"RWL" wrote in message
...

Follow up to some previous inquiries I made recently and more
questions.

The tool is a 3/4 x 1/8 x 2" long piece of W-1 water hardening tool
steel. It's bevelled along one of the long sides like a short planer
knife and it must be razor sharp.

Heated with Prestolite acetylene torch, quenched in water, temepred to
light straw at 500º in a toaster oven. [Yes, you can achieve this
temperature in a toaster oven. I got an oven thermometer and checked.
Leaving it in for 20 min gives a light yellow temper. 40 min. gives a
dark straw temper.]

That's an excellent way to draw the part!

They warped a little after hardening and tempering. Is this just
something you have to live with or are there home shop tricks that
prevent this?

I think you're experiencing the release of stress in the material by
removing stock unevenly, a function of the bevel of which you spoke. If
you have many of these to do, you may find that quenching them on a very
small angle as they enter the water could cool the front side (with the
bevel, which I'm sure is the crowned side) every so slightly faster than the
back side, adding the small amount of stress necessary to hold the part
straight. I'm sure you can see that could be difficult. How you
introduce the part to your quenching media is critical. If you drop them in
flat side first, they will warp terribly, so a slight modification of the
process could yield a lot of variables.

It's not that the warp is bad, but it takes a LOT of
grinding / honing to get the blade flat after it's hardened and
tempered. I didn't measure the warp, but my guess is that it's less
than 0.010" longitudinally.

Not really all that bad, considering, but it sure as hell is irritating,
isn't it?

The 6" belt on my belt sander shined up the bottom nicely, but it
certainly doesn't remove metal very fast. The belt was the standard
one that came on this Grizzly sander. Are there belts specifically
intended for metal grinding that will do a faster job?

I've not used the new blue belts (their composition evades me at the moment,
but I think they're boron carbide), but they are much better suited to metal
removal than the older style belts. One thing of which to be certain is
that your belt is not silicon carbide, which is not suited to grinding
steel. An aluminum oxide belt will do a much better job and create a lot
less heat. Silicon carbide dissolves into the steel, dulling the grain
almost instantly, thus it doesn't cut, and creates lots of heat just
rubbing.

Is Water hardening tool steel is more prone to warping than oil
hardening?

To my knowledge, no. You could, however, try using an air hardening
steel, which will circumvent the rapid cooling. These steels are well
known for their stability. You would likely have to use a small furnace in
place of the torch, though. The torch itself can be the source of the
warping due to uneven heating.

Observation - It's a lot easier to put a bevel for sharpening on the
tool steel with a milling machine before it's hard than grinding the
bevel afterwards, even if it has been tempered.

That is true when working as you do, but you could grind the bevel with a
surface grinder rather easily, although the stress that causes the piece to
warp would still be a factor. If I had the job to do, I'd rough the parts,
heat treat, then grind all over. You are almost guaranteed a part flat
within less than .0002" if you're much of a grinder.

Another observation - you can't "spring" a blade that's been tempered
at 500º back to flat. It breaks first. Boy was that interesting.
The shop isn't really dim, but when that broke, there was a small
flash of light at the break!

Yep, lots of energy released when you break something that has the high
tensile strength of heat treated tool steels. Dangerous, too. Pieces have
been known to take out eyes and any other soft tissue. Heat treated items
do not lend themselves to bending unless they are drawn well down, and then
it can be difficult.

Harold