessary i can take another video to make it clearer to show things operating.

thanks for your time.

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I'm not the Venturi guy, but I se a couple of things.

First, you don't have enough air.  This could mean several things.  It could be that you don't have your regulator turned up enough.  A venturi works by the amount and speed of the gas flow.  If the gas flow is not fast enough then it won't pull in enough air to make the system work well.  If you bought one of the 0 - 30 psi regulators (often called Red Tops, because of the red handle on it) try fiddling the knob.  If you get a better flame by turning the pressure up, there's your answer.

It may also be that your forge body is too small and it's restricting the flow through it.  If the back end is closed, that could be an issue.  Open a port in the back end of the forge and see if that doesn't help.


As proof of concept, build a box out of brick (it doesn't even need to be fire brick) bigger than your can forge and is open on both ends.  Stick your burner in the side and light it.  If it burns better, the air flow through your can is the likely culprit.


How big (diameter) is your burner? 


Hopefully, one of the real venturi gurus will chime in, but at least I've given some ideas.



"The worst day smithing is better than the best day working for someone else."


I said that.


If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton


So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.


Grant Sarver

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Geoff is correct, you need to induce more air.  I would certainly start by opening up the air gate as wide as possible.  Air gets induced into the mixing chamber by the high velocity gas exiting the orifice in the center of the gas outlet at the bell opening of the burner.  If your gas pressure is low you may not be able to induce enough air.  Once your burner is lit I would gradually open up the gas at the regulator.  Actually the burner manufacturer should have given you instructions on properly lighting the burner and tuning it.  You can also run afoul of the safety stop that is now built into new propane tanks (to avoid having them run wild if the main valve is opened without a downstream regulator).


Barring direct tuning info from the manufacturer I would follow this procedure (note: this works for me, but proceed at your own risk):

  1. Close the main valve on your propane tank and dump any remaining gas in your downstream lines (open needle valve and regulator full  - stem full up on needle valve and full down on regulator).
  2.  Detach the regulator from the tank.  Confirm tank still has some propane in it.
  3.  Reattach regulator to tank (take care not to cross thread the valve and remember the thread is typically "backwards").  Note: these first three steps are to reset the safety, and not necessary for typical startup
  4. Close both the regulator and needle valve.
  5.  Open the main gas valve on the tank full
  6. Open the air inlet all the way (integral gate fully opened up to the stop)
  7. Put a wad of lit newsprint into your forge
  8. Slowly open the regulator about 1/2 way (crank stem down)
  9. Slowly open needle valve, the forge should light.
  10. Continue to open the needle valve until the flame begins to roar and turn blue.  Louder sound usually equates to a stronger flame.
  11. Once the flame is stable and blue at the end of the burner inside the forge, wait till the forge warms up to a good orange.
  12. You can increase the flame output, first by opening the needle valve full, then by opening the regulator further.
  13. If you want to adjust the forge atmosphere to make it more reducing (good to avoid excess oxidation on the steel surface and excessive scale) you can close down the air gate, slowly, until there is about 2-3" of flame starting to lick out of the front door.  This will be noticeably different from the  slow flame you have now.  You will typically need to adjust the atmosphere with this gate slightly at each different regulator setting and/or forge interior temperature.
  14. To shut down: close main valve first to let all gas burn out of lines. Then close regulator and needle valve (important to at least close the regulator to avoid having the safety stop engage again). 

Good luck and be safe.

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Just a note- make sure your regulator is rated at psi, and not inches or water columns.


Some may be bars as well.


All are differing measurements of pressure, and some are much lower pressure than psi increments.


Open the choke on your burner as well- that brass disc on top of the burner... it controls how much air your burner draws in.


In your video, it looks pretty well closed- but that may just be the angle.

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Thank you very much for the thorough instructions for operating a venturi burner.

Unfortunately my burner did not come with instructions.


You were correct in your assumption that I had the gate/choke mostly closed.

To be honest, I had no idea what I was doing and where to start which I guess was a rather dangerous thing to do.

I mostly fired it up so that I could get an understanding of what I don't know so that I had a point of reference to work from going forward.


I will give it another attempt this afternoon working from the instructions given and I'll leave an update how I went if not come back for more advice.



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God Dammit!!
is it just because im a noob at this stuff or does the universe want to test me at every possible juncture. 

thanks to the detailed explanation earlier of how to run the burner i was able to get a more satisfactory type of flame out of it this time
but now i have another issue that i would not have expected or be able to rectify on my own without so experience behind me.

the burner started out ok, although rather intense for my little forge. but then after a few moments it started to "pulse".
I cant quite think of a better was to describe it at the moment.
again, i didnt want to mess with this any more than i had to because this behaviour freaked me out a bit thinking it could back fire or something on me.

also, you will see in the video that the flames from the burner are surging out quite vigorously and i was wonder if that is because the burner is to larger for my little paint can forge, or is that something i can get under control with a bit of tuning? 
i havnt opened up the back of my forge yet, i wanted to save that as a last resort option only if i have to, but i am more than willing to if it is needed.

initially i just planned to slap together this forge so i could heat treat two or three purpose made knives i shaped for a particular project.
but the more i get into trying to set this up properly, the more im intrigued in the idea of investing in a larger forge so i can smelt some copper and brass.
but in the mean time, i think i need to cut my teeth on getting this smaller forge running properly and get a little bit of knowledge in the bank before i go down that road.

thanks again for all the help.

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6 hours ago, Paul McC said:

is it just because im a noob at this stuff or does the universe want to test me at every possible juncture. 

Yep, that is pretty much how it works :)  At least until the next noob comes along and distracts the evil spirits.  Somehow, magically, just as that happens, things will start to click for you, so hang in there.


I'm not a great guru on burner tuning, but pulsing as the forge heats up is not uncommon.  To me it looks like your gas pressure is too low to keep the mixture right.  My forge will pulse like that when I try to run it with too little gas pressure.


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Still not burning correctly.  Should be a steady roar.  Very possible that you have too much burner for that size forge, particularly diameter of chamber, but there are a couple of other (less likely) things that might be in play:

  1. Did you thoroughly dry your liner?  If it is outgassing the flame may be starved.  Home made refractories are typically a false economy IMHO.  Quality materials like 2600 deg F. blanket and Kastolite 30 will give you a much better and more efficient forge.
  2. The burner orifice could be blocked slightly (pipe tape or pipe dope is a typical culprit, but propane can also contain impurities which can throw things off).  Can you get a good stable burn outside the forge? 
  3. It may work better inside the forge once it gets up to a better heat, but that kind of unstable flame is not normal.  Is the air gate fully open?  How far down is the regulator cranked in that video?  What pressure is the regulator rated at?

Also, I can't believe that the manufacturer doesn't stand behind their product enough to assist you in getting it functional.  Whose product is it?

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Still too much blue flame indicating incomplete burn of fuel.  Dons mentioned most of the usual problem factors.

1. I'd do a burn test outside  of the forge. If it burns right than your forge is problem. It might be too air tight. 

2. If you can try removing the front and back of forge to allow more air flow. 

3. Check you wind direction. Sometime a light breeze can blow those oxygen depleted fumes back over the burner intake. That can cause similar burn problems

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I have one other idea.  Most of these kind of burners have an adjustment of the depth of the orifice in the tube.  An inch or less in or out can make all of the difference.  See if you can figure out how to do that and  fiddle with it.  What you are looking for is a steady, rocket exhaust shaped flame, mostly blue in color.

I would have posted this earlier in the day, but I've come down with Covid, and my thinker is kinda slow.  I remembered it a couple of times, but by the time I got to the keyboard, it was gone/  I was just going to bed, and it popped up, so I ran to post before it got away again.



"The worst day smithing is better than the best day working for someone else."


I said that.


If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton


So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.


Grant Sarver

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On 8/2/2022 at 1:30 PM, Paul McC said:

but the more i get into trying to set this up properly, the more im intrigued in the idea of investing in a larger forge

And there is that slippery slope; right there ;)

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"The way we win matters" (Ender Wiggins) Orson Scott Card


Nos, qui libertate donati sumus, nes cimus quid constet.

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You're still pretty far off... you aren't getting enough air, and or gas pressure.


You want to see a constant, high yellow, almost roaring flame coming from your forge.


A mostly blue flame... is a sign of very low gas pressure. I'd guess that to be around... maybe 5-6 psi? Just from the video.

A venturi style burner needs much more than that to work right. Like 20-30 psi.


Mine is a totally different setup than yours, but this is much more along the lines of the heat you want to forge with/at: you can see the flame coming up between the bricks.


I use a forced air setup with a bounce house blower, and run about 6-10 psi of pressure- because the air blower provides the air flow- not dependant on the venturi effect from the gas flow.






Edited by Welsh joel
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Can you post us a close up picture of your regulator?


Follow that with pics going from it to your burner? See if we can figure out what's happening for you.


I built a coffee can forge for my brother- it uses a small 3/4 burner that is similiar to a Mapp gas torch head. No venturi, just air holes on the side.


It will get medium to high yellow heat.


Just another note too-

Sometimes, the forge just needs to heat up before she'll burn right.


Once up to a decent inner heat- it kind of smooths out a bit, and you can run more air, more gas than you'd think.


The entire inside of the forge is now an ignition source. Instead of relying on just the flame from the burner staying lit/alive.

Edited by Welsh joel
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  • 2 weeks later...

Hi guys,
Thanks again for all the advice everyone has been offering. Its taken me a while to get the time to hop on here and post another reply.
I will post the videos in a seperate post after this one just so its not all grouped together and annoying.

In the first video i show that i have managed to get a bit of a better flame but im not sure its still quite right,
It seems like there is to much yellow flame blowing out of the front of the forge. Also it shows that i punched a bit of a hole in the back to hopefully allow a bit more airflow.

As per a suggestion from Geoff Keyes, in the second video you can see that i get a bit of a more consistent burn out of the flame by adjusting how much the burner
is inserted into the side of the forge.
You can see in the third video i have maked a line on the stainless tube part of the burner which shows how much i have backed 
it out of the forge. I drew the line when it was more or less flush with the inside of the forge lining.
I had also put an old triangle file in the forge just to see if and how long it would take to heat up.

In the last video (i added just for curiosity sake) once i finished this round of test firing, there is a reasonable amount of steam/smoke wafting around the outside 
of the forge. I believe that it is coming from the sides of the forge itself, so even when i get it running correctly i dont think this little forge is going to hold up to too much.
But it should at least get me through the couple of heat treats i need to do for now while i contemplate the option of ordering a small Devil Forge setup.
Within the 5 or so minute that i had it running, the outside of the forge became to hot to touch, not hot enough to burn you but hot enough that you couldnt lay your hand on it for more than a second before it was uncomfortably hot.
I have often wondered how hot the exterior of a properly insulated forge gets while its being used


I did start by lining the inside of the forge with a refractory mortar hoping that it might help, but after the second coat i realised that i screwed up and took till after
the third coat for me to accept that i had screwed it up and i ended up having to chisel it all off from the inside, which half of it had bubbled up anyway so it came off 
reasonably easy. After some reading up i came to the conclusion that i put it on to thick and didnt give it enough time before starting another coat.

As for the request for a picture of the regulator that im using, it is just a cheap generic chinese knockoff type to go along with the rest of the cheap chinese knockoff type of burner that i brought, which i now thoroughly regret but am to limited for money that i have no choice but to make do with what i have.
I am using a 4kg camping gas bottle, not that it really matters, i just thought i would state it for claritys sake.
As i mentioned in an earlier post, i dont have a pressure gauge so i dont know what pressure i am running it at, but i have just opened the regulator fully and then just used the needle valve to adjust things, not that i have been able to get any sort of adjustment out of it apart from how intense it is.

The other two photos show the choke and nozzle tip for the gas, though i am not sure how good this one is.

As you can see by the picture the nozzle does not protrude into the tube very far at all, the tip is bearly below the lip of the tube, but it is already bottomed out on the adjustment thread, though i have no idea if that matters or not.
Also, looking at other people making homemade burners, most people use a Mig tip, and i believe they are a 0.030'' or 0.7mm hole.
The hole in the tip of my burner nozzle is about 0.050'' or 1.3mm. Will this have any effect of how the burner is running?
If it is better to have the smaller hole, i can drill the nozzle and tap it for a Mig tip. That would also extend it and give me more room for adjusting the depth of where it sits

Though i know that i will have to buy or make a proper forge for any sort of future work, putting the time and effort into getting this little thing running properly, even if it only lasts one or two cycles will give me far more knowledge and experience than i would have received from buying a forge and having it run properly right out of the box.

I look forward to the next round of advice and suggestions from everyone.





Edited by Paul McC
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Hmm... yeah, she's not getting enough air. I wonder if your regulator isn't working properly? It's marked correctly for 30psi. An adjustable one with a guage might do you more justice.


If there isn't enough gas flow pressure, it won't properly draw air.


Your flame is too... billowy. Too soft. It should look more forceful, like a jet almost.


It's just not getting hot enough.


A .050 tip is big. Most people recommend .025 tip for use.

That can affect how your gas flow draws air into the burner. I won't pretend to know the math... but there are specific numbers for it that have been worked out.


I'd try changing out the tip first, and work from there.


But, do one thing at a time- and test the differences from there. Easier to keep track of performance that way.


Www.iforgeiron.com is another forum site- there is several gentleman there who have many years developing home built burners. Some great information.

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Can't view videos now, but on quick look it appears that you have your orifice screwed fully in.  I would move the orifice outlet back further and see if that increases the induced air.  Don't move the air gate, just back the burner tip out of the casting about 1/2 way and adjust the lock nut to suit.  To induce more air in a naturally aspirated burner first try adjusting the nozzle outlet further away from the mixing tube, then try increasing the gas pressure, finally try reducing orifice size



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