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271371 "yorkshireman@y..." <yorkshireman@y...> 2020‑07‑04 Re: tapered plane irons (warning -ramble mode)
Tut tut.  Don asked a perfectly intriguing question last month, and it’s taken
Adam to point out that we hadn’t replied.

So here is my tuppence worth - and worth every penny.  

Two penies are, of course, traditional to place over the eyes of the dead, but
don’t let that get in the way (Lockdown viewing of the newest BBC version of
‘Christmas Carol’ brought that to mind.

But back to the question - what angle to grind a blade?  

and the ultimate answer is - ‘It depends’ 

No one here would expect anything else, surely.  Don has a good question though,
so let’s see what the dependencies are.  In diminishing order of importance they
are:-

The tool  
The timber  
The user.  

Firstly - the bed angle of the tool.  

There are only 2 was of mounting a blade.  Bevel down -as in a bench plane, or
bevel up, as in some bench planes and block planes, and chisels.

At different times, manufacturers have experimented with bed angles.  A few
hundred years of experience has settled on 45 degrees being a suitable
compromise.  York pitch is taken as being 50 degrees.  The fact that York is the
capital of Yorkshire, has nothing to do with my liking for the name and number.
Half pitch is 60 degrees.

Begin by assuming there is no angle on the blade at all.  For a bevel down
blade, If the bed angle of the plane is 45 degrees, then the effective angle of
the blade meeting the wood will also be 45.  You will need a 45 degree on the
trailing side to make the leading edge of the blade contact the timber.  This is
the bevel.  Make it a bit less than 45 to give some clearance, otherwise the
leading corner - the sharp bit - is not in contact with the wood.  In this
configuration of blade, the angle the blade meets the timber is always
determined by the bed angle.

So, lets say 40 degrees, giving an effective angle of 5 degrees of clearance. 

Alternatively, we know that a slicing cut, as in a chisel or carving knife, is
more effective with a lower angle, so if we use a plane with a lower bed angle,
we will have better, or at least different, results.  A 62 (Low angle jack
plane, Jeff)  has a bed angle of 12 degrees.   Imagine the blade as a slab
again, and it meets at 12 degrees, This is a bevel up plane, so the effective
angle is 12 degrees,  no clearance bevel needed,  But some sort of bevel is
needed to produce a sharp edge.  A 25 degree bevel, plus the bed, will provide a
37 degree angle.

Now comes your compromising.  Does 37 degrees, in your timber, provide the
balance you want between effort and finish?

If you put no bevel on, then you would find it hard to make a cut.  if you put a
bevel of 80 degrees,  being 92 degrees angle of attack, the chips wouldn’t break
away cleanly and immediately, and you would get a rough finish.  (Also, the edge
is now so thin that it is weak and unsupported.  Once again, we can use millions
of hours of other people’s experience that turns out to settle on a combined
angle of around that 45 degrees being a good all round figure.

Now turn to timber - what sort of work do you do?  If you are working with
hardwoods then a steeper bevel is generally good.  The higher pitch of planes -
York and cabinet pitches that bring the angle up to 50 or 60 degrees are used
for hard woods that may be tricky.  At the final end of this spectrum we come to
scrapers, where the angle of attack is 90 degrees or more, with very light cuts
to deal with problem grain.   A cabinet pitch plane is something that lets you
plane such a timber and still tries to minimise tear out.

The other consideration for hard woods is blade wear.  A steeper bevel leaves
more material behind the cutting edge to provide some strength and rigidity.
But it is harder to force through the timber.
Now, if you are working softwoods, it’s all different.  You can use a shallower
pitch, and a finer bevel, that original 45 degree pitch of bazillions of Stanley
planes from the days of wooden buildings all done by hand slews ‘the average’
towards the big seller items and the bench planes are made for soft woods.  In
paces where hard woods were in use, which in out tradition is probably finer
cabinet work, with the introduction of mahogany, walnut even the earlier oak,
then the norm would be for something like York pitch, and a bevel that is
steeper.

Your plane - your timber - your sharpening methods - your muscle power. 


So, as I said at the beginning  “It depends”  

The only real advice I would give, and do so to any newcomers, is not to be
obsessive.  You really MUST find out how to sharpen to as near to that obsidian
one atom thickness edge.  When you’ve done that, ignore it most of the time,
just sharpen ‘enough’ to get the job done, and keep a few spare planes set up
for different timber (on this list that should be no problem), and one with that
super sharp blade that is set to take a mere kiss of wispiness at a time for the
final clean up.


Hope all that helped.  

Richard Wilson
Yorkshireman Galoot.  In Northumbria

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