How to use a thermocouple with a muffle

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syvmn

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Apr 5, 2009
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I have a 6" inner diameter forge with a 2" muffle centered in the forge propped up on thin slices of firebrick. It's not attached in there just resting on the firebrick so the flames can swirl around it.

My question is how to use a thermocouple with this? Should I drill a hole between my two burners through the side of the forge and then a hole in the muffle for it to fit in?

My concern is if I permanently seal the thermocouple on the inside of the forge if I will be able to get the muffle out. Is there a good way to just "plug" the hole in the forge so I will be able to move the thermocouple in and out if I need to replace or remove the muffle?

Thanks for any help.
 
I ordered a Tabasco from Chileforge and they added a probe port for me on the side as an option. They are throwing in some extra insulation (I assume ceramic blanket) to plug the hole with when not in use. Seems like a valid way to do it, but I'll know more once I start playing with it.
 
Cut a soft fire brick to fit the end of the muffle as a plug. Drill a hole in the center of the plug to fit the TC sheath. Insert the sheath all the way in. Use satanite to cement it in place.Insert the TC, and pack the sheath with wads of kaowool. Don't pack the 1" where the TC end is. If not using a sheath, just install the TC through the plug.
When the firebrick plug/shaeth/TC assumbly is done , place the plug assembly in the muffle from the back side.
Make a second plug with no holes. Place the blade in the muffle and install the plain plug in the front end of the muffle. The TC should read the muffle/blade temp very accurately. Some people place a small piece of charcoal in the muffle for oxygen consumption. Try it it and without and decide if it matters for your setup.
 
Only problem is that my forge isn't open on the backside so I would have to drill a hole in through the back to get the TC in there.

Also, people close up the entire muffle? I was going to leave the front end open.
 
syvmn said:
Only problem is that my forge isn't open on the backside so I would have to drill a hole in through the back to get the TC in there.

Also, people close up the entire muffle? I was going to leave the front end open.
Click to expand...

It's a leap of faith ;)
You can choose between peeping the glow and let some oxigen playing with Your steel
OR seal the front and trust in Your TC, wich in the "closed muffle" configuration should read better the real temperature of the steel (i.e. less variation in temperature inside the muffle). Also the kind of steel and it's attitude with decarburation may push You in a direction or another.
Bye :)
 
Hmm. I dont have a floor in mine, its just round. Maybe I'll put in a floor so I can pinch my pipe like you did over on the side. Great idea!
 
If you seal both ends of the muffle with a bit of charcoal inside how can you tell when the blade itself is up to temp and it's time to begin timing the soak? Begin timing when the temp inside the muffle is right and trust the blade is also at the right temp?
 
If your forge doesn't have a back port, just reverse the plugs. Put the TC in the front and the solid plug in the back. You can leave the back open if you don't want to have the muffle sealed, but you will be far better off with a closed muffle and a small chip of charcoal.
 
I just received that same thermo couple and it is plenty long and will have to be cut to size along with the ceramic sheath. I am glad you asked the question because it is exactly what I need to know as well :)

A question I have is do you place the blade right at the same spot as the thermocouple in the muffle pipe?
 
Good info here.
When the blade is in the muffler, should it be on some kind of rack to keep it centered in the muffer and off the floor and sides? Or would it be ok for the blade to touch the sides or floor?
 
The entire muffle and its interior should be a consistent temperature, so uneven heating isn't usually a big problem.
However, if the muffle is big enough to allow, it is a good idea to place the blade on a "V" trivet or holder to allow easy removal when ready for quench. The spine should be down toward the muffle wall. A small piece of firebrick with a groove works well for the holder. An alternate is a strip of 12 gauge stainless screen that is cut to just a tad less than the muffle ID. This will allow it to sit about center. It should be inserted with enough room for the end of the tang to stick off the shelf to allow a quick grab with the tongs. While mentioning tongs, make sure you have a pair that will reach inside your muffle. It is a funny situation to discover that you can't get the blade out because all your tongs are too fat to slip in the pipe.
 
Hey guys just got my thermocouple in today and am planning on trying it out tomorrow.

Do I need any special connectors for the wire that was included or can I just wrap the exposed wire around the terminal spots?

Thanks!
 
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