Fig. 889.
When a number of pieces are to be bored with their holes of equal diameters and of the same distance apart, the chucking should be performed as in [Figs. 888] and [889]; one and the same end of each link should be bored and faced, the links being held by the stem, placed on parallel pieces with plates. A pin such as shown in [Fig. 889] should then be provided, its diameter across a being a close sliding fit into the bores of the links; while the length of a should be slightly less than the length of the hole in the link, the part d should be made to accurately fit the hole bored by any suitably sized reamer; a washer b should be provided, and each end should be threaded to receive nuts. There should then be provided in the chuck plate a hole whose distance from the centre of the chuck must exactly equal the distance apart the holes in the links are required to be, and into whose bore the end d of the pin shown in [Fig. 889] must drive easily. The pin should be locked in this hole by a nut as shown in [Fig. 889]. The bored ends of the links may then be placed on the pin and fastened by a nut as in [Fig. 888], which will regulate the distance apart of the holes.
It is obvious that the pin may be passed through one of the radial slots in the chuck, and set the required distance from the centre, but in this case the pin would be liable to become moved in its position in the slot.
Side plates to prevent the link from moving should of course be applied as at d, d in the figure.
Fig. 890.
The whole process of the second chucking will thus consist of fastening the links on the pin, and setting the free end to the circle made to mark its location. This is done as shown in [Fig. 890], which represents the free end of a link, d is the circle marked to set the link by, and p a pointed tool held firmly in the slide rest tool post. The link is obviously set true when the dotted circle on its end face runs true, the pointer merely serving to test the dotted circle.
When, however, one or two links only require to be turned it will not pay to make the pins shown in [Fig. 888], especially if the holes of the different links vary in diameter, hence the work must be set by lines.