The Super Scraper
June 2000
My students, colleagues and I are always thinking
or hearing about tools we’d like to see. Some of them are real tools
that do some job better than the ones we're used to; some are better
or cheaper editions of old favorites and some are purely wishful thinking
and will never exist in the real world. This page is a showcase for
all of them, real or imaginary. It is left as an exercise for the viewer
to distinguish between them, although I will try to identify the imaginary
tools with the ACME label:
I am not, nor do I intend to become, a supplier
of lutherie tools. If I know a source for a tool, I will try to include
the information and links.
In Il Segreti di Stradivari Simone Sacconni
wrote (p 46) : ... scrapers were made from blades of sabers. Since
they were of very hard steel one could not turn the edge and therefore
they were used like a knife. When I began working with Carleen
Hutchins she used such a scraper, and I have finally made some for myself.
This is, in my estimation, the best possible scraper for builders of
arched instruments.
It works on the same principle as scraping with a
broken piece of glass; a common technique among carpenters. A very hard
material can take an exceedingly keen edge and when it is perpendicular,
as it is in broken glass, it can last for a long time even if the material
is brittle. This tool has the advantage over glass of having a shape
that is well defined and re-sharpenable.
The scraper shown above was made from a power hacksaw
blade. My students and I have made several out of O-1 oil
hardening tool steel. The thickness should be 3/32" or a little
more. I find it easiest to rough shape the tool with a file before hardening
it. It is heated (O-1 steel requires about 1450° F) and quenched
to bring it to full hardness. This will normally cause some warpage.
I have hollow ground the surfaces of mine to facilitate leveling the
edge. Do not anneal or temper it to remove the warp as it will reduce
the keenness and edge holding ability. Once the surface can be polished
level all the way around the scraper it can be sharpened.
I find it easiest to hollow grind the edge perpendicular
to the centerline of the scraper:
Simply set the tool rest on your grinder perpendicular
to the wheel and grind all around. Use as fine a wheel as possible and
don't apply too much pressure. If desired, the edge can be further dressed
on a fine stone with or without a guide block.
In use, this scraper will give an extremely smooth
cut even on soft or highly figured wood. It has little tendency to chatter
due to it's weight and does not heat up. It is much easier on the thumbs
than a normal scraper as it is not sprung in
use. To re-sharpen simply lap the surface on a fine stone and re-grind
the edge.
The scraper shown was sharpened after the ASIA Symposium
in March and retained a usable edge for two months. It took less then
two minutes to re-sharpen. My kind of tool!
At present there is no source I know of for this
type of scraper, but one of the major lutherie tool suppliers has expressed
an interest in making them. If they do, I'm sure they will let you know
through their ubiquitous catalog.
|