Scale B also indicates the recommended width of
the scarf and the approximate number of plies of cloth
required for any given thickness. The number of plies
required is affected by the variation in the thickness of
the cloth, the viscosity of the resin used (the thicker the
resin, the fewer the plies), and workmanship. The
amount of cloth specified on scale C is based on the
maximum number of plies that might be used, and the
resin estimate is based upon an approximate resin con-
tent of 60 percent.
To illustrate the use of the nomogram, assume that
a repair is to be made to an 8-inch diameter hole in a
1/4-inch thick laminate. Looking at scale B, the recom-
mended width of the scarf is 4 inches, and the approxi-
mate number of plies of style #1000 glass cloth is 13 to
16. The average diameter will be 8 inches + 4 inches
(fig. 4-9) = 12 inches. Drawing a line between 12 inches
on scale A and 1/4 inch on scale B (see dotted line in
fig. 4-9), approximately 18 square feet of style #1000
glass cloth and 1 quart of resin are required. (As men-
tioned previously, the materials estimate may be 30 to
40 percent in excess of the actual requirement.)
PREPARING THE DAMAGED AREA.--The
next step is to prepare the damaged area. This is
accomplished in one of two ways. If the damage
extends only partially through the laminate, merely
grind the damaged area down to the sound laminate
with a disk or cone sander using a coarse abrasive. If
the break is all the way through the laminate, however,
the damaged area should be cut out on the first chalk
mark nearest the damage with a metal cutting handsaw
or reciprocating sabre saw (fig. 4-11). Then, scarf back
Figure 4-10.--Average diameter and area of a patch.
Figure 4-11.--Damaged area being cut away.
4-11