in this week's episode I make a forum
tool and talk a little bit about
hardening steel in the home shop I have
a project coming up that I'd like to use
an OD radius cutter on normally I just
filed the radius in the lathe and cut
out a little paper gauge but I'm making
a number of these and I'd like to make
sure the radii are matching
I'll also be machining aluminium so
making a radius cutter isn't a big deal
Oh under w1 is the material I chose as a
compromise on machining hardened ability
in the home shop and durability
specifically in this case I'm using a 1
but why oh 1 or w1 why not d2 or 4140 or
some other tool steel why not machine an
annealed high speed steel blank can
harden it let's talk a little bit about
simple hardening procedures in the home
shop most of us are aware that many
types of Steel can be hardened in some
fashion and most of us understand the
basics of the hardening process heat up
the steel in some way and cool it from
the heated state very quickly I like
using sunflower oil but that depends on
which steel I'm hardening I like
sunflower oil for quenching because I
temper my parts in the home oven that
way it smells like I'm cooking something
not burning something and it keeps you
from getting into more trouble now
hardening steel is an entire field in
and of itself it's a process that
requires attention to details and it is
those little details that make it very
difficult to really master but if we
understand a few of the basics and make
a few careful choices we make the
process a little bit easier in the home
shop the most common method for heating
is the plumbers torch one of these or
maybe one of these I find these ones are
quite small and they don't do a very
good job you should look at one of these
or a turbo torch or something like that
these torches are usually propane fueled
and use atmospheric oxygen they're the
most common because they're the most
accessible and least expensive if you
have an oxy acetylene torch or an oxy
propane torch heating things up to
proper temperature are much quicker and
easier some folks also have temperature
controlled electric kilns that make the
heating process very controllable now if
you're really into hardening steel
consider looking into an oven they
aren't as difficult as they may appear
now if you're using a plumber's torch
and that's what I mainly use for
hardening small parts because it's quick
and inexpensive the limiting factor is
the amount of heat you can generate
these torches will only put out a
certain amount of BTUs it's not so much
the temperature of the flame a propane
flame is hot enough to reach the
transition temperature for most
hardening steels it's just that we
usually lose so much heat to the
surroundings to avoid losing heat you
could build a small Forge using fire
bricks like these ones here so back to
the original question yw1 or oh one tool
steel the most important factor is
carbon content double you want to know
one have about 0.9 5 percent carbon and
to understand why that's important let's
draw basics phase diagram for steel
so here's a basic diagram for steel
let's go through exactly what is on this
chart on the y-axis here we've plotted
temperature in Celsius along the x axis
we've plotted carbon content then there
are a bunch of lines desegregate the
graph in two different areas of phase or
Solutions of Steel if you will note we
aren't anywhere near the molten stage
yet Max is out here around 900 degrees
steel melts somewhere around 1400 or
1500 degrees Celsius up here near the
top in this triangle area if you will we
have a region called austenite in heat
treating that is the most important area
need to heat the steel up to its
austenite phase one interesting thing to
note about this austenite phase is that
it's non-magnetic you may have heard
that before
in this area here we have a mixture of
austenite and Fairey over in this area
here we have a mixture of austenite and
cementite and below this line at 727
degrees Celsius we have a mixture of
ferrite and cementite you'll also hear
words like pearlite used as well that
occurs below this line as well now the
names of all this stuff doesn't matter
all that much but the graph tells us
something very important in heat
treating steel our goal is something
called martensite a very hard structure
that is formed when an austenite is
quickly cooled it is this martensite
that transforms our machinable material
into something that can cut a non
hardened steel it's important to note in
the hardening process that we must
transform steel into its austenite phase
if we look at this graph we see a point
zero point seven seven percent carbon
where this transition temper is at its
lowest point fully austenite you can see
that here if we move to a lower carbon
content or a higher one the transition
temperature moves up as depicted by
these lines for those interested this
zero
seven seven percent carbon steel they
call that the eutectoid steel or
eutectoid point so steals like the to
tool steel have about 1.5 percent carbon
that's over here forty one forty Steel's
have boat 0.4 percent carbon that's over
here now if we draw those lines up
you'll see that in this case we actually
move off-camera somewhere around a
thousand degrees maybe just below a
thousand degrees and 4140 which would be
somewhere around here it's over here
which is above eight hundred degrees now
the alloying elements play with this
graph a fair bit this is really a
simplification but as you can see the
further you move away from the 0.77%
carbon content the higher the
temperature you need to get into this
austenite phase fully austenite phase
also when you move more to the left it
should be noted that steel really
doesn't have enough carbon to get fully
hard and these steels often carbon is
added in the hardening process through
various means so a1 and w1 have about
0.9 five percent carbon somewhere
between point nine nine point nine five
percent carbon they are some of the
lower carbon tool steels and as such
they have a lower temperature transition
point into austenite somewhere around
one draw line up here right above here
be a little bit here so somewhere
between 700 and 800 degrees celsius this
is why they are easier to harden using
home shop tools it's just easier to get
them into the fully austenite range for
proper hardening now let's look at how I
made the farm tool after drawing up what
I was looking for in Fusion I started
with a piece of round oh one tool steel
turned it down to size then drilled a
hole in the center to form the radius I
wanted to cut this hole was drilled on
an ankle to provide a relief for the
cutting tool
I then reamed the hole using an
inexpensive taper dream that left a bit
to be desired
after that it was milled to final shape
hardened honed and tested
[Music]