I am currently working on building a new propane forge. I plan to use two inched of 2600 degree kaolwool, soft firebrick, and coating everything in ITC. The forge will be 12 inches long and use 1 frosty T burner. My plan is to build it an and 8 inch diameter pipe. That would leave me a 4 inch chamber which is plenty big for the knife work that I do, and I have a coal forge for oddly shaped work. 

My question is, are there any downsides to a small forge other than what you can fit in it? I don't want to use any more gas than I have to so my whole goal is efficiency. In other words, why would you make your forge chamber larger than the your steel?

 

Thank you guys for your time and wisdom

You need enough volume that there is some "hang time" for the burner's flame to transfer heat to the forge's interior.  You usually take care of this by sizing the burner to the forge.  

Try not to exceed a two to one length to diameter ratio. What you gain by reducing internal volume will be more than lost in poor burner performance.

I don't have anything to add about forge chamber shape and burner size/numbers. I will however say ITC doesn't make an appropriate product for a propane forge kiln wash. You'll get much better and longer lasting results using Plistex or Matrikote.

Frosty The Lucky.

10 hours ago, Frosty said:

I will however say ITC doesn't make an appropriate product for a propane forge kiln wash. 

Ok, I will start looking for a better alternative. What is the problem with ITC 100 as a kiln wash, does it just not last very long?

The original formula was easily scraped off  interior surfaces, but lasted well enough otherwise; but is was no better than Plistex for way more money. In recent years its price has skyrocketed, and, going by the descriptions several people have posted, I must conclude that the original overpriced and underfed formula has also been further cheapened.

In my limited experience, one advantage to having some extra room is that you can heat you materiel indirectly, thus keeping the harsher propane flame of your delicate work and have more even heating of your piece.  Forge shape and burner location/where it points can solve a lot of that issue. 

Also, a forge that is very close to the same length as your blades will require constant attention and manipulation front to back to get even heating from tip to tang.  Though, with the tip containing less material than the belly of the blade, some attention and manipulation will always be necessary in a flame based forge (as compared to kiln or oven where the heating is less direct) 

 

With a 12" long forge, if you frequently do blades that are about the same length you may want to consider 2 smaller burners or a ribbon burner to get a more even heat. 

One issue is that 1/2 T burners are about the smallest that can be practically made due to availability of small orfice mig tips.  I've seen a few people get around that by using the nozzles from 3D printers, which are smaller and have a lot more orfice options available. With this you could do 2 3/8 or 1/4 burners, though it's well outside my knowledge base to suggest any more. Others, like DrFrankenburner and his 3d printed and cast burner parts, have gotten very good results from rather small burners and his thread is a great read 

Capillary tube can be trapped  in MIG tips, to provide the same orifice variety. I would suppose the harder problem to be finding what he'd need in small "T" fittings; would love to be wrong in that assumption

Thank you guys for your input, I've decided to do a propane bottle forge instead. I'm starting with a singe 3/4" frosty T burner. Which according to my calculations should heat up the space nicely. If I need more heat I can always add a second burner. I have all the materials so I should be building soon!