Page:Practical Treatise on Milling and Milling Machines.djvu/57

Rh disengaging the worm from the wheel. To re-engage the worm, reverse the above operation.

Effect of Change in Angle of Elevation on Spindle. If the angle of the spiral head spindle is changed during operation, the spindle must be rotated slightly to bring the work back to the proper position, for when the spindle is elevated or depressed, the worm wheel is rotated about the worm, and the effect is the same as if the worm were turned.

Foot-stock. The foot-stock shown in Fig. 7 is for supporting pieces of work that are milled on centres or the outer ends of arbors, and pieces that are clamped in a chuck. The centre is adjustable longitudinally, and can be elevated or depressed by means of a rack V, and pinion actuated by hex U. It can also be set at an angle out of parallel with the base when it is desired to mill drills, taper reamers, etc., so that it can be kept in perfect alignment with the spiral head

Fig. 7

centre. The advantage of this is readily appreciated from the fact that by the use of centres that cannot be adjusted, work is aprt to become cramped at certain pisitions during its revolution, and, as a result, even spacing cannot be obtained.

When set in any position, the centre is firmly held by means of the nuts W, X and Y. Set screw S prevents endwise movement of the elevating pinion.

Two taper pins, one of which is shown at Z, are used to quickly and accurately locate the foot-stock centre in line with the spiral head centre, when the centres are parallel to the top of the table. They may be loosened by twisting a little with a wrench.

Fig. 8 shows a gauge that is very handy to use for quickly adjusting the foot-stock centre in line with the spiral head centre