To utilize RSC to its fullest potential proper saw selection
is vital. Decisions on several items must be made: saw material, saw diameter,
saw thickness, number of teeth, tooth angle, and type of surface treatment.
Saws are available in two materials, carbide and high speed steel. SFM of the
job will usually determine which is to be used--carbide surface feet rates
require solid carbide saws. Carbide saws also cut more cleanly which results in
better surface finishes, and less burr or reduced nib. Cuts with carbide saws
are less demanding on the equipment and tool life is 5 to 10 times better than
with high speed steel saws. Heat sensitive materials also require the use of
carbide saws. When running at high speed steel SFM rates, high speed steel saws
can be used. On ferrous materials, however, cutting with saw blades requires
the use of an oil coolant with active sulfur to prevent galling.
The needed thickness of the saw is generally 1/3 that of
single point tooling and thus, the reason for the substantial material savings.
Aggressive cutting, deep cuts, and larger diameter materials might require a
thickness greater than that rule of thumb, while with softer materials, smaller
diameters, and thin-walled materials a narrower saw is possible. With RSC, the
kerf lost between pieces (average of .045") is 50%-75% less than that lost
by the conventional cutoff. More pieces are obtained from one bar of stock. The
higher yield per bar reduces stock purchases, stock handling, and machine
stock-ups. Also, because kerf is reduced, there is less waste to contend with,
and more importantly, the scrap is easier, safer, and less costly to handle;
each saw tooth only cuts a small portion of the stock so the scrap produced by
using RSC consists of tiny flakes rather than long, sharp, coils.
The diameter of the saw is determined by the distance to the cut, the depth of
the cut, the configuration of the tooling zone, and other attachments. Saws for
RSC range from 2-1/2" to 6" in diameter; the average is 4".
The number of teeth on a saw requires careful consideration. A coarse tooth
configuration (for example, 90 teeth on a 4" dia. saw) is better for
cutting 3/4" dia. or larger workpieces. A coarser configuration is also
appropriate for workpieces with a hole. Finer configurations, such as 130 or
more teeth on the same 4" saw, are best for small diameters, cutting to
center, and thin-walled tubing.
The last consideration for the geometry of the saw is the cutoff angle on the
tooth. Cutoff angles reduce burr and nibs and produce a better surface finish.
However, the smallest angle possible should be used to gain the desired results
because larger cutoff angles could affect tool life. A good starting point for
a carbide saw is a 7° cutoff angle and for a high speed steel saw a
10° angle.
Finally, many surface treatments are available: Kalite
Sodite, Liquid Nitride, Titanium Nitride, Titanium CarboNitride, etc. Surface
treatments increase tool life and produce better surface finishes. High carbon
steel and 52100 bearing steels require TiN or TiCN coatings.
In general, saw life is 5 to 10 times better per grind than
single point tool life. Because of the light chip load, the interrupted nature
of the saw cut (each saw tooth cuts for only a brief moment at a time), and the
side clearance on saws, a rotary saw cut builds up very little heat. The heat
stays in the chip which is immediately carried away from workpiece and saw by a
strong coolant flow. Therefore, tool life is greatly improved because cutting
off is far less demanding on a saw than it is on a single point tool.
Saw
Availability
Watkins makes all saws to order because of the endless
combinations of different OD's, number of teeth, thicknesses, angles, and
surface treatments. Please allow a 2-3 week lead time when ordering saws (an
additional week for saws with a surface treatment). Saw blades are
available in high speed steel (M2 & M42) and solid carbide for cutting off,
slotting, and forming. Watkins specializes in saws 2.5" to 6.0" in
diameter and thicknesses from 0.032" to 0.093". Number of teeth can
vary from 60 to 230 depending on your application. Finally, many surface
treatments are also available: Kalite Sodite (KS), Liquid Nitride, Titanium
Nitride (TiN), and Titanium Carbonitride (TiCn). When selecting a saw,
please do not hesitate to contact Watkins for technical help.
Saw Features