One
of the most important skills a woodworker can acquire is the ability
to sharpen tools easily and well. Working with hand tools can be
a frustrating experience unless you have sharp tools. The goal of
this lesson is, with a mimimum of equipment, is for you to be able
to produce razor sharp cutting edges on any tool blade consistently.
This
lesson focuses on honing. It was written by Maurice Fraser and is
based on material and techniques taught in his classes at the Craft
Students League in New York City. Maurice has been teaching
woodworking for over 25 years and was a frequent contributor to
Fine Woodworking magazine in additon to many other publications.
Editing and additional material on the history of sharpening was
provided by Bob Mathison, Curator of the Museum.
There are three
areas of expertise in sharpening:
- The
mechanics of what is a sharp edge.
- The
particular technology of abrasives and the sequence in which they
are used.
- The
technique of holding the tool so that a uniform edge that can
be created and maintained with a minimum of effort.
What
are sharp tools
We
could describe a sharp tool as one you can shave with. This doesn't
mean that unless a tool is sharp enough to shave with it's useless,
or that you should be shaving with your tools, but it does give
a frame of reference that is easy to understand. However, for the
purposes of teaching sharpening we can come up with a less subjective
description.
The
cutting edge of a chisel looks, in cross section, like the
apex of a long triangle. Although the meeting of the back
and the ground bevel (at the end of a 25 deg taper) looks
like a triangle, it does not taper to infinity. The edge is
of finite but very small thickness - just a few microns across.
If the edge is thick enough to reflect even a cobweb-thin
line of light, it is dull for woodworking purposes. If there
is no glint on/along the edge, then it is presumed sharp.
|
|
|
|
Edge
tools ought to be sold sharp, but they rarely if ever are today.
It is not practical to reduce substantial thickness by honing
(rubbing on a whetstone). In the Western tradition, grinding
(on the edge surface of a rotating abrasive wheel) does this.
This is fast and effective. However, grinding to sharpness does
not produce an edge that is ready to use. A ground edge has
two flaws that must be removed by honing: 1. Coarse edge texture.
2. Burr. And there are additional reasons to hone. See the following
section, "The 4 Reasons for Honing." |
Why
Sharpening Guides Make it Harder
The
most important thing you can come away with from this lesson is
the technique for holding and moving a tool on a stone. Most sharpening
lessons deal with the technology and sharpening sequence and leave
this part out. But free holding a tool consistently and easily is
the key to sharpening easily and well. It's not that difficult at
all. There are a tremendous number of products on the market designed
to hold a blade at a consistent angle to a honing stone. However,
almost all of them share two important flaws: The jigs allow you
to repeat a motion but always in the same part of the stone. For
waterstones this means the stones will wear in certain spots faster
and require more maintenance. The second problem with honing guides
is more subtle: The first time you sharpen you establish some sort
of bevel. The second time you sharpen you need to maintain the same
exact bevel; The important word here is "exact"; If it's not exact,
you tend to create a secondary and then tertiary bevel at each attempt
at sharpening. This makes for much more work. Even if you can get
really, really close to getting the same bevel, setting a tool in
a jig exactly is tedious and very hard to get perfect. And it takes
time. You'll find it a great pleasure to be able to just take a
tool and immediately put it onto a stone without having to worry
about setting up a jig.
Jigs
and guides do have a place. We do use jigs for holding tools when
we grind them and for really rough honing where a grinder is not
available and we have to remove a lot of metal using a coarse stone.
And we sell all sorts of jigs in our Museum Store. Therefore please
realize we are not trying to present a "religious" argument but
simply trying to show you how we make it easier. An argument made
against hand tools is that it's hard to make them work. A hundred
years ago and more, people made hand tools work. They had no choice:
they didn't have power tools. Woodworkers were able to be productive
by having the right tool and developing the skill to maintain and
use it properly. If you can duplicate that skill, you can be just
as productive.
|