Convex Turning Attachment for Boring Mills.—[Fig. 12] shows a vertical boring mill arranged for turning pulleys having convex rims; that is, the rim, instead of being cylindrical, is rounded somewhat so that it slopes from the center toward either side. (The reason for turning a pulley rim convex is to prevent the belt from running off at one side, as it sometimes tends to do when a cylindrical pulley is used.) The convex surface is produced by a special attachment which causes the turning tool to gradually move outward as it feeds down, until the center of the rim is reached, after which the movement is inward.
The particular attachment shown in [Fig. 12] consists of a special box-shaped tool-head F containing a sliding holder G, in which the tool is clamped by set-screws passing through elongated slots in the front of the tool-head. In addition, there is a radius link L which swivels on a stud at the rear of the tool-head and is attached to vertical link H. Link L is so connected to the sliding tool-block that any downward movement of the tool-bar I causes the tool to move outward until the link is in a horizontal position, after which the movement is reversed. When the attachment is first set up, the turning tool is placed at the center of the rim and then link L is clamped to the vertical link while in a horizontal position. The cut is started at the top edge of the rim, and the tool is fed downward by power, the same as when turning a cylindrical surface. The amount of curvature or convexity of a rim can be varied by inserting the clamp bolt J in different holes in link L.
The tools for machining the hub and sides of the rim are held in a turret mounted on the left-hand head, as shown. The special tool-holder A contains two bent tools for turning the upper and lower edges of the pulley rim at the same time as the tool-head is fed horizontally. Roughing and finishing tools B are for facing the hub, and the tools C, D, and E rough bore, finish bore, and ream the hole for the shaft.
Fig. 13. Turning a Taper or Conical Surface
Turning Taper or Conical Surfaces.—Conical or taper surfaces are turned in a vertical boring mill by swiveling the tool-bar to the proper angle as shown in [Fig. 13]. When the taper is given in degrees, the tool-bar can be set by graduations on the edge of the circular base B, which show the angle a to which the bar is swiveled from a vertical position. The base turns on a central stud and is secured to the saddle S by the bolts shown, which should be tightened after the tool-bar is set. The vertical power feed can be used for taper turning the same as for cylindrical work.
