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Learn How. Discover Why. Build Better. - Christopher Schwarz
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Rotary Lapping Machines
by Christopher Schwarz
Copyright
2007. Originally appeared in the
Fine
Tool Journal |
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1 of 4
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A surprising advancement in making hand tools
ready to work right out of the box.
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While
many users are wowed by the fact that the Bridge
City VP60 plane has a variable-pitch frog, what also
is impressive is the iron itself. It’s lapped
to an optical flat finish. In other words:
Take the tool out of the box, sharpen the bevel,
chase the burr off the back. Go to work.
No lapping of the face of the iron is necessary.
In fact, you will only scratch up the perfect mirror
on the face. |
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One of the
first rules in setting up hand tools (and in
medicine, I think) is this: First, do no harm.
But this is also one of the first rules to be broken
because of ignorance, ham-handedness or just bad
luck. I’ve
taught a fair number of people to sharpen their edge tools
during the last 13 years, and I see the same problems among most
beginners. They don’t know what “sharp” really is.
And they don’t know how to get to “sharp.” And so they do all
the activities that resemble sharpening – it’s a bit like seeing
the monkeys imitate the visitors at the zoo.
They rub both sides of the tool (the bevel and the flat side) on
the stones vigorously. They examine their progress (sometimes
after hours of work). The result is that most edges from
beginners look like they have been sharpened by, well, a monkey. |
Of course, I should
talk, my first edges looked just as bad. But that’s little
consolation when I tell that story to a beginning sharpener who
has just ruined a perfectly fine steel tool.
The problem is, in part,
technique. But the other part of the problem is in the manufacture
of modern edge tools. Knowledge of metallurgy and heat-treating has
been discarded by some manufacturers. As a result, some new tools
can be almost impossible to sharpen.
Not only did Lee
Valley lap the face of the iron, but employees also lapped
the sole of the tool. The result is a little block plane that is
made in Canada,
costs less than a bottle of whisky and performs like a tool that
costs as much
as a bottle of single-malt scotch.
Now I
know I will take some grief for that statement, but I have set up
hundreds and hundreds of new and vintage edge tools as an editor at
Popular Woodworking magazine. Not a week goes by that someone
doesn’t send me something for evaluation that has to be sharpened,
set up and used. I have lapped more brand new chisel backs
than I care to remember.
The defect I find in edge
tools is related to the problem I see beginners struggle with, and
that’s in truing up the unbeveled surface of an edge tool, which is
sometimes called the face or the back of the tool. (For this
article, I’ll call the bevel the bevel and the unbeveled side the
face.)
So it’s the face that’s
messed up. The steel is bowed or twisted into such a banana shape
that it would take hours (perhaps days) to true up the edge enough
to actually sharpen the darn thing.
