T.O. 1-1A-9
This material will exceed the performance of some of the other types of tools when used for fragile tools such as drills,
taps, etc., because it does not break as easily as the other types. Stock material is obtainable in accordance with
Federal Specification QQ-T-580 where required for local fabrication of high carbon tools etc.
b.
High speed tool steel is the most common type used for machining except on the higher silicon alloys.
(1)
Availability, reasonable cost.
(2)
Heat resistance (will retain cutting edge up to about 950F dull red).
(3)
Permits use of large rake angle required. Federal Specification QQ-T-590 applies to stock material. All
the various classes (T1, T2, T3, etc.) may be used for machining aluminum. Class T1 (18-4-1) general purpose type is
the most widely used.
c.
Where long production runs are involved cemented carbide (solid or tipped) tools give better service. The
carbide tools have been known to last thirty times longer than high speed tool steel. The carbide tools are also
recommended for cutting high silicon content alloys. Because of the brittleness of the cemented carbide tool the cutting
angle should be greater than those recommended for high carbon/high speed steels.
d.
Diamond tipped tools should only be used for light finishing cuts or special finishing operations. Normal cutting
of 750 900 are used with top rake angles of s6 100. Tool projection (or set) should be slightly above center line (CL) of
the work.
3-180. TURNING. To properly perform the turning operation firmly attach the work to the machine (lathe) chuck, collet
or faceplate. The work should be held in the best manner to minimize distortion from chuck or centrifugal force action
during the turning operation. Long rods/stock should be supported by ball or roller bearing tailstock centers which are
more satisfactory than solid or fixed centers in resisting thrusts from centrifugal force and thermal expansion. Soft liners
may be used between work and machine jaw faces to prevent jaw teeth from damaging/marring work piece. When it is
necessary that work be held by clamping from inside diameter outward the tightness of jaws should be checked
frequently to be sure that work is not being released as a result of thermal expansion.
3-181. The recommended cutting fluids are the soluble oil emulsion which combine the functions of cooling and
lubricating for general purpose use. For heavy cutting especially when speeds are low, lard oil such as Specification C-0-
376 or mineral oil, Specification W-0-241 is recommended. In practice it will be found that some machining operations
can be performed dry.
3-182. Tables 3-22 and 3-23 cite suggested turning speeds, tool angles and feeds. Tool projection in relation to work
should be set at or slightly above work piece center line. Sturdy construction of tools and holders is essential to minimize
vibration/chatter at the high speeds aluminum alloys are machined.
NOTE
Parting tools should have less top rake than turning tools. Recommend top rake angles of
120 20° and front clearances of 4°0 80 grind face concave (slightly) and so that corner
adjacent to work will lead opposite corner by 4°0 120 or as required for best results.
3-183. MILLING-ALUMINUM . Milling of aluminum alloys should be accomplished at high cutter speeds. The limitations
will usually depend on the machine and type cutters used. The reason for the higher cutter speeds is that at low speeds
the cutters will have a tendency to load and gum. This will normally clear as the speed is increased.
3-184. The tooling for milling should be selected according to the operation and duration/size of job to be performed.
The cutters 8ho,ld have fewer teeth and should be ground with more top and side rake than those used for milling steels.
Most operations can be accomplished with spiral cutters. Nick tooth cutters are used when reduction in size of chips is
required. Solid-tooth cutters with large helix angles are used where free-cutting tools are required.
When cutters with large helix angles are used it is often necessary that two interlocking cutters of opposite helixes be
employed to alleviate axial thrust.
3-185. Tool alloys should be selected for milling aluminum as follows:
a.
For short runs high carbon steel is normally satisfactory.
b.
For production runs of extended duration high speed steel is recommended.
c.
Where climb milling/high speeds are utilized, carbide tipped tools are recommended for extended runs.
3-42
