Craftsman 315.175341 - Manual (Page 17)

OPERATION
RATE OF FEED
The proper rate of feed depends on several factors: the
hardness and moisture content of the wood, the depth
of cut, and the cutting diameter of the bit. When cutting
shallow grooves in soft woods such as pine, you may
use a faster rate of feed. When making deep cuts in
hardwoods such as oak, you should use a slower rate of
feed.
The best rate of feed is one that does not slow down the
router motor more than one-third of its no load speed. If
you feed the router too fast, it will take large chips out of
the wood and leave gouge marks. If you feed the router
too slowly, it will scorch or burn the wood.
F e e d in g T o o F a s t
S e e F ig u re 2 0 .
Clean, smooth routing and edge shaping can be done
only when the bit is revolving at a relatively high speed
and is taking very small bites to produce tiny, cleanly
severed chips. If you force the router to move fonward
too fast, the RPM of the bit becomes slower than normal
in relation to its forward movement. As a result, the bit
must take bigger bites as it revolves. Bigger bites mean
bigger chips and a rougher finish. Also, because bigger
bites require more power, the router motor may become
overloaded.
Under extreme force-feeding conditions, the relative
RPM of the bit can become so slow—and the bites it
has to take so large—^that chips will be partially knocked
off (rather than fully cut off). This causes splintering and
gouging of the workpiece.
The router is an extremely high-speed tool, and will
make clean, smooth cuts if allowed to run freely without
the overload of a forced feed. You can always delect
force feeding by the sound of the motor. Its high-pitched
whine will sound lower and stronger as it loses speed.
Also, the strain of holding the tool will be noticeably
increased.
F e e d in g T o o S lo w
S e e F ig u re 2 1 .
It is also possible to spoil a cut by moving the router
forward too siowly. When you advance the router into
the work too slowly, the revolving bit does not dig into
new wood fast enough to take a bite; instead, it merely
scrapes away sawdust-like particles. Scraping produces
heat, which can glaze, burn, or mar the cut and in
extreme cases, can even overheat the bit,destroying
its hardness.
In addition, when the bit is scraping instead of cutting, it
is more difficult to control the router. With practically no
load on the motor, the bit revolves at close to top RPM,
and has a much greater than normal tendency to
bounce off the sides of the cut (especially if the wood
has a pronounced grain with hard and soft areas). As a
result, the cut produced may have rippled, instead of
straight, sides.
Feeding too slow can also cause the router to take off
in a wrong direction from the intended line of cut.
Always grasp and hold the router firmly with both hands
when routing.
You can detect when you are feeding the router too
slowly by the runaway, high-pitched sound of the motor
or by feeling the wiggle of the bit in the cut.
Fig. 21
TOO FAST
Fig. 20
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