Craftsman 351.217520 Manual Del Operador página 9

USING WOODWORKING CHISELS
SELECTION OF CHISELS
Better chisels have handles approximately 10" long to provide
plenty of grip and leverage. Sharp tools are essential for clean,
easy work. Select tools that will take and hold keen edges.
Gouge Skew Parting Tool
Spear Point Flat Nose
Round Nose
Figure 21 -The Six Commonly Used Chisel Types
THEORY OF TURNING
The two classes of chisels are those intended primarily for
cutting, and chisels used only for scraping.
• The cutting chisels are the gouge, skew and parting tool.
These are the most used. They are commonly sharpened
to a razor edge by honing on both sides.
• The scraping chisels are the flat nose, round nose and
spear point. These are not honed on the flat sides - the
wire edges produced by grinding are left on to aid in
the scraping process.
Cutting Chisel Scraping Chisel
Figure 22
Cutting and Scraping
• To cut, the chisel is held so that the sharp edge actually
digs into the revolving work to peel off shavings.
• To scrape, the chisel is held at a right angle to the work sur-
face. This tool removes fine particles instead of shavings.
Figure 23
Cutting Scraping
Many operations require that the cutting chisels be used for
scraping, but scraping chisels are practically never used for
cutting. Scraping dulls a chisel much faster, especially the
razor sharp cutting chisels.
Cutting is faster than scraping and produces a smoother finish
which requires less sanding. However, it is far more difficult to
master. Scraping, on the other hand, is far more precise and
easier to control.
When You Can Cut and When You Must Scrape
There are two different approaches:
• One approach is toward a circumference of the workpiece
(for example turning down the outer surface of a cylinder or the
inner wall of a hollow round box). In this approach, the surface
being turned travels under the chisel edge like an endless belt.
• The second approach is toward the diameter of a workpiece
(as when turning the face of a faceplate turning, or the side
of a large shoulder on a spindle turning). In this approach, the
surface being turned rotates like a disc under the chisel edge.
• Sometimes the optimum approach will be a combination
of both methods.
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Diameter
Approach
Figure 24
Either a cutting or scraping action can be used when the
approach is toward a circumference - the shaving is removed
like a peeling from a potato. Scraping can only be used when
the approach is toward a diameter. The reason is obvious
when you consider that faceplate turning practically always
requires removal of wood across the grain. Wood does not
peel easily across the grain and attempts to use any inappro-
priate cutting methods will likely result in damage to the work-
piece. There is also danger that the tool could be pulled from
the hands of the operator.
In general, a cutting action is used for the majority of
spindle turning operations while faceplate turning is usually
accomplished by the scraping method. When a combination
approach is to be used, the operator will have to judge, by
the feel of the work, when to stop cutting and start scraping.
Never try to cut when it becomes difficult to hold the chisel
against the roughness of the wood grain.
How to Position Tool Rest for Circumference Cutting
When cutting, the object is to pierce the outer skin of wood
to a certain desired depth and then to hold the chisel steady
with the bevel edge parallel to the work circumference so
that it will peel off a shaving at this desired depth.
• The only sure method of holding the chisel steady is to
rest the bevel against the work (Figure 25A, page 10).
When the tool rest is at the proper height, the chisel can
be held with the bevel pressed against the work, and the
tool rest will act as a fulcrum to support the chisel against
the downward force of the revolving work.
• If the rest is placed too low, so that the chisel is held with
the bevel out from the work (Figure 25B, page 10), the
cutting edge will continue to dig deeper into the work. It
will dig in until the "bite" becomes so deep that your hands
have difficulty holding the chisel - then the improperly
supported chisel will begin to bounce or chatter against
the workpiece.
• If the rest is placed too low, the chisel must be held
extremely high to position the bevel against the work
(Figure 25C, page 10). Then the rest loses most of its
value as a fulcrum and the downward force of the revolving
workpiece tends to kick the chisel back out of your hands.
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