TM 1-1500-204-23-11
(4) Sawing. Sawing with a band saw, saber
dried after machining to remove moisture. See para-
saw, radial arm saw, circular saw or table saw can
cut panels of either solid laminate or honeycomb
3-5l about coolant. Machining boron iber composites
successfully. Water as a coolant has been found to
will damage ibers resulting in strength loss.
be useful to remove surf and cool the cutter and the
panel.
(1) Damage removal. Use 80 grit diamond
abrasive router bits and the template method described
(a) A bandsaw blade with ine teeth that is
in paragraph 6-4b1. Use a feed rate of 2 inches per
run backwards or has a raker set with
minute.
the teeth alternately reversed produces
the best quality (see igure 3-1). Some
(2) Repair Joint Machining. There are two
fuzzing that remains on the edges after
methods of performing repairs to boron-epoxy bonded
a cut may be removed by light wet sand-
patches, ield repairs and depot repairs.
ing, with the sanding directed in towards
the laminate from the edge.
(a) Field Repairs. Field repairs to boron/ep-
oxy composites use externally bonded patches. The
(b) A table saw, radial arm saw, circular
blunt cut repair joint is formed during the damage
saw or cutoff saw with ine teeth run
removal operation.
backwards or alternately reversed teeth
produce good quality cuts. Carbide
(b) Depot Repairs. Depot repairs to boron-
tips are usually required. Some fuzzing
/epoxy composites use step joints. The step joint
remains on the edges after a cut may
uses a controlled depth router and 1.0 inch diameter
be removed by light wet sanding, with
diamond plated router bits.
the sanding directed in towards the
laminate from the edge.
b. Drilling Boron-Epoxy Composites. Hand drill-
ing small diameter holes for performing resin injection
(c) A traditional hole saw may provide sat-
repairs is the only drilling allowed on boron/epoxy
isfactory results on aramid reinforced
surfaces. Carbide is the speciied drill bit material.
composite materials only when used in
Use a 2,000 RPM drill motor, a carbide twist drill and
the reverse cutting direction. Hole saws
a maximum feed rate of 0.5 inch per minute.
do not work well on aramid laminates.
Routers or ly cutters made from high
c. Routing. Boron requires diamond-coated router
speed steel or carbide work well when
bits and a supply of approved coolant, either water
cutting aramid composite materials.
or alcohol based.
(5) Sanding & Grinding. Grinding wheels of
d. Reaming. Reaming boron requires diamond-
alumina composition run fast at about 6500 surface
coated reamers.
feet per minute with a shallow depth cut of 0.0005 to
0.001 inch and water will produce a desirable inish
6-12. FIBERGLASS-THERMOSETTING RESIN RE-
which has a glazed appearance. Sanding with silicon
PAIRS. Refer to system speciic manual for iber-
oxide abrasive paper of 80 to 100 grit with water as
glass/thermosetting resin repairs.
a lubricant and the sanding action directed towards
the interior of the material ensures cleaned, trimmed
6-13. HONEYCOMB CORE REPAIR PROCESS. M-
edges.
achining honeycomb core replacement sections can
be dificult due to the fragile nature of honeycomb
6-11. BORON-EPOXY REPAIRS. Boron is much
core. Core densities of 3.5 pounds per cubic foot
more dificult to drill or machine than other compos-
(PCF) or less provide little support for machining. The
ites. Diamond-cutting tools are used when drilling
thin foil used in the construction of aluminum core
boron laminates or hybrid laminates containing boron.
easily "rolls over" when machining 90 degrees to the
The same tools used to drill carbon generally work
cell axis. In addition, the core has little strength 90
well for boron.
degrees to the cell axis and is easily distorted if it is
not stabilized during machining. The core is strongest
a. Machining Boron-Epoxy Composites. Dia-
along its cell axis. Sawing expanded honeycomb,
mond plated tools are the only tools acceptable for
either aluminum or aramid, is usually done with a
machining boron iber composites. Water must be
special high speed bandsaw with a blade speed of
used to cool the boron during machining and drilling
16,000 feet per minute.
operations to avoid heat damage. The part must be
6-24