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RWL
 
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Default Failure to get sharp


This is a follow on to my progress in making some blades out of water
hardening tool steel.

The blades have been ground to an angle of 20
BUT they don't feel or act sharp, unlike a commercial blade or a
similarly ground blades on a wood plane. The question is why won't
they TAKE an edge (as opposed to why won't they hold an edge)

I've looked at them under a magnifying glass and can't see anything
odd or different than a similar commercial blade I'm using as my
model. The edge is coming to a point.

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.

Having never hardened and tempered a tool before, I'm wondering if I
did something wrong.

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.
I heated the blank with a torch till it was red hot and it was no
longer attracted by a magnet. 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. After rapid quenching in water with a
stirring motion, a file would no longer cut the steel. 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
side.

The first blank was ground to its intended angle BEFORE tempering. I
gournd slowly and no oxide colors developed on the blade edge as I was
grinding. I heated it for 30 min at about 450. I could see the
faintest of yellow oxide color on the blank. I finished by hand
stoning the edge using a variety of methods - diamond, different
grades of emory glued to thick glass. It's sort of sharp - but like a
dull plane blade. It just won't get sharp.

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. When ground
this one doesn't take an edge either, and doesn't feel quite as
"sharp" as the first one.

Has anyone had this experience? Are they so hard that the edge is
breaking off or am I missing something else?

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.

RWL

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