Cutting Tools Worked by Hand and Machine by Robert Henry Smith

Author:Robert Henry Smith
Language: eng
Format: epub
Publisher: Cassell, Petter, Galpin& co.
Published: 1882-03-25T05:00:00+00:00

Pig. 33.

of obliquity in both pinion and wheel, the teeth of the latter cannot be made to lit well both the worm t and the pinion z.

The design shown in Fig. 33 is a great improvement and simplification of the necessary mechanism. The diagram shows the saddle in plan, with the top slides removed, and with the lathe bed and the rack y broken oflF. The latter is secured to the front side of the bed, and the pinion x (seen dotted) exerts its driving pressure on the rack much more nearly in a direct line underneath

the cutting point of tlie tool, where the resistance to motion is generated, than in the fonner design.

The worm-wheel u^ which gears into the worm «, not shown in the figure, is keyed fast on the shaft which runs to the front of the saddle. Near the front end of this shaft there is formed a cone, which fits into an internal cone cut in the boss of the pinion v, and another similar cone stands on the opposite side of this pinion, fitting into a similar recess in the front end of the boss. The pinion and the latter cone both run loose on the shaft, except when, by means of the large nut seen at the end of the shaft, the external and internal cones are tightened and locked together by friction. The friction-cone coupling takes the place of the sliding of the spur-wheels on their feathers, and the tightening or loosening of the cones is effected by a very small rotation of the clamping nut. The putting the self-acting rack feed into and out of gear is by tJiis means made very much more handy and expeditious. The importance of this advantage is not limited to the saving of a little trouble on the part of the turner. If the workman has to turn a parallel length on his work which joins on to a flat surface perpendicular to the axis of rotation, he must exercise the greatest care in turning the last portion of the parallel run close to the corner, because if he goes the least distance too far he may spoil the flat face, and break his tool as well. With the mode of engagement shown in Fig. 32 there is always a risk of the teeth sticking so hard together when they are in gear that the first effort of the workman will not be sufficient to disengage them. The turner cannot afford to run this risk at the last instant of the parallel cut, and he must, therefore, throw fche self-acting feed out of gear when his tool is still at some considerable distance from the comer, and must finish the cut up to the comer by hand feed with the top slide. This process is altogether clumsy and wasteful of time; and although the hand feed at the last small fraction of an inch from the comer cannot be dispensed

[Chap VL

Mrith even with the friction-cone

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