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Saturday, October 15, 2016

Let's Make a Knife, pt 3

Picking back up with Step 13...

Heat treating foil is important! Since mere mortals cannot afford to have controlled atmosphere kilns in our homes, we can wrap our parts in foil for the heat treating process. It forms a barrier between the part being heated and the air around it. This stuff cuts reasonably well with a pair of quality scissors. Wear something to protect your hands, it's sharp stuff.

Size up your stainless foil. It needs to be large enough to double fold each seam.
I usually add a little piece of paper near the handle. The idea is that it will consume any oxygen left in the bag during the heat treat process.
Make the first fold. This just happens to be a good use for a Warrinton pattern hammer. It works great to really crimp down the fold.
I drag the hammer over the fold to crease it tight. Once the first fold is crimped, fold it again and mash it tight.

Fold over one end...give it the same treatment as the main fold. Sometimes, instead of dragging, I tap the seam with the hammer.

Doubled up. Repeat on the other end...

Complete bag!

Step 14: Into the kiln! I have three other knives getting the treatment along with this one.

Fired up and ramping to 1850 degrees F. It will hold there for 7 minutes and shut off the coil. The Set-Pro controller is programmable, but not as user friendly as more advanced units. That doesn't matter to me. I use the same steel, and don't need different "recipes" saved in the controller (this one holds at least 3...I forget). If I start working with more steels, or steels the require complex "recipes," I will look into investing in a more advanced controller.

The seven minute soak time is up...time to pull them out. A2 is an air quenched tool steel. It needs only to sit in still or slowly moving air to quench it. Other steels require water (W1) or oil (O1).
Step 15: When they've cooled enough to hold in your hand for 10 seconds, its time to temper. Run your oven up to 325-350 degrees and put them in for an hour. You can double temper if you like. After the first temper, let them cool, then back in at 325-350.
Shiny bags ain't so shiny no more! At the temperatures we're dealing with, all sorts of oxidation takes place. Even stainless steel ceases to be, well...stainless.

Our paring knife, post temper. It needs some clean up and a finish grind on the bevel. I think we'll cover that tomorrow.

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