In discussing cutting tools for
the planer and lathe, planer tools will first come under our
notice as being the simplest and requiring the least skill
Every mechanic has doubtless
observed that if the chip be unwound from the spiral shape
it assumes in leaving the tool, and projected in a straight
line, it is shorter than the surface from which it came.
This is due mainly to the compression of the metal in the
direction of the cut, and the possibilities of saving power
and strain upon the machine by giving proper cutting angles
to the tools and reducing this compression to a minimum is
Proper Rake on Lathe and Planer
Tools of the work, and having no side rake either, it simply
does not cut, but shoves or crowds the metal forward,
producing a chip made up of little splints. It cannot exert
any force tending to lift or curl the chip.
The tool is wholly wrong; nor
would it materially improve it to grind it like the tool
shown in the little sketch at the right, which goes to the
other extreme, and would spring into the work. A tool must
first of all be heavy enough at the back or heel to resist
the horizontal cutting force, and consequently should have
very little clearance.
The 7 degrees clearance shown
in the lathe tool in the upper view, Fig. 2, is too much for
a planer tool, while the 3 degrees of the lower sketch is as
small as can be used safely. Theoretically if the point
leads by only a thousandth or two it will perform its
There should be very little top
rake on account of its tendency to make the tool dig into
the cut; but this can be compensated for by giving
considerable side rake..