"Arfa Daily" wrote in message
news:fkdTn.96339$oi7.64378@hurricane...


"Spamlet" wrote in message
...

"Arfa Daily" wrote in message
...
Many years ago, my brother in law, who was a mechanical engineer
/
toolmaker, gave me a bag of 'case hardening powder', which I
still have.
Does anyone know what exactly this stuff is (it's white, and if
the
police got hold of it, I'd probably be locked up whilst they
determined
just what it was ...) and how to use it ? I got to thinking about
it
today, when I was stoning the edge on a chisel ready for use
tomorrow on
a job. It occurred to me that once the original factory edge has
gone
from a wood chisel or plane blade or whatever, and you've
resharpened it,
it never seems to last as long again as it originally did. Is
this
because they harden the edge when it's made ? Is it appropriate,
or even
possible with home DIY facilities, to harden the edge once it's
been
restored ?

Arfa


It's quite amusing reading some of the comments about secret
recipes of
potions and powders for case hardening, and for hardening and
annealing/tempering metals. Whilst not being by any means an
expert - big
subject - I worked testing metals in a lab for a while, and
actually had
to measure thickness of the case hardening on mild steel strip: we
cut the
strip into randomly selected small sections, then encapsulated
them in
perspex cylinders with a nifty hot press (also handy for making
souvenir
coin etc key fobs) cut it in sections; polished to mirror finish;
etch in
conc HCl or similar, and then inspect under microscope and measure
dark
edge. Also had to try and measure hardness across the strips
too -
measuring the diagonals of a square produced by diamond with
weights
attached. Pain in the neck actually, and hard statistical work in
the
days when a calculator was a curiosity only affordable by devoted
Sinclair
fans... ah the little red lights... memories...

Anyhow, secret white powder you can all use next time to make a
big hole
in a wall and don't want to pay out for a drill you only use once?
You
have it by the kilo and it begins with S and ends in r. You got
it. I'm
surprised nobody has mentioned the trick for putting water pipes
through
walls: probably all spoiled rotten by power tools! Standard piece
of iron
water pipe - prob should wear mask as often lead lined: cut a
jagged end
of rough teeth on a length long enough to go through wall;
blowlamp on end
with said teeth till red hot - or hot as it gets before the gas
runs out;
dunk straight into pot of sugar, Lots of candyfloss smells and
smoke and
flames, so not to be done near your petrol cans or old newspapers!
Actually any suitably coating carbon source will do, and old
engine oil
was also favoured by some, but sugar works fine and I generally
have a pot
of it in the garage for odd bits and pieces that want toughening.
At a
pinch you can even make your own springs...

I found that a dunk or two in the sugar bowl enabled me to bore
through a
cavity brick wall fairly neatly with the hammer and turn method
similarly
used with the old rawplug tools. Probably not quite as neat as
modern
drills, but such things were way beyond the pockets of mere
mortals once
upon a time, before those wonderful Chinese people caught the
capitalist
bug.

As for sharpening chisels and plane blades, it is quite hard to
hold them
at the 25 or 30 degrees positions by hand (and for drills very
mindboggling, but you can get an eye for the angles in the end),
but I
have a very handy little clamp on a roller made by Eclipse, that
you clamp
your chisel or plane blade in; make sure the correct length is
projecting
for the angle in question, and then you roll it up and down your
series of
oil stones until all is razor sharp and satisfactory. Always
start any
job with sharpening the chisels and plane blades: satisfying and
saves on
lengthy once in a blue moon regrinds.

And while we are on blue. The hardness and temper of steels is of
course
ultimately dependent on their composition: some can be so hard it
is
difficult to find anything to cut them with once they have been
heat
treated (skilled metallurgists can get a good idea of the
composition/hardness by looking at the colour of the sparks as
they grind:
not me). When grinding with a grindwheel always have a pot of
water handy
and keep dunking. For heftyish things like cold chisels dunk well
before
your fingers get hot or you will make the end so brittle it just
snaps off
when you hit the other end. With screwdrivers it's even more
fussy as
they heat up very quickly and are easily ruined, and will either
snap as
soon as you turn them, or twist like cheese (if it was only a
cheap case
hardened one). There are tables of temper colours for different
purposes
'straw' coloured tending to be harder than 'blue' for example -
but again
varying with the metal. Straw just at the tip, for cold chisels,
and
grading into blue behind, to give a little bounce rather than
snap...

Another v interesting subject...

S


Indeed, and I've learnt a lot - thanks all. The particular chisel in
question was only a DIY shop 'cheapo'. I have sharpened it
regularly, but
only ever on a coarse / fine two sided oilstone, so not been
overheated on a
wheel. I wouldn't say that I am 'artisan skilled' at blade
sharpening, but
we were taught it at school in the woodworking classes many many
moons ago,
and I think that I am pretty fair at getting a good edge at about
the right
angle. My test for a good edge is to see if it will cut a piece of
bent
paper across its whole width. If it does, that seems to me to be a
good
enough edge for construction level woodworking. Cabinet making might
be a
different story, but this chisel is usually just used for things
like lap
joints on soft pine.

From what's been said, it is probably either just my imagination, or
my lack
of skill at precision sharpening, that makes it seem like the edge
doesn't
last as long as when it was new. I just assumed that being a
cheapie, it was
made from a low quality steel, and had just had its edge hardened
originally, and that over time, I had stoned that away. I'll be
doing a fair
amount of chopping out with it today, so be interesting to see how
it holds
up.

Arfa


If it's a real cheap cheapy it's entirely possible it was case
hardened back where it was born in China. There is a shipment of nasty
Chinese hack saw blades lurking in the small shops / boot fairs that
cease cutting after the first few strokes as the case is very very
thin!

AWEM