[Fig. 419] is one illustration with an eccentric chuck on the lathe mandrel.
Fig. 419.
That my description may be complete I will now give drawings of my eccentric chuck for the upper mandrel. It requires to be constructed differently to the ordinary eccentric chuck, as the circular movement requires to be always central, and only the slide carrying the pin to receive the rod must move eccentrically.
Fig. 420, also 422.
Fig. 421, also 423.
Figs. [420] and [421], are full-size drawings of my eccentric chuck on my upper mandrel, used for producing the foregoing specimens. In this case I have preferred a wood foundation, as not being so likely to run off as metal, on reversing the motion which is sometimes necessary on account of idle wheels for the connections. I used a piece of well-seasoned Spanish mahogany, taking care that the grain of the wood was at right angles with the length of the screw of the mandrel. A piece of brass is screwed at the back to prevent the screw cutting into the wood. [Fig. 420] is a section, and [Fig. 421] a front view of the chuck, and I think all sufficiently clear. I will just say the long fine threaded screw I cut up with the stocks and dies in the lathe, using steel wire of the necessary size. This I manage easily, and keep the wire straight by allowing it to expand in length. I chuck the steel wire concentrically, and removing the centre from the back poppet, substitute a brass centre with a hole the size of the steel wire, which is allowed about a quarter of an inch entry. I then turn down a little below the depth of the intended screw thread for about half an inch in length next the back centre, to allow the dies to come back to be tightened up, and which must only be done at the commencement and not on the return motion of the dies. The collar on the screw is a piece of brass with a hole of a size to drive on the wire tight, and is then pinned on and turned up true, and finished with the division marks.