[Illustration: Fig. 22. Multiple-spindle Cylinder Boring Machine]
The holder shown to the right is attached to the face of the turret by four fillister-head screws. Sleeve _C_ is held in plate _A_ by means of two steel pins _B_ which are tight in plate _A_ and made to fit freely in bayonet grooves _D_. Reamer holder _E_ floats on sleeve _C_, the floating motion being obtained through the four steel pins _G_ extending into driving ring _F_. Two of the pins are tight in the holder _E_ and two in sleeve _C_. The faces of sleeve _C_, driving ring _F_, and reamer holder _E_ are held tightly against each other by means of spring _H_ which insures the reamer being held perfectly true. Spring _H_ is adjusted by means of nut _I_ which is turned with a spanner wrench furnished with each holder. The reamer is so held that its axis is always maintained parallel to the center of the hole, and, at the same time, it has a slight self-adjusting tendency radially, so that the hole and reamer will automatically keep in perfect alignment with each other.
=Multiple Cylinder Boring Machine.=--In automobile and other factories where a great many gasoline engine cylinders are required, multiple-spindle boring machines of the vertical type are commonly used. The machine shown in Fig. 22 is a special design for boring four cylinders which are cast _en bloc_ or in one solid casting. The work is held in a box jig which has a top plate equipped with guide bearings for holding the spindles rigidly while boring. The lower end of each spindle has attached to it a cutter-head and the boring is done by feeding the table and casting vertically. This feeding movement is effected by power and it is disengaged automatically when the cutters have bored to the required depth. The particular machine illustrated is used for rough boring only, the cylinders being finished by reaming in another similar machine. The cylinders are bored to a diameter of 3-5/8 inches, and about 3/8 inch of metal is removed by the roughing cut. The spindles have fixed center-to-center distances as the machine is intended for constant use on cylinders of one size, so that adjustment is not necessary. Of course, a special machine of this kind is only used in shops where large numbers of cylinders of one design are required continually. Some cylinder boring machines of the vertical type have spindles which can be adjusted for different center-to-center distances if this should be necessary in order to accommodate a cylinder of another size.
