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Julyjel919 within extremely close limits, scale measurement being near. enough, it is obvious that the two units which are machined at one setting must be incorporated. into the finished part. Thus, the number of pieces fastened together in the machining operation must be a multiple of two. In Fig. 18, eight parts are fastened together for machining. at one setting. The valves on this engine are ac- tuated through the medium of a stephenson link motion with open rods. The link used is of the double- bar type. The valve gear is equipped with linking-up screws for the- pur- pose of altering the cutoff of any cylinder independent. of the others. Pins for the eccentric rods are riveted to the link bars while the suspension pin is a continuation of the go-ahead eccentric rod pin. -The link bars are held the required distance apart by cast iron spacers. The link bars are steel forgings. The first operation in the machine shop consists of surfacing them. This work is done on a planer of unusual type which has two housings, cross- rails, etc., facing each other. This tool is illustrated in Fig. 19. It is an economical tool as it cuts on both strokes of the platen. The link bars are held, several in a line, on the platen by pinch dogs and clamping posts. The pieces are first roughed out, leaving several thousandths of an inch on each surface for finish- ing. Finishing is done with a steel finishing tool. The next operation consists in ma- chining the holes for the eccentric trod pins, and the fillers that hold the link bars the required distance apart. These holes are drilled and reamed in a jig on a_ heavy-duty drilling machine as illustrated in Fig. 16. The link bars are drilled and reamed two at one setting. This op- eration is simple and is readily un- derstood from the illustration. After 'the link bars are drilled and reamed, the next operation consists FIG. 18--EIGHT 'WALKING BEAMS FOR AIR PUMPS FASTENED THE (MARINE *REVIEW of forming the radii over which the link block travels as the gear is hooked up. Many schemes have been devised in times past for finishing these radii but the plan followed at the Hamilton works is simple and it is productive of accurate results. Those who. understand marine en- gines appreciate the fact that the radii, in, question must be machined correctly to insure the valve -func- tioning properly. These surfaces are finished on a large boring mill and are located by means. of a fixture, strapped to the platen of the ma- chine. The fixture is equipped with locating pins. which engage the holes previously reamed in the links. Forty links are placed on the fixture and turned at one operation. Assures: Accurate Results If the operator exercises care in setting the tools for the finishing cuts, accurate results are assured. Not only will the radii be of the correct di- mensions but the turned _ surfaces will stand square with the sides of the link bars. This is essential 'as the better bearing the link bars pre- sent to the link-block gibs, the longer the unit will run without attention. Another important member of the 341 valve gear,ig.,the link block, This unit is located directly under the valve stem and is interposed between the link bars. It is machined from forged steel and finished all over. The first machining operation on this unit con- sists of turning and facing the center portion that fits the box at the end of the valve stem. In this operation, - care is exercised to see that the cen- ter portion is turned round - and straight and that the sides are faced true and square. At this setting, be- fore the piece: is taken out of the lathe, one outside face is finished. As this facing is done at the same setting in which the center portion was turned, it is obvious that it will be true and square with the turned part. This is essential, since the outer face as finished in the lathe is used as a locating point in subsequent operations. The next operation is done on the planer and consists of, finishing the flat surfaces. Several pieces are lo-- cated at one setting in a shoe as illustrated in Fig. 14. Using the flat surface that was turned as the locat- ing point in the first operation, it is an easy matter to machine all the flat surfaces square and parallel with the turned portion. This is easily ' done. TOGETHER FOR DRILLING AND REAMING