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similarly, if the workpiece is a soft metal such as
aluminum, each tooth will remove more material
and rapidly fill the blade gullet. For this reason,
use a blade with fewer tpi on soft metals.
an additional problem with an overly fine-pitched
blade is that the pressure each tooth exerts on the
workpiece is reduced. this limits the cutting ability
of the teeth and also results in a buildup of heat
and inefficient cuts.
the ideal blade pitch is one that doesn't overload
individual teeth (too coarse) and avoids excessive
chip buildup in the gullet (too fine) (figure 39).
Blade
(Correct TPI
For Workpiece)
Workpiece
figure 39. Correct TPI.
damage to the blade, rough cuts, poor cutting
performance, and overheating are all possible
signs of improper blade pitch.
if you feel your machine is not functioning properly
or performing to your standards, check that the
blade pitch is correct for the cut. the procedure
that follows is a basic starting point for choosing
blade pitch (tpi) for standard hss blades.
To select the correct blade pitch:
1.
measure the thickness of your workpiece.
—For solid workpieces, this measurement is
the length of cut taken from where the tooth
enters the workpiece, sweeps through, and
exits the workpiece. see (d) on the chart in
figure 40.
—For hollow or profiled workpieces, this
measurement is the wall thickness at its
thickest point (th).
-26-
2.
D or Th Inches (mm)
<1/16 (<2)
Gullet
Chips
blade feed rate refers to the period of time it takes
to cut through a workpiece. on the model g0682,
feed rate is controlled by the amount of pressure
exerted on the handle by the user. pulling hard on
the lever will result in a greater feed rate, whereas
only pulling lightly will result in a very slow feed
rate.
Cutting with a feed rate that is too slow can result
in lengthy, inefficient cuts and in some cases,
tooth dulling or overheating. the chips produced
by the cut will generally be thin or powdery.
Cutting with a feed rate that is too fast may cause
the blade to wander, resulting in cuts that are not
straight, and will generate excess heat and dull
the blade. the chips produced by the cut will gen-
erally be thick and hard. When cutting small or
thin-walled workpieces, the edges of the cut may
become rough or torn.
the best method for evaluating the feed rate is to
inspect the chips formed by the cut. refer to the
Chip inspection Chart on page 29.
0.5"
6–8
0.02"
refer to the "d or th" column of the blade
selection chart in figure 40, and read down
1"
4–6
1/16"
to find the workpiece thickness you need to
2"
3–4
3/32"
cut. read across to find the appropriate pitch
3"
2–3
(tpi) for the cut. For blade alternatives, see
4"
2
3/16"
Accessories on page 31.
5"
.8-1.5
Pitch (TPI)
1/16 (2)
1/8 (3)
1/4 (6)
1/2 (12)
1 (25)
2 (50)
3 (75)
>3 (>75)
figure 40. Blade selection chart.
blade feed Rate
g0682 12" Cold Cut saw (mfg. since 12/10)
8–10
5–7
4–5
1/8"
3.5–4
2
1/4"
.8-1.5
>7
Workpiece
7
6
Measurements
5
Th
4
Th
D
3
Th
2.5
<2.5
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