Page:Popular Science Monthly Volume 88.djvu/159

Popular Science Monthly must be turned first in one direction and then in the other.

A valve grinding tool patterned largely after a breast drill is shown at Fig. 11, D. This is worked in such a manner that a continuous rotation of the operating crank will result in an oscillating movement of the chuck carrying the screw driver blade. The bevel pinions which are used to turn the chuck are normally free unless clutched to the chuck stem by the sliding sleeve which

ing the surface of a valve head when the usual form of valve head truer is not available is indicated at Fig. ii, £. The valve heads are usually provided with a small depression in the center known as a countersink which is designed to act as a support foe the valve when it is being machined from the forging. The stem of the valve is caught in the chuck of a bit stock and rested on any sharp point on a wall or bench. This can be easily made by driving a large wire nail

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��must turn with the chuck stem and which carries clutching members at each end to engage similar members on the bevel pinions and lock these to the chuck stem, one at a time. The bevel gear car- ries a cam piece which moves the clutch sleeve back and forth as it revolves. This means that the pinion giving forward mo- tion of the chuck is clutched to the chuck spindle for a portion of a revolu- tion of the gear and clutch sleeve is moved back by the cam and clutched to the pinion giving a reverse motion of the chuck during the remainder of the main drive gear revolution.

A method that can be used for smooth-

��in the bench from underneath so that the point projects through the bench. The bit stock is briskly turned by a help- er and the rough spots are removed from the seat with a fine file, care being taken not to change the taper of the valve head. The valve stem could be turned much faster and a superior finish obtained if a breast drill were used instead of a bit stock, though with care a very credit- able job may be done with the latter.

One of the things to watch for in valve grinding is clearly indicated at Fig. ii. F. It sometimes happens that the ad- justing screw on the valve lift plimger or the valve lift plunger itself does not

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