The following article by Albert W. Fischer originally appeared in the August 1996, issue of our Bulletin.
Al Fischer was an engineer for General Motors where he worked directly with another ingenious engineer: none other than Charles Kettering. Al's retired now and lives in La Jolla, California. He's been an amateur violin maker since 1939.
Al has been a SCAVM member since January of 1968. He was president of the Association during 1970. He is a regular contributor to our Bulletin and is the designer of numerous ingenious jigs and fixtures useful in instrument making. He is well known for the application of power tools to the art, but is very adept in the application of hand tools as well.
Your editor, Leonard Showalter, wasn’t able to attend the August meeting of SCAVM. He asked me to write the highlights of the meeting for the benefit of the members who were unable to attend. The meeting consisted of a presentation on how to easily make variously shaped palm gouges that are ideal for carving the scroll and also useful in other areas of the violin. A display of twelve various palm gouges in its own convenient hinged box (see illustration) was available for the members to examine.
When I carved my first scroll some years ago, I found it was more
convenient to carve the helix on the scroll by holding the neck
in my left hand and carving with a gouge held in my right hand.
The gouges I had at that time were beautiful conventional gouges
made of polished English Sheffield steel about 7½ inches
long. To control the accuracy of the cut, I found I was holding
the blade with my fingers close to the cutting edge and my palm
barely touched the handle. This allowed me to easily rotate the
scroll and always have the cutting operation on top where it is
easily seen, but the pushing had to be done with the fingers which,
after a while, tired from holding the blade. I thought this method
of carving was unconventional until I witnessed—on Public
TV—a woodcarver from Oberammergau hand carving a small wood
statue. He was holding the statue in his left hand and carving
the detail with a long gouge held in his right hand. You guessed
it. He held the blade with his fingers close to the cutting edge.
The thought then occurred to me: why not make short gouges where
the handle will fit in the palm of one’s hand and be more
comfortable to use?
I guess there were palm gouges available at the time for the model
maker, but they were hand forged from solid carbon steel and expensive
if one were buying a dozen different shapes. Some of the sizes
I wanted were not even available. I had some old dull hacksaw
blades in a drawer for some reason, and maybe this was the reason.
I felt they would make good palm gouges, and they did.
The gouges I made are shown in Fig. 1. The simple forming tools
used are shown in Fig. 2. The metallurgy of working high carbon
steel is shown on the chart in Fig 3. The chart shown at the meeting
was in color and I regret we cannot show it in color here.
To begin, the blade is made of high carbon steel having 1% or
more carbon. Hacksaw blades and clockspring meet this requirement.
Some hacksaw blades are made of high speed steel or alloyed in
other ways, so avoid these. The heat treatment is more complicated
and I feel the cutting edge is not as good for wood as high carbon
steel. If the sparks are few, and a dull red in color, the material
is not high carbon steel, so do not attempt to use it. A good
alternate material for making the gouges is blued clockspring.
San Diego Hardware has a good selection of coils of various widths
and thicknesses and they will cut off any length you want. I like
it because of the choice of sizes and the edges are already nicely
rounded. No teeth to file off. Whether you use hacksaw blades
or clockspring, the material will have to be annealed to soften
the metal for forming the blades without cracking. This can be
done with an ordinary propane torch by slowly heating it all over
to a dull red color. Annealing does not happen in an instant.
The longer you heat it to a red color the better. Think of it
as an ice cube melting in a pan of water. It doesn’t melt
instantly, and so it is with high carbon steel when changing from
martensite carbon (hard) to pearlite carbon (soft). See Fig. 3.
The flat part of the curve shows the time element required for
the change to occur. I found it easier to anneal the strips if
precut to 3-inch lengths. Mark the strip with a carbide scribe
where you want the cut to be made and just anneal those areas.
You can now cut that point with tin snips. Hold the 3-inch strip
at one end with an old needle nose pliers or a pair of tongs and
slowly heat to a dull red all over. Reverse ends to be sure to
anneal the end held by the pliers. Place against something noninflammable
and allow to cool in air to room temperature. Do not quench or
cool in water.
Fig. 2 shows the simple tools used to form the blade. Most hardware stores have HANDI-METAL in various sizes—one being ½" square by 12 inches long. Cut this bar in half lengthwise and clamp the two halves together so a series of holes from 3/16" dia. to 7/16" dia. can be drilled in the drill press. The holes should be drilled exactly on the split line, so use the method shown in Fig. 2 to insure accuracy. After drilling, realign the two halves as shown and bolt or rivet together. Clamp some suitable pins in place for alignment when drilling the rivet holes so you will have a continuous groove without a step. Since the gouge stock is approximately 1/32" thick, you will need forming pins about 4 inches long and 1/16" smaller in diameter than the diameter of the grooves. These can be long nails, bolts, rods, or whatever is available in your shop. I keep an assortment of drill rod handy and it is ideal for this purpose. It is a good idea to grind a small flat where you will strike the rod with a hammer to avoid getting hammer marks all around the rod. To do the forming you will need a heavy hammer such as a machinist’s hammer and some heavy metal object to pound on. A heavy machinist’s vise will also do. I use a small anvil made from a 12-inch section of railroad track.
Start the forming of the blade by placing one of the annealed
blades across the 7/16" dia. slot with a 3/8" dia. rod
on top. Give the pin a smart blow with the heavy hammer and continue
with the next inch until the entire length is partially formed.
Repeat this operation until the entire length has a uniform 3/16-inch
radius inside.
At this stage a decision must be made as to the radius desired
on the cutting edge of the blade. If it is a 3/16-inch radius,
leave the blade as is and continue forming the 1-inch long tang.
Reduce the tang radius first with a 5/16" dia. pin in the
3/8" groove and then with a ¼" dia. pin in the
5/16" groove. Continue shaping the tang radius until it slips
easily in the 5/16" dia hole in the handle. For a smaller
gouge radius use smaller grooves and smaller pins until you have
the desired radius. For larger radius gouges open up the blade
for about an inch by shaping over a larger dia. piece of steel
or a pipe using a plastic or lead hammer. Never hammer on the
blade itself with a steel hammer, as it will leave hammer marks
in the soft metal that are a nuisance to polish out later. At
this point, check the blade for a twist or straightness. Since
the metal is still soft it can easily be straightened with a pair
of pliers.
I am sure by this time you will be an expert at forming a gouge
blade from perfectly flat to as small as a 1/16" radius.
The blade itself need only be about an inch long and the rest
can taper into the tang. For smaller gouges you may have to use
narrower stock or else file the sides away if they become too
high. Other shapes will come to mind for carving difficult areas
of the scroll. While the blade is still in the annealed state—before
hardening—shape the cutting edge exactly as you want it on
the finished gouge, by filing or grinding, and then honing away
the feather edge until it looks like a finished gouge. I recommend
this because the metal is so thin it is almost impossible to grind
it after hardening without overheating and destroying the hardness
of the cutting edge. Any shaping after hardening must be done
on a slow wet wheel or by honing on a coarse oil stone.
Now comes the important critical part—the rehardening of
the cutting edge. This can be done by holding the tang with a
needle nose pliers and heating with a propane torch. It is not
necessary to harden the whole blade—in fact it is better
to leave the tang annealed and just harden the last half inch
of the blade. Direct the flame about one half inch from the cutting
edge and watch the color change. It will change from a yellow
to a brown, then blue, and finally a dull red. At a cherry red
color it will seem to stabilize and not change any further. This
is normal. See the chart, Fig 3. Remember the ice cube analogy.
You are changing the soft pearlite carbon to the hard martensite
carbon. Continue heating until you detect a change in color to
an orange red color, at which point quickly quench in a container
of water. A word of caution—keep the flame away from the
cutting edge and let the color creep to the edge rather than applying
the flame to the edge directly; otherwise the thin edge may be
burned and made useless. The biggest mistake one can make in hardening
high carbon steel is to be impatient and quench the steel before
it has all changed to martensite carbon, so watch for the orange-red
color. In this state the cutting edge is glass hard and very brittle
and could easily chip if used, so another operation is required
called tempering.
Tempering softens the hardness of the metal for the use intended.
Where the material is bent, as in a flat spring, or hammered on,
as in a cold chisel, the tempering temperature may vary from 400°
F to 550° F. Since the palm chisels are intended strictly
for shaving wood—no prying—I prefer to keep the cutting
edge fairly hard and temper to a temperature of about 400°
F. Here again we are making use of the color of the base metal
and, since the hardening of the blade left a black oxidized surface,
it is necessary to first polish the blade to the base metal. You
will want to do this anyway for appearances if you take pride
in your work. I clamp the tang in the vise and sand with strips
of aluminum oxide or emery cloth—not paper. If you have a
buffing wheel you can bring them to a nice polish as you would
your golf clubs. Tempering can be done in good light with a propane
torch, but it is risky because the temperature changes so quickly.
Use a smaller flame and hold it some distance away from the blade.
Here again point the flame toward the center of the blade—not
the cutting edge. Watch for the first sign of a pale yellow color
and let it slowly creep to the cutting edge. Immediately remove
the flame and allow to cool in air. A far safer and easier method
is to use the kitchen oven, preheated to 400° F. Try a test
piece to make sure you get a faint yellow color and remove and
allow to cool in air. With the oven method you can temper all
your blades at one time.
You may have your own idea for a handle, but I found the handle
shown in Fig. 1 comfortable to use and very easy to make. The
simplest way is to use ordinary 1" dia. hardwood dowels cut
in 2½" lengths. They are readily available in maple,
black walnut or other woods, or, if you have a wood lathe, you
can turn your own. I turned my handles out of cocobolo which I
had available. Drill a 5/16" dia. hole in the center of one
end, one inch deep, for the tang of the blade. If a 5/16"
pin is fitted tightly in the hole, the handle can easily be shaped
in the drill press using an improvised wood steady rest and an
old file ground for a scraping edge on the end. If you have a
wood turning lathe, I do not have to tell you how to turn a nice
handle. The gouge is assembled by coating the tang and the hole
with epoxy cement, inserting the tang and then inserting a one-inch
length of ¼" dia wooden dowel to fill up the hole.
Add additional epoxy cement until it is flush with the top.
The final sharpening is done by honing only, and finally stropping
on a leather-faced wheel. See the reprint of my article in the
May, 1966, Bulletin. Never attempt to grind the edge on your electric
grinder. The metal is so thin that you will soon burn the edge
and render the gouge useless. A slow rotating wet wheel is permissible,
but usually a coarse hone will remove any nicks or reshape the
wheel.
With a nice set of gouges it is wise to make some sort of block
for mounting them on the bench, or, better yet, a nice hinged
box such as that at the beginning of the article, rather than
let them rattle around in a drawer.
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