Atlas forge and using a muffle question......

K.B. Knifeworks

K.B. Knifeworks

Knifemaker / Craftsman / Service Provider
Joined
Jul 2, 2009
Messages
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Hey all. General question about gas forges and using a muffle for heat treating and where to best place a thermocouple sensor. I am using an atlas forge and its relatively compact with a 2.5” opening. With this setup how big of a muffle would you use in this smaller forge? Also, would you leave it as a solid tube or drill holes in the muffle?
 
For that size forge I wouldn’t use a muffle, it’s designed to have a swirling flame and it’s easy in most cases to keep the knife on the colder side of the forge. Heat treat in the dark and learn to watch colors and stick with simple steels like 1075/1080 or 8670, use the forge and have fun but save up for a kiln or send blades out for heat treating if you want the best results. I started off heat treating in that exact forge and it was a good learning tool but I found when I went back and checked a lot of those early blades after I knew a bit more they were either softer than I’d like or didn’t harden through the core.
 
Joshua Fisher said:
For that size forge I wouldn’t use a muffle, it’s designed to have a swirling flame and it’s easy in most cases to keep the knife on the colder side of the forge. Heat treat in the dark and learn to watch colors and stick with simple steels like 1075/1080 or 8670, use the forge and have fun but save up for a kiln or send blades out for heat treating if you want the best results. I started off heat treating in that exact forge and it was a good learning tool but I found when I went back and checked a lot of those early blades after I knew a bit more they were either softer than I’d like or didn’t harden through the core.
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Perfect - thanks man. I was wondering about that but was not 100% sure. Any suggestions on the best place or method for thermocouple sensor placement in that forge?

Yep - sticking with 1084 and 8670 and hope to buy a Jen Ken vertical air bath in time for dedicated heat treating.
 
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steelhog said:
Perfect - thanks man. I was wondering about that but was not 100% sure. Any suggestions on the best place or method for thermocouple sensor placement in that forge?

Yep - sticking with 1084 and 8670 and hope to buy a Jen Ken vertical air bath in time for dedicated heat treating.
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The vertical JenKen kilns are great, I have the 30” tall and have heat treated 500-700 blades in mine so far and have had no issues. I only used the thermal couple a handful of times since it’s pretty hard to get the forge to equalize at heat treating temps so all the thermal-couple will tell you is the forge is running at 1800-2000F but it won’t really help with the blade temp. When I would try to use it I’d place it at the opening of the forge.
 
You could stick it in with the blade, maybe beside or underneath? That way it's sheltered from the blast of the burner...
 
I have an Atlas knife forge. I use a thermocouple that I put in thru the rear opening in the forge. However it isn't very accurate that way. Moving the thermocouple back and forth will show variations in temperature. Sometimes as much as a 100 degrees.
I like the Atlas forge. However I've found it difficult to keep it close to the temperature I want. I'm usually over shooting. So while the thermocouple can help you establish a general temperature range, it's not very accurate this way. I've considered drilling a hole on the side away from the flame thinking that might be better. But I've been reluctant to do that so far.

Atlas sells a knife forge that comes with a thermocouple, and presumably a well placed hole for it. However I can't tell from their photos where that is. Perhaps a call to Atlas might help.
 
When using a thermocouple in a forge with a flame it measures the flame temperature, not the blade. In a muffle, placing the TC in with the blade (preferably in direct contact with the blade) it will be much closer to the blade temperature.

As to your use of a muffle in an Atlas forge - it would have to be a small blade and muffle. Schedule 80 pipe around 1.5" OD would be the max size. Throttle down the burner as much as possible and let the forge and muffle heat for a good 15 minutes. Put the TC in the muffle and see what it reads. Adjust te burner as needed to get close to the desired temperature. I don't know if an Atlas burner will run low enough. You may want to build a smaller burner just for doing HT.
 
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