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Ed Huntress
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Default Failure to get sharp

"RWL" wrote in message

One thing that I notice is that I never get a wire edge on the flat
side when grinding or hand sharpening these. That is probably a clue
to something.

It could be excessive hardness (unlikely, given your tempering method) or
excessive grain-coarsening. This is quite possible. More to follow.

To recount the process I used.
As best as I can tell, it's W-1 water hardening tool steel - my 1999
MSC catalog lists it only as flat ground tool steel. It's the same
composition as their drill rod which is listed as W-1.

Any water-hardening steel has enough hardening versatility that it will make
no difference at all which one it is, given your, home-shop
hardening methods. g

I heated the blank with a torch till it was red hot and it was no
longer attracted by a magnet.

Two points to consider here. Firstly, heat-hardening with a torch is very
tricky business. "Red hot" means different things to different people, under
different light, and in different moods and degrees of patience.

If you want to calibrate your eyeballs, take some cheap piece of plain,
high-carbon steel, cut it into four or five pieces, and heat each one to a
different degree of "red," immediately quenching it in water. Try your file
on them. The first one up the "red" scale toward yellow that puts up real
resistance to your file represents something close to 1400 deg. F. That's
your starting point.

If you don't do this, the only way to learn what "red hot" is, is to keep
making mistakes until you get it right. Don't rely entirely on your magnet.
The actual (as opposed to the theoretical) critical temperature is slightly
above the temperature at which most magnetism disappears.

The metal is relatively thin at 1/8 inch
thick, so I held it at this temp for no longer than an estimated 30
seconds to one minute.

It's very difficult to hold a consistent temperature that long with a torch.
But you don't have to. With steel that thin, as soon as it's the right red,
it's ready to quench.

Even a short period of holding it at an excessive temperature (an extremely
short period, if you go more than 200 deg. F or so over critical
temperature) can coarsen the grain. That will make the steel weak and
brittle, and can make it difficult to sharpen. There is nothing you can do
to fully correct this problem unless you anneal the steel, hot-work it, and
then re-heat-treat. Even then, you'd better know what you're doing, or you
won't get the grain-coarseness out.

After rapid quenching in water with a
stirring motion,...

Don't stir. Plunge. If you make a lot of blades, get a 5' piece of soft
copper tube, drill it full of small holes, squash one end flat, and (using a
plumbing adaptor), solder the other end to a hose fitting. Coil the copper
into a coil 3" in diameter and a foot or 18" long. Attach to garden hose,
or, if you're lucky, to the faucet on your laundry sink. Turn on water and
you'll have a great spray inside the coil. Plunge your heated blade into
that, and you'll get quick, even quenching.

I made mine in less than an hour.

I tempered in
a toaster oven. Since I don't have an oven thermometer I had to
guess the temp on the toaster oven was only close, and went on the low

A cheap oven thermometer will be worthwhile. Toaster ovens tend to run on
the cool side of nominal.

The second blank I tempered before grinding it to an angle. In this
run, the oven was set to 400 for 30 min, raised to 450 and held for
another 15 min. The blank never got the oxide color.

You oven is cool.

Has anyone had this experience?

As often as not. g I finally bought a dozen firebricks and I set them up
into a crude oven when I need to heat treat something like that. Two propane
torches supply the heat. I use the same bricks laid out flat to make a
take-down brazing/welding table.

Are they so hard that the edge is
breaking off or am I missing something else?

If you can't get the edge to curl, it may be too hard, or the grain may be
too coarse. Unfortunately, the test for either -- breaking the blade in a
vise -- produces a similar result either way, except that, with experience,
you'll be able to tell a blade that's grain-coarsened from one that's just
too hard by the way it breaks. But the latter shouldn't be a problem anyway,
because you'll see tempering colors as soon as you've reached a useful
tempering temperature.

I tried retempering the first blank with a fine tipped torch, playing
the flame over the back of the blade and keeping the sharp edge out of
the wash, but I still over did it. I got a dark straw oxide color on
the top of the blank, but the bottom, where it was resting on the fire
brick turned blue in areas. I tried sharpening this even though it
would be softer than ideal, but I can't say I noticed a whole lot of
difference. One end of the blade has gotten a little sharper than the
other end.

I suspect coarse grain. But that's not certain.

Soft steel often will take a very nice edge, if the grain is fine. It just
won't hold it.

Ed Huntress
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