frozen_coyote

Propane Forge Build Critique

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I’ve been reading everything I can in preparation of making a small gas forge. This is completely a hobby thing so this is a bit of an experiment. I wanted to lay out what I’m planning to do and see if anyone has thoughts on what I should change if anything.

The plan is to use an 8-inch diameter piece of stove pipe that is going to be 10 or 12 inches in length. 10 inches puts me at 282 cu/in or 339 cu/in at 12. I’m going to be making a ¾” Frosty T burner. I’ve read that 1 properly tuned T Burner is sufficient for sizes of 350 cu/in and below. Will the 12 inch length pose a difficult setup for one burner or is that a fine size?

The build is going to be two 1-inch layers of kaowool. Put the first inch in, wet it with a spray bottle then use rigidizer. Then wrap the 2nd inch and do the same. I’m going to then put a ¼” to ½” layer of kast-o-lite in the forge (just the bottom or all the way around?). Then it’s a layer of plistix and it’s built.

How does that sound? Hoping to catch any mistakes before making them. Thanks

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Big possible mistake, your sizing.  Your math is right if you were planning 1 inch of blanket only for a 6 inch internal diameter(ID) forge.  An 8 inch pipe, minus 4" for blanket(2" per side), minus 1" for kastolite(1/2" per side) yields an ID of 3 inches.  I am guessing you subtracted the 2 inches of blanket from the 8 inch pipe for 6 inches or did you square the 3 inch diameter instead of the radius?

Two inches of blanket and 1/2 inch of kastolite for the 3 inch ID would be ~71 in³ at 10 inch length or ~85 in³ at 12 inches.  

If you were expecting 3 inch ID, great.  One 3/4" burner might be too much, maybe not.  If you go to 12 inch length, your forge will be fairly small and long which may hinder the burner performance.  You might think about 2 smaller burners or a shorter forge.

I had a forge at 3 1/2 inches ID by 12 inches length with a 3/4" burner.  It worked well.  Made out of a refrigerant cylinder based on Ron Reil's website.  

If you were expecting a 6 inch ID, you need an 11 inch case.  The larger disposable helium cylinders and 20lb propane cylinders are around 12 inches.

As to the kastolite on the bottom or all the way around, that is personal preference.  Just the bottom will be less mass in the forge which will heat up faster and possibly to a little higher temperatures but the walls and ceiling will be fragile to piece bumps.  If you are clumsy with hot metal, armor the walls and ceiling with kastolite.  It will take a little longer to come to temperature and maybe not get to as high a temperature but it beats poking into the blanket.  If you are only half clumsy, the kastolite can be thinner.  

Experiments are great.  Sounds like you do your homework, you'll have a hot forge in no time.

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1 hour ago, Another FrankenBurner said:

Big possible mistake, your sizing.  Your math is right if you were planning 1 inch of blanket only for a 6 inch internal diameter(ID) forge.  An 8 inch pipe, minus 4" for blanket(2" per side), minus 1" for kastolite(1/2" per side) yields an ID of 3 inches.  I am guessing you subtracted the 2 inches of blanket from the 8 inch pipe for 6 inches or did you square the 3 inch diameter instead of the radius?

This is why I knew it would be a good idea to ask before starting the build. That was a huge oversight on my part. My brain just thought, "8 inch stove pipe minus 2 inches for the kaowool so the diameter is 6 inches making the radius 3." That would have been a really stupid mistake to make. Thank you for pointing that out. 

My original plan was to use an old propane tank but after doing a bunch of research I got scared off the idea. Basically everything boiled down to: take off the valve, fill it with soapy water (or nitrogen or car exhaust fumes (!?)), let it sit for some amount of time, then cut into it and you'll probably be okay. Inevitably in these discussions 2 or 3 comments would pop up saying something like, "My cousin Steve used to cut open propane tanks all the time with that soapy water method. Then one day the tank exploded anyway and that was the end of Steve." All this to say, I'll have to recalculate but I'll most likely opt for a steel (non-galvanized) 5 gallon bucket. 

Thanks again for pointing out that mistake and saving me a good amount of time/resources.

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He tanks don't have the explosion risk with abrasive or saw cuts.  All empty tanks have an explosion risk for O-A cutting.  I pick up a couple of sizes of He tanks at the scrapyard to hand out to folks wanting to build a propane forge. Got them hanging from a wire up high in the shop.

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Don't feel bad, I suspect it is a common oversight on the first forge.  Maybe not, maybe just me and you.

I can't comment on the propane tanks as I don't use them for this.  Their wall thickness is a bit heavy for me.  My last forge was cased with sheet metal.  

I look forward to seeing your progress.  Anything in particular you want to forge or more general hobby work?

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Sounds like the colder weather has people building propane forges . I’m planning a small gas forge also . I have both 20& 30 lbs propane tanks at my disposal , the valves have been removed & tanks outside for over a yr. The 20 lbs- 452 3 in with 2” wool alround , 30 lbs - 750 3 in. . 

My old forge has a 3/4 Riel burner I think was the fellows name ( built 6 yrs ago) didn’t use it much , couldn’t get steel hot enough . Doing homework now know why inside wool 577 3 in , to much space & didn’t center burner well.

I work on knives , hatch’s & tools mostly . Thinking the 20 lbs tank would be big enough with single burner , with extra layer of wool on 1 end & flat bottom . Not exactly sure what kalo lite is , but I do have 3000 degree refractory cement , will have to check name brand ..

Any info very much appreciated . Plans are easily changed , iron not so easy.

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It would be even better enough with two 1/2" burners; this would allow you to do most of your work with 1/2 the fuel, by sliding in a temporary baffle wall, and running a single burner.

If you had used a Riel burner with the MIG contact tip changes (that are recommended on his burner Page), that burner would have got plenty hot enough.

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