Page:Practical Treatise on Milling and Milling Machines.djvu/53

Rh

Spiral Head—Indexing and Cutting Spirals

The mechanism known as the spiral head constituted one of the fundamental parts of the original universal milling machine. Its primary purpose was that of indexing and rotating work in

conjunction with the movement of the table for cutting flutes in twist drills. The great possibilities it offered in cutting a large range of spirals, and for doing many other jobs, were soon recognized and developed, until it is now used for an endless variety of operations. With it, ordinary indexing to obtain even spacing on the periphery of pieces, as in cutting teeth in cutters, ratchets, clutch gears, gear wheels and flutes in reamers, taps, drills, etc., can be quickly accomplished. Spiral forms of all common leads can be accurately reproduced by its use.

The spiral head and foot-stock are furnished as a part of all universal milling machines and can be applied, with few exceptions, to plain and vertical spindle machines. Used in connection with a vertical spindle milling attachment, on a plain machine, much the same variety of work can be done as on the universal milling machine.

In construction, spiral heads of today embody the same principles as the one on the original universal milling machine, but improvements have made them more solid and convenient to operate. Likewise, improvements have been made in the design and construction of the foot-stock.

Since our spiral head is typical of these mechanisms, a description of its various points may aid in understanding the methods of indexing and cutting spirals. The head itself consists of a hollow, semi-circular