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I was recently given an older and very used Johnson Gas Forge. See pictures. I don’t have access to natural gas. Is it possible to safely convert it to propane? This is all very new to me. I have tinkered around with a homemade coal forge but know nothing about the workings and mechanics of gas forges. Any help and advice would be greatly appreciated.  

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Johnson Gas Appliance supports their products contact them with the model # and request a manual, parts list and order form. I have a Johnson Gas Appliance mod 200 1/2 forge very much like that one and they carry the parts. Conversion is a matter of changing the jet and perhaps a little adjustment. The manual will cover the specifics.

Yours is in much better condition than mine, I've never put mine in service. They're gas hogs in case you didn't know.

Frosty The Lucky.

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Thanks for the comments. I appreciate it. Unfortunately I contacted Johnson gas and they said they were not the manufacturer of this forge, in which I don’t understand. It’s obviously a Johnson Blower. But then again, other than the writing on the Blower and the specs on the motor I can’t find any info anywhere on the forge itself, no model numbers, nothing. Perhaps some one made it from different parts. Anyways, the only advice they could really give is to try and change out the orifices. So I guess that will be my next aim, trying to learn what size orifice to replace it with. It’s just a little nerve wracking, I don’t want to blow myself up or set a fire in my shop in the process. 
Again, thanks for your help. 
David 

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Not that big of a deal; we bought a kitchen stove and I got to change it over to use propane. Never having done one before I found it simple.  Just swapping out the orifices and tuning the air for the burners. It even came with the proper orifices as a conversion kit.

Is there a propane supply company near you that you can consult with?  Back 20+ years ago I had an ancient natural gas 2 burner counter top  gas ring converted to propane so I could take it camping.  They silver soldered the NG orifice closed and redrilled it for propane and that was it.

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Yeah there is. That’s basically all we have here. Propane.  No natural gas. I understand changing out the jets, though I don’t know how yet. But how would I tune the air for the burners? I turned it on and let the blower work for a minute and played around with it. There is four places for the air/flame to come through. There is 2 large bolts on the back. They seal off the first and last burner or open them up just depending on how much you screw them in. Is this what you mean by tuning the air, or a bit more complicated like modifying the blower to blow harder or lower? Other than that, unless I missed something (in which is very very possible) I didn’t notice a valve on the blower to control the air flow, only a valve for the gas. 
I’m sorry for the dumb questions. I’m definitely a green newbie at all this. 

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Tune it like you would tune a propane forge burner: Neutral to slightly reducing and at the rate that gas hog will burn it I'd try for a true neutral to cut down on CO production.

Does Johnson have online manuals for their systems that you could try to work from?  I'd bet it's similar!

So if you are a green newbie; what are you doing that you need such a large expensive to run commercial forge?  Do you need to throw away hundreds of dollars while learning?

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It was given to me. Other than some propane I’m not out of cost. I do a lot of woodworking, a little welding, etc.  Blacksmithing is just an interest. Basically I love tools. Collecting, restoring.  I really don’t have any plans for it, other than to get it going and tinker with it here and there. Just a hobby. 

A small little neighborhood in central Louisiana 

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I looked and your's doesn't look like my Johnson trench forge. The gas controls on mine are automatic and there is NO 1/4 turn shut off valve. Then stepping back, the: body, legs and lid on  mine only resemble yours. I'm thinking you have either another manufacturer's product or a copy. It's possible someone had parts of a Johnson trench forge and made a frankenforge. 

For  now I'd pull the nat. gas jet, hit the local HVAC supply and get the equivalent for propane. Do NOT tell them what you're doing, you'll start getting recommendation from folk think in "residential heat" terms, not forge terms. It took me a couple years to train the local HVAC supply/service company at the end of my road that I knew what I'm doing. Now they just look up the price and ring me out or answer questions. I don't ask things like do you think "xx" will work in a ? ?" 

They'll check for thread compatibility and should have the equivalent for propane. If not in the bins they should be able to give you the part # to order.

Frosty The Lucky.

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Not sure if this will help, as it is likely for naturally aspirated burners but here are some charts for propane orifices:

  

Information generated using the
“ WARD BURNER SYSTEMS CHART ”
THE KILN BOOK, 3RD EDITION, F. OLSEN

PRESSURE IN PSI
5 10 15 20 25
ORIFICE (DRILL) SIZE
BTUs / hour        
73 14272 20184 24720 28544 31913
72 15503 21925 26853 31007 34667
71 16766 23711 29040 33533 37491
70 19450 27507 33689 38901 43492
69 21155 29918 36642 42311 47305
68 23839 33714 41291 47678 53306
65 30375 42957 52612 60750 67921
63 33943 48003 58792 67886 75900
62 35806 50638 62018 71612 80065
61 37732 53361 65354 75464 84372
60 39689 56130 68745 79380 88750
59 41679 58943 72191 83358 93198
58 43731 61846 75745 87463 97787
57 45847 64837 79410 91694 102517
56 53614 75822 92863 107229 119886
           

Information generated using the
PYRONICS SYSTEM, PYRONICS INDUSTRIAL
COMBUSTION SEMINAR HANDBOOK

PRESSURE IN PSI
6 10 14 20 25
ORIFICE (DRILL) SIZE
BTUs / hour        
73 16750 21713 25590 30708 34120
72 18146 23574 27761 33345 37222
71 21713 27916 33035 39548 44201
70 23109 29778 35051 42185 46993
69 24970 32259 38153 45752 51180
68 27916 36136 42650 51180 57074
65 35981 45752 54282 65138 71342
63 39703 51180 60486 72893 80648
62 41875 54282 63588 77546 85300
61 43736 57384 68240 80648 89953
60 47768 60486 71342 85300 96157
59 49629 63588 74444 89953 100810
58 51956 66689 79097 94606 105462
57 53662 69791 83749 100810 113217
56 58159 75995 89953 108564 119421

 

In my experience orifice size is less critical for blown (gun) burners.  Just use a pipe connection around 1/8" diameter and a GOOD ADJUSTABLE GAS REGULATOR, and you should be fine.  Since the NG orifice is typically larger than the propane one I would expect you don't need to change it provided you have a regulator.

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Ok. I managed to remove the blower tube (for lack of a better description). There is no orifices. This is embarrassing. I’m sure everyone  on here knows where they should be. I was under the impression they were fitted to the end of each tube that blew in to the fire pot. I hate asking but this forum is the best resource I got. I’m literally learning as I go. 
 
See the photos below, this is where I thought the jets would be. Any help is welcome. 

On another note, I turned on the blower the day I got it. Today I turned it on and it wouldn’t turn, sounded like it was in bind, then smoke started coming from the motor. I have several old motors laying around or I can find one easy enough. I’m not too worried about this. No big deal to change that out. It’s just showing me what kind of project this is starting to be. I did have my doubts about the motor. It looked as though it had been around for awhile. 

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Why didn't you follow the gas supply line? Pics 1,4,5&6 show it clearly, 6 is a close up 

The gas jet is centered in the blower intake port behind the choke plate. This allows the impeller blades in the blower to mix the gas and air thoroughly before sending it to the burner nozzles. 

You might want to give the screws, nuts and bolts a squirt of penetrating oil, breaking rusted in bolts, etc. is always a PITA ROYAL. 

Frosty The Lucky.

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Yup I had an electric blower release the magic smoke yesterday; of course the motor had a 1905 patent date on it with OPEN terminals.  I'll see about replacing it with one of the modern HVAC blower motors I have been accruing at the scrapyard.  (And yes I did check the plate and it was single phase 110 VAC and not a weird one.)

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You can see that I topped off the oilers before trying it out.  Open terminals gives me the shivers for public use...Might just need a dunking at the Motor repair place; but as I'm selling this on; I'm going to swap it out with a modern motor.

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