Planetary Thread Milling Machines
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Planetary Thread Milling Machines
Planetary Thread Milling Machines -
Conventional Machines.
Conventional thread milling machines are made in the universal and production types.
The Universal Machine is suitable for all forms of external or internal threads, except square threads, and is equipped with a full length lead screw. Change gears permit milling of threads with leads ranging from 1132 to 60 in. Pickoff gears in the cutter drive allow a wide speed range differential between the cutter and the work. The cutter head is mounted on the cross slide and swivels through an arc of 180. to accommodate any helix angle of thread, either right or left hand.
Either a single or multiple thread milling cutter is used for producing the thread. If the single cutter is used, the cutter must traverse the work or the work must traverse the cutter for the full length of the thread.
The cutter head is swiveled to the exact helix angle of the thread and the center of form on the cutter must be spaced if necessary, on the exact pivot center of the swivel head. When the thread permits the use of a multiple thread milling cutter, the spindle is set parallel to the work axis. If the thread is long or the pitch is coarse, an outer support should be attached to the spindle to prevent the cutter's springing away from the work.
The use of the multiple cutters is the fastest and most economical way to mill threads. With this type of cutter, the work rotates 1.10 revolutions.
A single form cutter is essentially like a milling cutter, heaving teeth in a single, annular row.
A multiple thread milling cutter has several annular rows of teeth that are perpendicular to the cutter axis, the rows not having any lead. The cutter is slightly longer than the tread to be cut.
Thread milling with multiple thread cutters is widely employed for making screw threads on ductile and hard steels, when the application of threading dies or die heads does not provide a sufficiently high class of surface finish, or leads to rapid dulling of the cutting tools.
Milling a Worn Thread With a Single Form Cutter
| A - Swivel head is pivoted to the thread helix angle α | B - Swivel center of cutter head & center of cutter form |
Conventional setup for milling external threads
A - Axis of cutter spindle and work are parallel
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