Machining Fundamentals
196
Tooth pattern determines the efficiency of a
blade in various materials. The standard tooth
blade pattern is best suited for cutting most ferrous
metals. A skip tooth blade pattern is preferred
for cutting aluminum, magnesium, copper, and soft
brasses. The hook tooth blade pattern also is recom-
mended for most nonferrous metallic materials.
See Figure 12-13.
For best results, consult the blade manufac-
turer’s chart or manual for the proper blade charac-
teristics (set, pattern, and number of teeth per inch)
for the particular material being cut.
This typically includes checking wheel alignment,
guide alignment, feed pressure, and hydraulic
systems.
12.4 USING RECIPROCATING AND
BAND SAWS
Most sawing problems can be prevented by
careful planning and observing a few rules. These
apply to both reciprocating and band saws.
12.4.1 Blades Breaking
Blades are normally broken when they are
dropped on the work. A loose blade or excessive
feed can cause the blade to fracture. Loose work can
also cause blade damage, as will making a cut on a
corner or sharp edge where the three-tooth rule is
not observed. Broken blades can normally be
avoided with proper machine setup.
12.4.2 Crooked Cutting
This problem is usually the result of a worn
blade. Remember to reverse the work after replac-
ing a blade, and start a new cut on the opposite side.
See Figure 12-15. A loose blade or a blade rubbing
on a clamping fixture will cause the same problem.
It can also be caused by excessive blade pressure on
the work or by worn saw guides.
12.4.3 Blade Pin Holes Breaking Out
This reciprocating blade problem can be caused
by dirty mounting plates or too much tension on the
blade. Worn mounting plates can cause a blade to
twist and strain in such a way that the pin hole will
break out.
Standard tooth
Skip tooth
Hook tooth
Figure 12-13. Standard tooth blades, with rounded gullets, are
usually best for most ferrous metals, hard bronzes, and hard
brasses. Skip tooth blades provide for more chip clearance with-
out weakening the blade body. They are recommended for cut-
ting aluminum, magnesium, copper, and soft brasses. Hook
tooth blades offer two advantages over skip tooth blades—
easier feeding and less “gumming up.”
12.3.2 Installing a Band Saw Blade
If the saw is to work at top efficiency, the blade
must be installed carefully. Wear heavy leather
gloves to protect your hands when installing a band
saw blade.
Blade guides should be adjusted to provide ade-
quate support, Figure 12-14. Proper blade support is
required to cut true and square with the holding
device.
Follow the manufacturer’s instructions for
adjusting blade tension. Improper blade tension
ruins blades and can cause premature failure of
bearings in the drive and idler wheels.
Cutting problems encountered with the band
saw are similar to those of the reciprocating hack
saw. Most problems are caused by poor machine
condition. They can be kept to a minimum if a
maintenance program is followed on a regular basis.
Blade guides
Figure 12-14. Adjust blade guides to provide adequate blade
support; otherwise, blade will not cut true. (W.F. Wells)