Round-nose chisel. Round-nose chisels
make circular grooves and chip inside corners with a
Diamond-point chisel. The diamond-point
chisel is used to cut V-grooves and sharp corners.
Repair. Nicked or battered chisels may be
repaired by grinding. If necessary, temper can also be
Grinding. Chisels are usually ground to a
70-degree angle, but that may be as high as 90-degrees
for harder substances. Proceed as follows:
Set the rest on the grinding wheel to
adjust for the desired bevel.
Eye protection will be worn when
grinding chisels. Failure to comply may
result in serious injury to personnel.
Move the chisel from side to side
while grinding so that the cutting edge will be slightly
Ensure that the bevels are kept
centered or the cutting edge will not be centered.
frequently in water.
Retempering. If temper has been lost
during grinding, retemper as follows:
Heat the entire chisel to cherry red
in a gas furnace or a charcoal fire.
Grasp the chisel in the center with
tongs and dip the cutting end in clean, cold water to a
depth of 1 1/4 inch.
Turn the chisel and dip the head in
the water to a depth of about 1 inch.
Quickly polish the hardened ends
with a file or abrasive cloth, Federal Specification P-C-
451, and observe the color returning from the heated
center of the chisel to the ends.
Dip the cutting end each time it
becomes purple, and the head each time it becomes
When the red disappears, dip the
Care. Observe the following practices for the
care and upkeep of chisels:
Protect the cutting edges by installing
Store in racks or where they may not be
chipped or broken.
Lubricate with a light coat of oil before
Regrind broken or chipped edges before
4-10. Punches. Punches usually are made of carbon
steel tempered on both ends. They generally are
classified as solid punches and hollow punches and are
designed according to their intended use. Hollow
punches vary in size. Solid punches vary both in size
and in point design.
Solid Punches. Solid punches are named
according to their shape and are designed for various
paragraphs describe the common types of punches used
in aircraft maintenance.
Prick punch. A prick punch, shown
in figure 4-58, is used to place reference marks in metal.
It is also often used to transfer dimensions from a paper
pattern directly onto the metal. It is relatively slender
and is tapered to a point of about 30 degrees. The
following precautions should be taken when using a
Never strike a prick punch a heavy blow with the
hammer because it could bend the punch or
cause excessive damage to the item being
Do not use a prick punch to remove objects
from holes because the point of the punch will
spread the object and cause it to bind even