designed for locating and holding the work piece. These special vise jaws have locating stops that
make possible easy location of the work pieces. The special jaws convert a vise into a milling fixture.
DOWN MILLING
If down milling is used, all looseness must be eliminated in the table feed screw, as the motion of the
cutter tends to pull the work piece into the cutter. The machine must be designed with special features,
adapting it to down milling if this type of milling is to be used.
In down milling, the maximum chip thickness is obtained close to where the tooth contacts the work
piece. No built-up pressure is developed in down milling, and, therefore, no heavy burr (a protruding,
ragged metal edge) forms on the surface of the metal.
Down milling that is being done depends upon the side from that the work piece is fed to the rotating
milling cutter. In down milling, the portion of the tooth contact with the work piece shows a very good
finish. An element of the final milled surface is produced at the end of the tooth travel when the built-up
edge is completely developed. This could mean that the finish of the final surface might be of poorer
quality than produced by up milling.
UP MILLING
In up milling, the cutter rotates against the direction of feed as the work piece advances toward it from
the side where the teeth are moving upward. The separating forces produced between cutter and work
piece oppose the motion of work.
In up milling, since the cutter teeth come up from the bottom of the cut, the chip is very thin. It the
beginning where the tooth first contacts the work piece. Gradually, the chip increases in thickness,
reaching its maximum thickness where the tooth leaves the work piece.
In up milling, the material removed by each tooth starts with a minimum thickness and ends with a
maximum thickness.
The chip should form at the center, but due to the resistance of the material to penetration, the cutting
action is delayed somewhat and cutting starts slightly ahead of the center. The cutter slides over the
work piece to be machined until sufficient pressure has been built up to force it to bite into the surface of
the workspace to produce a chip.
The starting of the cutting in up milling is not recommended as the cutting edge of a tooth rubs along the
work piece surface at the start, and the beginning of the cutting is difficult. The opposite cutting
condition, or down milling, is better, since cutting edges remain sharp longer, and smoother surfaces
can usually be obtained.
RPM of the milling cutter=