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Gas Forge

Jymm Hoffman

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  • 2 weeks later...

This is my latest, larger 2 burner for a customer. The outer shell is 12 inch long by 15 inches wide and a hard shell interior using ram refractory over blanket, including the top. Third photo is a couple of minutes into a test firing.

Looks great - I especially like the door design. What type of 'ram refractory' are you using? I'd like to try something more substantial that what I'm currently using which is furnace cement and and ITC100. I coated the ceramic wool first with high temp (3000 degree) furnace cement (built up in thin layers) then a top coat of ITC100 )also a couple of thin layers). The cement provides some protection for the ceramic wool and the ITC100 reflects heat back into the forge. However, even the combination of the cement and ITC100 requires some ongoing maintenance as it tends to flake and/or chip. What I'd really like is a cement that would make a 1/2" - 3/4" lining on top of the wool and stay rigid without flaking. Applying cemen/ITC100 on wool doesn't lend itself to a strong shell. I've considered fabricating a cylinder of steel lath (like stucco lath, placing it on top of the wool and then applying a thicker layer of furnace cement to the lath. Then coat the cement again with ITC100. My theory is that the lath would provide a stronger foundation for the cement and the cement/ITC100 would provide enough insulation to protect the lath.

Any thoughts on this approach?
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I really like the swing door on the forge and the little side door looks like it would be quite useful.

A thought on the lath for the forge. As it would be made of steel it would expand when heated and contract when cooling which leads me to think it would cause the cement to crack and if it was such a thick layer could cause large chuncks to fly off.
Just a thought.

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  • 4 months later...

As the buyer of this forge, just wanted to provide a (long overdue) report:

This is an outstanding forge! I had been using a homemade freon tank single burner atmospheric propane forge, and a coal forge for bigger stuff. I'd been wanting to build a blown forge ever since I used a friend's to make damascus. After pricing parts and material, and considering the learning curve, it was an easy decision to just buy one ready to go from Jymm.

The best thing about this forge is its controllability. It easily adjusts from welding heat down to a whisper for forging small stuff, with as much reducing or oxidizing atmosphere as I want.

The cast interior is solid as a rock. There has been no cracking and it is impervious to flux.

It seems to be a bit more economical on propane than my atmospheric gasser as well.

For anyone who's on the fence about atmospheric vs. blown, or build vs. buy, I heartily recommend talking to Jymm.

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  • 3 weeks later...

Sorry for not responding sooner, been really busy this fall, lots of weekend stuff, etc.

Freddie, thanks for the good report.

Dan I sent you a private message. If it does not come through, contact me through my web page: www.hoffmansforge.com

The entire exposed surface is the same ram refractory I have been using on the bottom. For a few years I tried coating the upper blanket with 3,000 degree mortar. I experienced the same problems of when it eventually flakes and breaks off, it pulls blanket with it. The new version using ram all the way around (backed by blanket) has solved this problem. They are much more resistant to damage from banging into the top and no worries about flux touching anything. I believe I previously posted the contact I use for my refractories, Dixie. If still needed I will try to remember to post it again.

I still simply use blanket for the doors. One, I found it difficult to get a really good seal if I used the ram on the door, might try a couple more on student forges I will be relining the tops before I start my classes in December. I am also trying to keep the cost down on these, so adding one more thing normally adds a lot more time than expected. I am still working on the costs. I don't really want to go into the business of building forges, as I prefer to pound hot iron. However, I will occasionally make one or two available, especially for students and other smiths I meet through IForge, etc. Plus, I am not a fabricator, my electric welds are not pretty, but they do hold... I prefer forging and forge welding, did I already mention that? :)

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  • 2 months later...


Excellent forge design, Plan to be building a similar one with fire brick. Have a question though. I have a forge that is 800 long 200 across (interior measurements)and I have three blown burners on it based on the Indian George design. Both the gas and air flow on each burner can be opened or closed with a gate valve and the burner itself is 1.5 inch pipe. Is this too much burner for the size forge I am using?



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