hi I'm James Hamilton from stuffing ups
woodworking Journal and this is the
biggest sharpening mistake a lot of
woodworkers make
so you've read a bunch of articles
you've watched all the YouTube videos
you spent hours with your sand paper
your water stones or whatever you use
and you just can't figure out why your
tools don't make those wispy thin
shavings that everyone else seems to be
getting the problem may be simple your
tools aren't sharp I know you've spent a
lot of time and they feel sharp it may
not be that you haven't spent enough
time on the bevels or that you're not
using fine enough grit the problem could
be that you're not paying proper
attention to the back of the tool many
woodworkers think that the shinier the
bevel of the tool the sharper it will be
but the bevel doesn't do the cutting the
cutting is done where the bevel meets
the back at that intersection where two
planes come together that's what matters
if you never pay attention to the back
of your tool you only do it half of the
job does that mean you have to double
your sharpening time spending as much
time on the back as you've been doing on
the front nope because a little time
spent on the back will also reduce the
amount of time you spend on the front
you won't be wearing away your bevels
wondering why your tool is not sharp
enough instead you'll be doing your
woodworking
first though it's important to
understand why the back must be flat
remember I said the cutting edge occurs
right at the edge where the two planes
meet it's easy enough to understand with
this little side profile drawing but a
chisel is a three dimensional object if
you take a head-on view the potential
problems come into focus if the back of
the chisel has a concave or hollow
surface then parts of the edge will be
sharp and in contact with the wood when
you use it but not other parts likewise
if the back is bellied or convex then
that portion of the edge will be able to
cut wood but the rest won't so the back
of the tool is just as important as the
bevel tool makers have understood this
for as long as there have been tools and
it used to affect the way they made them
when a piece of tool steel is heat
treated it almost always warps one side
ends up belied and the other side hollow
in the old days a Western tool maker
would wait to grind his bevel until
after it was heat treated then he would
take a look at that piece of steel he
would find the bellied side and that is
where he would grind his
level so that the back side would be the
hollow one Japanese toolmakers would
take it a step further they would
intentionally Forge a deep Hollow in the
back side of their chisels and hand
plain irons but wait a minute if a
hollow back is a bad thing
why would tool makers do it
intentionally because they know the heat
treating process is going to warp the
tool and the only way to get it flat
again would be to grind it and polish it
in modern times they've shifted that
responsibility to you along with a
little bit of cost savings but if you're
gonna save a few bucks by flattening the
back yourself you'd better hope that
your manufacturer gave you one that has
a hollow back instead of a belly because
the more belly there is on the back the
more steel has to be removed to get it
flat now let's look at a real world
example if you took a new chisel and you
rub it on a stone you'll quickly see
what you're dealing with the high parts
of the steel will be shiny the low parts
will be dull or vice versa depending how
the lights hitting it to get it flat
you're gonna have to wear away all those
shiny areas and tell the dull areas come
in contact with the stone too and they
become shiny this can be a bit of a
crapshoot with many tools one chisel in
a set may require just a little bit of
work it might be mostly flat right out
of the package while another tool and
that exact same set may require a ton of
work the most difficult chisels are
those that have a full bellied back you
know how hard it is to get rid of a
belly and what the tool that means a lot
of Steel removal to get rid of what
amounts to a hump in the center those
cases are more common these days sadly
because manufacturers are grinding their
bevels before the heat treating process
when the steel is softer and easier for
them to work when they finally get
around to heat treating it and it
inevitably warps well now you've got a
50% chance that that belly is gonna end
up on the back where you've got to deal
with it instead of on the front where it
really doesn't matter only the finest
chisels are flat enough for use right
out of the package even though most
manufacturers do try to grind it flat a
little bit these family sweetheart
chisels which I really like weren't flat
when they were new I had to do a fair
amount of work to get them there but
you'll notice that I didn't flatten the
entire back
you can even see the grinder marks left
by the manufacturer on most of it and
what I did work it
they aren't perfectly smooth and shiny
it might look so on camera but there's
some scratches in there this leads us to
two important questions first does the
back have to be perfectly shiny and
polished like a mirror as well as flat
and second how much of the back has to
be flat let's start with the shiny part
the whole point of polishing is to
remove the deep scratches that create a
serrated edge because a serrated or
toothed the edge won't cut as well it
won't leave as fine a surface behind and
it won't last as long between sharpening
it doesn't matter if those scratches are
on the front beveled side or on the back
if they touch the edge where those two
planes meet at the intersection the
effects gonna be the same if those
scratches are really shallow really fine
then the effects gonna be minimal it's
fine if one or two deep scratches are
there but not a ton of them that's not a
big deal either as long as they aren't
so deep that they're leaving grooves or
ridges in your workpiece as you work
though with the tool but a lot of deep
scratches left behind by a coarse stone
that's a bad thing there's a reason
people shave with a razor and not a
bread knife how course is too coarse is
the subject for another video which you
already made I'll put a link to in the
notes below this one my point is your
edge is only as fine as the coarsest
of the two planes that make it up if you
get perfectly polished on your bevel but
you got tons of deep scratches on your
back well you waste your time on your
bevel now if the important part of the
edge is the point where the two planes
meet does the rest of the toll really
matter
do I have to flatten the entire back or
just the part right next to the edge
technically you only have to flatten
sharpen and polish the thin strip of
Steel on either side of that
intersection one on each plane the rest
of the back or even the rest of the
bevel for that matter has no effect on
sharpness and that little tidbit of
information is what makes the ruler
trick possible the ruler trick is a way
to flatten the back of a hand plane iron
in seconds instead of hours
I'm not sure if it was practice much in
the old timey days but modern
woodworkers credit David Charles worth
with its development it's pretty simple
instead of wearing down the entire back
of this plain iron which might have a
great big belly on it and so it could
take ages to get it all flat why not
place a thin metal ruler on a stone and
use it to lift the plain iron at a very
slight angle so that the work is
concentrated on the very edge where it
counts the effect is an almost
imperceptible back bevel it looks shiny
to the eye but it's actually a slight
bevel and that creates a new perfectly
flat plane although a very narrow one to
intersect with the bevel on the front it
works try if you need a ruler I'll link
to a couple inexpensive ones in the
notes below but really anything about
1/32 of an inch thick will work just
fine there are two downsides to a ruler
trick though first you have to repeat it
every time or two you sharpen your plane
iron as your edge dulls and rounds over
and then you go back to your stone or
whatever and you sharpen it you are
slightly shortening the tool it doesn't
take much time before you've removed
that fine back beveled portion so you
have to get your ruler back out and
restore it really you're flattening the
back but you're doing it incrementally
one thin strip at a time every time or
two you sharpen and that ends up being a
lot less tedious than sitting for an
hour or more in flattening the entire
back of a bellied or badly hollowed
plain iron the second downside to the
ruler trick and perhaps its most
significant is you cannot use it with
chisels well you can if you want I do
some of my chisels with back bevels
because I don't want to flatten them but
that back bevel limits the functionality
of the tool I can still chop with it I
can even do some trimming if I hold it
at an angle but I can't do anything with
my chisel that requires using the back
as a reference such as paring one
surface flush with another or using a
guide block to keep the chisel
perpendicular when paring dovetails in
cases like that
the back of the chisel may look like
it's fully in contact with the wood but
that fine back bevel
lifts the cutting edge slightly up and
it's not gonna cut since many new
woodworkers only have one set of chisels
they use for everything then I'd say
don't use the ruler trick at all if
you're going to use it use it only on
chisels that you're going to be chopping
with not ones that you're going to be
pairing with in those cases you're just
gonna have to take the time to flatten
it by hand do you have to flatten the
whole thing though no I tried to hold it
flat on the stone as I work it but I'm
only worrying about flattening the last
inch three quarters of an inch or so
that is the reference surface that you
need and that will give you all you need
to have a nice sharp chisel of course
you can't make a tool flat if your
sharpening surface isn't flat as well
and this is another cause of frustration
for many woodworkers you if you rub a
tool on a dish surface your edge will
come out shaped like that surface so
you're effectively giving your edge a
hollow or a belly to shape if you strip
with sandpaper then you're gonna have to
use some tempered glass or some granite
or something you know is perfectly flat
underneath it if you use water stones
you have to maintain them regularly a
lot of people do it after every
sharpening they reflect on their stone
that's why for hand sharpening I prefer
to use Diamond stones because they stay
flat without maintenance I like the
trend stones because they make sure that
the solid steel substrate they're not
laminated is perfectly flat within a
half a thousandth of an inch from end to
end that's twice as flat as the
standards used by everybody else we made
a video about Diamond stones a while
back I'll put a link to it in the notes
below this video if you're interested we
also made another video about whatever
sharpening medium you're using sandpaper
stones pace whatever about the different
grits that you should use and how sharp
is just sharp enough I'll link to that
too just click on show more if you're on
youtube next time we do a sharpening
video we're gonna talk about leather
straps an ancient sharpening tool that
can give you big results for more great
tips tricks and tutorials designed to
make you a better woodworker check out
stumpy nubs woodworking journal you can
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