Muffle size?

[PaMtnBkr]

In a gas forge I often see people recommending using a pipe to act as a muffle to ensure even heating of a blade during heat treat. If you have a 12" deep, 3" Dia Chamber, what size muffle would you use? I have access to SS tubing/pipe and want to make sure I cut it only once! Thanks, Don

 

[Rick Marchand]

Unfortunately, I think your forge cavity is too small for a muffle pipe rig. You need room for the burner flame to expand. Throwing a 2" pipe in would choke out the performance and stress your forge components. What angle does your burner port come in at?

 

[Stacy E. Apelt - Bladesmith]

In a 6" chamber a 2" pipe will fit. approx. 1/3 the chamber diameter is max.

 

[PaMtnBkr]

Ah, OK. I'll just make a larger forge and make due w/my smaller one for now. When I make a larger forge, how deep will the muffle go assuming I make a 12" deep forge? I would assume you want room for the flame to enter from the rear and front of the muffle? So maybe 8" long? Flame will be entering from side of forge but near the top so that it swirls and not a direct blast to the center of the forge. Thanks guys! Don

 

[Rick Marchand]

Here is one I did a few years ago. The pipe is almost too big.
http://www.bladeforums.com/forums/showthread.php/784221-Heat-Treat-Rig

 

[Stacy E. Apelt - Bladesmith]

As Rick''s photos show, you don't want the flame in the pipe. That would largely defeat the purpose. The pipe is usually about the same length as the forge floor. I like to place two small firebrick "feet" under the muffle to allow the flame to heat it all around.

 

[PaMtnBkr]

Got ya! Thanks Stacy! Good call on that!