Page:Practical Treatise on Milling and Milling Machines.djvu/55

Rh the table advances, so that the cutter produces a spiral cut in the work. For rapid indexing, when cutting flutes in taps, reamers, etc., the worm A, is disengaged and the spindle turned by hand, the divisions being made by means of the index plate c, which is fastened to the

nose of the spindle, and may be locked by the pin D.

The spindle may be revolved continuously as when cutting spirals, or may be securely locked after being revolved a desired amount, as in indexing for cutters, the teeth of gears, clutches, ratchets, etc.

It is possible to swing the head in its bearings so that the front end of the spindle can be set to any desired angle from 10&deg below the horizontal up to 5&deg beyond the perpendicular without throwing the driving members out of mesh. Graduations on the front exge of the head indicate the angle of elevation to half degrees.

The design of the head is such that it permits unusually long and wide bearings. Furthermore, it isets very low and can be so firmly clamped to the base that the whole mechanism practically becomes on solid casting. Hence, it provides a particularly rigid support for the work, which is a factor of much importance in the calss of work that is done upon this mechanism.

Index Plates and Change Gears. Three index plates are furnished with the spiral head, and contain circles with the following numbers of holes:—




 * width="75pt" align="right" |Plate 1—
 * width="10pt" align="left" |15,
 * width="10pt" align="left" |16,
 * width="10pt" align="left" |17,
 * width="10pt" align="left" |18,
 * width="10pt" align="left" |19,
 * width="10pt" align="left" |20.
 * align="right" |Plate 2—
 * align="left" |21,
 * align="left" |23,
 * align="left" |27,
 * align="left" |29,
 * align="left" |31,
 * align="left" |33.
 * align="right" |Plate 3—
 * align="left" |37,
 * align="left" |39,
 * align="left" |41,
 * align="left" |43,
 * align="left" |47,
 * align="left" |49.
 * }
 * align="left" |49.
 * }

The change gears that are furnished have the following numbers of teeth: 24 (2 gears), 28, 32, 44, 48, 56, 64, 72, 86 and 100.

Graduated Index Sector. Without the graduated index sector, much care must be exercised in counting the holes in an index plate when indexing to obtain any given number of divisions. Such a sector enables the correct number of holes to bo obtained at each indexing with little chance for error. It is shown in Fig. 5 and