Figure 5-16.--Toolholders for carbide inserts.
insert. To determine style, you need to know
rigidity of the tool and work and where you can
maintain high machining speeds. Negative rake tools
something about the particular machine tool you are
using and the operations you will do on it. Figures
5-16 and 5-17 show some of the styles available for
negative rake tools are stronger and produce
toolholders and boring bars.
TOOLHOLDER AND CARBIDE INSERT
You may use negative rake inserts on both sides,
IDENTIFICATION. --The carbide and toolholder
doubling the number of cutting edges per insert. This
manufacturers and the American Standards
is possible because end and side relief are provided by
Association (ASA) have adopted a system to identify
the angle of the toolholder rather than by the shape of
toolholders and inserted carbides. The system is used
to call out the toolholder geometry and to identify
Use positive rake inserts where rigidity of the tool
inserts. You'll find these charts in manufacturer's
and work is reduced and where high cutting speeds
catalogs; copy them and keep them in your toolbox.
are not possible; for example, on a flexible shaft of
small diameter. Positive rake tools cut with less force
We have given you an overview on carbides;
so deflection of the work and toolholder should be
certainly not everything you need to know. You also
reduced. High cutting speeds (sfpm) are often not
must work with personnel who know how to use them
possible on small diameters because of limitations in
and then learn by using them yourself. Also, a
number of carbide manufacturers offer schools to help
you understand carbides and their uses.
INSERT SIZES.--Select the smallest insert that
can sustain the required depth of cut and feed rate.
The depth of cut should always be as great as
possible. The rule of thumb is to select an insert with
Other than diamond tools, ceramic cutting tools
cutting edges 1 1/2 times the length of cutting edge
are the hardest and most heat resistant available to the
engagement. The feed for roughing mild steel should
machinist. A ceramic cutting tool can machine metals
be approximately 1/10 the depth of cut.
that are too hard for carbide tools, and they can
TOOLHOLDER AND BORING BAR
sustain cutting temperatures up to 2,000°F.
STYLES. --Tool style pertains to the configuration of
Therefore, you can use ceramic tools at cutting speeds
toolholders and boring bars used to hold a carbide
two to four times greater than cemented carbide tools.