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Calibrating an Evenheat Oven

J

John Frankl

Joined
Oct 16, 2001
Messages
1,917
I have an Evenheat Knifemaker's oven with which I am generally satisfied. But I have read a lot about double checking the temperatures on the Set Pro Controller. I have a good thermocouple and digital readout. What is the best way to use it to double check the temps the oven is giving me?

Thanks,

John
 
John, I have no idea what the "best way" is, but I bored a hole the size of the thermocouple through the door to insert the probe close to where the blades will sit. It fits the thermocouple snugly. Watching the two temps during a run allows me to get an idea of not only how they match but how the furnace acts inside. Bear in mind that if the +/- error on the 'couples is on opposite directions, not to get too excited about some variation between the 2. I'm used to seeing 20-25*F. Check your manufacturer's error specs to calculate tolerable variations in readings.

If you try this, be sure to remove the thermocouple prior to opening the door! They bend REAL EASY at 2000F! :eek:

PS: Kaowool plug the hole when not used for the probe.
 
You can get special cones from ceramic supply stores. The cones melt at very specific temps and can help you determine the temp is where you place the blade as opposed to the overall temp of the inside of the oven.

Mostly what I do is run a test batch of 9 small pieces I have marked 1-9. I start 100 degrees below the recommended soak temp and do a quench. I increase the temp of the oven 25 degree and do another test. I continue until I have went 100 degrees above the recommended soak temp. I then clean up each piece and record the hardness on the Rc scale. I then break each peice and examine the grain structure and see which one looks the best. I seem to stay within 25 degrees of the recommended heat treat specs most of the time.

Something else to think about when heat treating is Higher temp means less soak time and lower temp mean more soak time. Meaning if your oven only reaches 1900 degrees and the soak temp is 1950 for 5 min you can experiment with increasing the soak time and still get satisfactory heat treat.
 
If you buy cones, John, buy a range and bracket your target range. The popular brand is called "Norton Cones". They are highly regarded. If you search on that name you can get to their website and read their instruction pdf.

The only problem with the cones is that they are somewhat "interprative". There is a "time at temp" component to their behavior. They "slump" as a function of how long a specific cone is at temp. They are also intended for a certain rate of change (x degrees per hour). Like Arthur said, the temp is accurate and repeatable as long as conditions are repeated. Once you learn to "read" them, you can immediately tell what went on.

I did a series of test runs with a range of cones at several times and temps. Repeatabiility is excellent. Cost is low per run, so you can put target, high, and low temp cones in with your run as a verification things went ok on every run.

Personally, I would be cautious about using them to tell if your thermocouple's ok until after you are used to them in "good" conditions. In other words, don't use 'em for the first time to try and find out if things are screwed up.
 
Thanks guys. I'll go with a hole in the door first, since I have a good thermocouple+digital readout. Plus I like drilling holes in things:)

John
 
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