Drilling New Rivet Holes. Much care must be taken in duplicating
holes from reinforcing members, or the frame and skin can be ruined.
Such care is necessary because most ribs, stringers, and bulkheads
depend on the skin for some of their rigidity and they can be forced
out of alignment during drilling. The pressure from drilling forces
the skin away from the frame and causes the holes to be out of
alignment. This can be prevented by holding a block of wood firmly
against the skin while drilling. Also the drill must be held at a 90
angle to the skin during drilling or the holes will be out-of-round.
A smaller pilot drill must be used first when drilling through anchor
nuts. Care must be taken to avoid damaging the anchor nut threads.
The pilot holes are then enlarged to the proper size.
Marking New Holes. An angle attachment or flexible-shaft drill may
be necessary where a straight drill cannot be inserted.
If neither
of these drills can be used, mark the new section with a soft pencil
through the holes in the old section. Another method for marking new
hole locations is with a transfer or prick punch, shown in Figure 2-
7. Center the punch in the old hole and then hammer lightly on the
outside of the sheet with a mallet. The resulting mark can be used
to locate the hole in the new sheet.
Another way to locate the rivet holes without a template is to use
a hole finder similar to the one shown in Figure 2-8.
This device
makes a perfect alignment with the holes in the old section possible
while drilling holes in the new section of skin.
The hole finder
illustrated is made in two sections, an upper and a lower part,
bolted together at one end.
A guide rivet, at the free end of the
bottom section of the hole finder, drops into the old holes in the
sheet still in place. The free end of the hole finder's top section
has a hole that exactly matches the position of the guide rivet. The
new hole is drilled through this opening.
As the hole finder is
moved along, the guide rivet drops into an old hole and automatically
determines the new hole's location.
Figure 2-7.
Transfer Punch.
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