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Wednesday, March 22, 2017

Knife edge thickness before quench

A little project that will be ongoing for the next batch of knives is to determine the ratio of edge thickness to spine thickness of a knife that can be safely quenched.

Current practice is a dimes thickness with no regard to overall thickness of the blade. Now a dimes thickness on a 1/4" chopper makes sense but on a 1/16" fillet knife not so much.

So going on the theory that the spine and edge will have different degrees of shrinkage and this ends in the edge cracking when it is too thin then there must be a minimum safe thickness versus depth ratio.
Betting some engineer out there could answer this in 10 seconds but this old guy is going to have to use experimentation :) more fun anyway.

What has to be determined:
  1. The minimum thickness an edge can be and safely survive the quench.
  2. Air and oil quench will behave differently, oil be much faster and therefore harder on the edge.
  3. Depth of blade, the deeper the knife the greater the apparent lever effect on the cutting edge as the spine cools. This can cause the edge to tear open or crack.
  4. A general rule of thumb might be easier to sort out, time will tell.
  5. Use of blade will play a factor here but I don't foresee anyone using a fillet knife as a chopper. I tried it once and the knife was not happy, edge held up on mine but without the pins in the holes and the heavy impacts I did eventually break it. (should have chamfered the holes)
The next batch of stainless steel blades made from 0.10" material will have a bevel with 0.01" thickness left before air quenching.

Also have to find a dime and measure it, and this brings up another question. A dime from which country? Sticking with Canada for now unless I have an American coin hiding here somewhere.

Canadian dimes measures in at 0.047" for simplicity that will be rounded up to 0.05"

Will be updating success or failures as they happen

23 March 2017
Knife #1 CPM154,  0.10" thick - edge 0.02" depth 1.28"
Knife #2 CPM154,  0.10" thick - edge 0.03" depth 1.55"

Ready for the furnace

Ready for tempering
Testing was 100% successful on both blades, Top blade needed a little cleaning for the picture since the Condursal blew off as I was removing from the furnace. First sign I did not get the blade clean enough second was a light brown coating that needed to be sanded off.
Actually very surprised that the knives both came out nice and straight. This can be attributed to use of quench plates and a air cooled steel which has a two minute window tooreach a temperature below 600F ideally and up to 30 minutes for room temperature.
Clamping between two plates and tossing out in the snow bank after a minute of air blast to get the stainless below 1000F makes short work of reaching below room temperature.

Really liking the color of the lower blade now if it was only adhered well enough to leave but unfortunately it takes very little to remove the coating.

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