Tempering in sand

[dickb]

I forged a couple of knifes from 1084 steel and hardened them at the forge. The dimensions are 1/8 th of and inch at the spine, about 1 inch wide and 6 inches long excluding the stick tang. 

I brought them home to temper them in my gas oven. I was aiming at 450 degrees. 

I put them on a rack in the middle of the stove and put a thermocouple probe next to them. (Klein tools multimeter MM200) 

I set the oven to 450 degrees and monitored the temperature as indicated on the multimeter. I found the oven temperature varying by plus and minus about 50 degrees around the 450 degree setting so I reset the oven to about 400 degrees and let it cycle up and down for about a half hour.  As far as I can tell It tempered okay, Holds an razor edge and hasn't chipped or broken under heavy usage. 

Now the problem is, I am using a precision hammer (Harbor Freight 3 lb engineers hammer $7/50) and some unknown brand of smithing coal and an anvil of unknown origin, and I would like a more precise way of heat treating at home. 

I am thinking next time I will bury the blade and the thermocouple in a two inch thick layer of clean sand and use the temperature indicated by the meter to adjust the oven temperature control. 

Hopefully the thermal mass of the sand will prevent the large temperature swings. 

Any comments would be appreciated. 

P.S. Maybe that's why my roast chicken always turns out burned to a crisp. 

P. P. S. The blades seem to be pretty rust resistant.

 

 

[dickb]

I posted this question yesterday, but it seems to have up in smoke, don't know what happened. 

I forged a couple of knifes of 1084 steel. Dimensions 3/16 inch at the spine , one inch wide and 6 inches excluding the spike tang. Fully hardened them at the forge and then brought them home to temper in my gas oven. I set the oven temperature to 450 degrees and put a thermocouple next to the blades. (Klein tools multimeter MM200) . I noticed the temperature swing plus and minus about 50 degrees so I lowered the oven temperature control to 400 degrees and let it swing from about 350 to 450. I figured I could retemper it if it came out too hard. The gas oven is about 50 years old so maybe that's why the temperature swings so much. 

They seem to have come out  okay, takes a good razor sharp, durable edge and keeps the edde very well 

But I would like a little more precision.  I would like to bury the next one I forge in a two inch layer of sand and also bury the thermocouple alongside. My thinking is the large thermal mass will prevent the large temperature swings and I can monitor the temperature of the sand and the steel will follow along. 

Has anyone used this method ?

Any suggestions would be appreciated

 

If you look through this web site, you would notice we have an entire section for knife making, and your post, being about blade work, was relocated there.

 

[timgunn1962]

The sand tray is a pretty well-established method for dealing with temperature oscillation. It works.

I'd suggest an ebay search for "TM902C". It'll bring up lots of suppliers of a type K pyrometer for 5 or 6 bucks delivered. The thermocouple supplied with it is a 3' long glass-fiber-braided thing that is good to about 400 degC/750 DegF and is flexible enough and thin enough to shut in most oven door seals. Downside is the degC-only readout. With a suitable type K thermocouple, the TM902C will read to about 1368 degC, the limit of the typeK table. I've had several on the calibrator at work and accuracy is as good as any of the big-name pyrometers at 10-40 times the price. 

[dickb]

Thanks Tim.

What I have been using is a Klein Tools Multimeter MM200 . It has a with a type K thermocouple probe with a range of -4 to about 1800 degrees fahrenheit Plus or minus 3 percent. Long braided fiberglass leads, etc. per the manufacturer's spec.

I just did a preliminary test and found the 3 percent figure is way off, not even close enough for government work. Probably closer to 10 percent. 

I enclosed the last 6 inches of the probe in a plastic baggie and dipped the tip into 212 degree water and got an indicated temperature of 180. Out of curiosity I'm going to order a TM902C and double check everything, 

 

 

 

 

[Bo T]

You might also try an everyday oven thermometer. Use the sand to level out the temperature fluctuations.