The solid type A, [Fig. 16], is used very extensively, but in shops where a great variety of work is being done and there are many odd-sized holes, some form of expanding arbor B can be used to advantage. This type, instead of being solid, consists of a tapering inner arbor M on which is placed a split bushing that can be expanded, within certain limits, by driving in the tapering member. The advantage of this type is that a comparatively small stock of arbors is required, as different-sized bushings can be used. This type can also be fitted to holes of odd sizes, whereas a solid arbor must be provided for each different size hole, unless the variation is very slight. The latter are, however, more accurate than the expanding type.
Another form of expanding arbor is shown at C. This type has a straight body N in which four tapering grooves are cut lengthwise, as shown, and there is a sleeve S, containing four slots that are located to correspond with the tapering grooves. Strips s are fitted into these slots, and as the part N is driven in, the strips are moved outward as they ascend the tapering grooves. By having different sets of these strips of various heights, one arbor of this type can be made to cover quite a range of sizes. It is not suited, however, to thin work, as the pressure, being concentrated in four places, would spring a flexible part out of shape.
Fig. 17. (A) Cone Arbor.
(B) Nut Arbor.
(C) Pipe Center
The cone arbor or mandrel shown at A, in [Fig. 17], is convenient for holding parts having comparatively large holes, as it can be adjusted for quite a range of diameters. The work is gripped between the two cones c and c1 which are forced together by nut n. The cones are prevented from turning upon the arbor by keys. This style of arbor should not be used for accurate work. The threaded arbor B is used for facing the sides of nuts square with the tapped hole. When a nut is first put upon the arbor, the rough side comes against an equalizing washer w. This washer rests against a spherical seat so that it can shift to provide a uniform bearing for the rough side of the nut, even though it is not square with the tapped hole. This feature prevents the nut from being canted on the arbor and insures an accurately faced nut. The revolving conical center shown at C is often used for holding a pipe or tube while turning the outside. The cone is adjusted to fit into the hole of the pipe, by means of the tailstock spindle, and the opposite end is usually held in a chuck.
Particular care should be taken to preserve the accuracy of the centers of lathe arbors by keeping them clean and well-oiled while in use.
Fig. 18. Press for Forcing Arbors into Work