In anticipation of my HT oven build - Aluminum plate setup!

M

Maelstrom78

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Sep 21, 2013
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I'm excited over the prospect about being able to HT my own stainless and the opportunity to get more stuff for my shop. I'm planning on using aluminum plates mounted on a vertically mounted quick release woodworking vice.

I am having some luck finding 3/4 aluminum 6061 T651 plates on ebay. Very little luck finding 1 inch though.

If I have something wide enough for 1-2" around the blade itself I would assume that 3/4" would be thick enough if I am only doing a few at a time. I do do some 3/32 12-13" chef knives but that's about the biggest I typically go. Would like to do some maybe 1/4 bowies down the road though.

Also, is there a consensus on whether blowing the air between the plates adds anything to the outcomes?

Thanks!
 
Sure you can weld the plates together to get larger/thicker plates, but they you WILL need to mill them to get the sides VERY flat.

Air does help, but a fine mist of water also really keeps the aluminum cooler.

Ken H>
 
I only have 3/4" plates. They are 18*3*3/4. After quenching one blade I dunk them in ice water until they are chilled, then dry them off and do the next blade.
 
I personally like at least 2" thick plates

If one has a large supply of 1/2" or 3/4" plates all you need to do is bolt them together.

Unless the plates are really warped or rough cut, you don't need to worry about milling the surface. They work fine as they come from the metal supplier usually.
 
I bought my 2" thick 8 x 12" plates from mcmaster-carr. usaknifemaker has 1" plates as well.

I went with 2" thick because Stacy recommended them, and that's good enough for me!
 
The only reason I use 2" plates is rigidity and more thermal mass. Thinner will work as well, but may need to be cooled if doing many multiple blades. The cooling is only to make them able to be touched and handled without getting burned. It is not for making the quench better. I think people put too much emphasis on cooling them. Remember, the plates can be any temperature below 300-400F to work. In many ways, slightly warmer plates are better in how they will control warp. Ice cold isn't really a good idea at all for many reasons.

My "rule of thumb" would be - "If you can put your thumb on the plates for more than three seconds, they are fine for the next blade."



Lets look at what we want to happen in a plate quench ( stainless in this case):

The steel is in the austenite structure and happily sitting at 1950F (eg). You want to get it to room temperature in sufficient time to start forming martensite. In most stainless steels that is a lot of time. The cooling rate should be continuous and preferably smooth. Placing in quench plates already speeds the rate vastly over an air quench. Why would we want to make it even faster. That just invites damage and warp. Many folks have formed an idea that the faster the quench the harder the steel gets...not so. If the steel misses the pearlite nose and continues in a continuous drop to Ms, then down to Mf...it will get as hard as it can.
Once the steel is below the Ms ( between 300F and 400F for most stainless steels) the rate can be even slower, within reason. The Mf for these type steels is around -100F, so the rate of drop in the plates is pretty insignificant.

The best way to assure full hardness is proper soak time and austenitization temperature...and for stainless and high alloy steels...cyro. Those things will make more difference than any other.
 
Great thanks!

So Stacy from what you wrote can infer that the air cooling between the plates I see some guys doing with their compressor hoses is not needed?

Does it have any benefit?

One thing I thought was that with the foil jackets the air might get more on one side of the blade than the other (if there is some space like on a distal taper or bevel) and induce the possibility of more warp.
 
Blowing air will speed the quench by a few percent max. Otherwise it just gives you something to do. Same goes with folks who make elaborate quench plates with circulating ice water in them.
When you read things in ASM specs like -"Air quench at XX atmospheres" or "Air quench in rapidly moving air", those are industrial processes for large pieces of steel. Such procedures are made unnecessary if using plates on a knife blade thickness piece of steel.

The amount of parallax and misalignment between two clamped plates and the blade is well within simple straightening limits. What gets prevented is major warp and twist. Foil or no foil, it isn't an issue.
 
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