Leaning temperature control

[North Idaho Forged]

I just built my first forge and I need to quench my first knife. Should I buy a thermal coupler or just learn how to control the temperature by the color of the steel?

 

[timgunn1962]

Both?

Colour can be a very precise indicator of temperature when read by a properly calibrated instrument. The thermocouple can be used to provide a calibration reference for your eye.

Before the days of Infra-Red pyrometry, there used to be a non-contact pyrometer for measuring hot surfaces that used an electrically-heated wire. The operator would hold the wire between his eye and the surface being measured and adjust the heating current until the wire "disappeared" as its temperature matched that of the background. The wire temperature was then read off the instrument.

You can do essentially the same thing with the tip of your thermocouple.

 

[Stacy E. Apelt - Bladesmith]

While Tim's info about early temperature measurement is correct, I would like to mention that staring intently into a 1500F forge to determine if the TC is the same color as the blade can severely damage your eyes.

Another issue is that a forge is hard to run at that low a temperature. You need to learn to read the blade color to some degree.

The alternate answer is - Building a PID controlled forge will allow the forge to run at HT temps accurately. See the stickies for more on that.

 

[North Idaho Forged]

Sound like good information. Thank you for the answers. I will order one and see how it goes this weekend.