Muffle for tempering

G

gshamr

Joined
Jan 18, 2002
Messages
178
This is initially directed at 69 knives because he recommended a muffle for tempering in the last thread I started. Thanks for the info.

Maybe there are some appliance repairmen that could chime in.

...........................

I wonder whether different brands or ages of ovens differ greatly in their temperature fluctuations. I have a 5 year old GE electric oven and bought a $10 Farberware oven thermometer. I found that I have to set the oven at 510 degrees to show 500 degrees on the thermometer. I checked it often during the tempering cycles and it did not fluctuate by more than 2 degrees either way. I probably checked it every 20 min.

Right now I'm testing it at 375 after reading some of your earlier posts on the subject. The oven temp appears spot on at 375 and I see no fluctiations either. I will watch it over the course of an hour and see what happens, but in 30 min so far it has not fluctated.

I can understand my oven thermometer being off by 20 degrees but it should still show large fluctuations with cycling. Could it be that you have an older oven or a different brand that functions differently? Maybe my oven has a more controlled way of fluctating the elements on and off? Any thoughts by anyone?

Gerry Hamrick
 
Is it a convection oven with a fan in it or does it have 2 elements in it, that turn glowing red hot when on a heating cycle and return to black when off?

Another thing I recommended was using an inexpensive digital multimeter with a thermocouple; your typical oven bimetal thermometer is not its equivalent.

When I did my initial testing I also had a bimetal oven thermometer on top of the muffle, outside and it did not fluctuate either whereas the thermocouple reading fluctuated by about 100 degrees.
 
It has the two glowing elements.

If the issue is that a simple oven thermometer does not register quick fluctuations, then I need to buy the multimeter/thermocouple. What types of brick and mortar store have that?

I also had an idea.... If I use sand, I can leave it in the oven and take the blade out with tongs to cool. When it's time for the next temper, I can use tongs and an oven mitt to bury the blade again and the sand should already be hot and bring the blade up to temper temp more quickly.

Don't pop my bubble and tell me someone already thought of that.:D

Thanks again for the info.

Gerry
 
Hehe, that should work great, though there are those that recommend a 24 hour period between tempers.

Our Canadian 'Harbour Freight' equivalent type store has the multimeters with thermocouple on sale regularly for under $10.00.
 
Crap, I was just near Harbor Freight today. I can afford $10.00.

Thanks again.
 
Gerry - you can put large masses in the oven to get it to maintain temp without such large swings. It will need to equalize, even after it preheats. If you have some cast iron pots and pans, they will do wonders at keeping the temp from swinging so much.
 
Thanks.

I have a cast iron pot, some barstock and some mild steel. Hopefully I won't cause the bottom of the oven to collapse.
 
I use some fire brick that I had left over from a forge build. 1' thick that I lined one of the racks with keeps the oven from running so much as well. But It's in a medium size toaster oven.
 
I just found this post made by Stacy and thought it was well worth quoting in this thread. As usual, he says it all in just a few words...

bladsmth said:
The conversion of structure in tempering is a function of time and temperature. Time is far inferior to temperature. You could temper for many extra hours and not affect the hardness more than a point or two. Temper at 10-15 degrees higher, and the hardness can be greatly lowered in two hours.
BTW, I recommend tempering for two ,two hour cycles.
Stacy
Click to expand...


It is worth knowing that your blades aren't becoming hotter than you like. Any blade exposed directly to the oven without a muffle of some sort should be suspect. IMO.
 
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