76 BULLETIN M9, U. S. DEPARTMENT OF AGRICULTURE. 



65. THE MANUFACTURE AND USE OF LABORATORY DIAMOND CORE 



DRILLS. 



Black carbons or diamonds used for laboratory drills should range from xe to ts 

 inch in size, and should be dense and regular in shape. Diamonds suitable for the 

 work will weigh in the neighborhood of 0.1 carat each and from six to eight diamonds 

 are required for a 1-inch drill. They may be obtained from any of the diamond 

 importers. 



The diamond drill consists of a bronze crown soldered to the end of a seamless steel 

 tube about 4 h inches long and 1} inches outside diameter and carrying six diamonds^ 

 each about tj inch in diameter. The other end of the steel tube carries a No. 2 Morse 

 taper hollow drill shank through which water is admitted to the inside of the drill. 

 The drill crown proper is made of Tobin bronze, 1-inch internal diameter, l-g^-inch 

 external diameter, \ inch high, with a recess A inch in depth by 1\ inches in diameter 

 in which the steel tube is soldered. Figure 3 gives a detailed view of the drill crown 

 showing the various dimensions. In figure 36 are shown the various pieces of appara- 

 tus used in the operation of setting the diamonds in the drill crown. A is a piece of 

 cold-drawn steel \\ by $ by 6 inches with a yoke C and thumbscrew and is used to 



Fig. 36.— Apparatus used in manufacture of diamond drill. 



hold the drill crowns. After mounting a crown in the clamp as shown, six holes are 

 drilled in the face of the crown at equal distances apart, three of the holes almost 

 breaking through the outside of the face of the ring and three almost breaking through 

 the inside of the face. The holes should be slightly smaller than the diamonds which 

 are to be used, and each should be slightly nicked on the thin edge with a fine file. 

 A diamond is now placed in one of the holes, gently tapped with a piece of brass so 

 as to hold it in place, after which the crown is placed in a small jeweler's vice "D " 

 having jaws of soft steel or brass and with which the diamond is forced into the hole. 

 Should the diamond not stand the pressure and crumble, it is not fit for drilling and 

 should be used for other purposes. It should be possible to force any diamond good 

 enough for drilling purposes into a hole in the above manner. Flat drills B, made 

 of i-inch drill rod, turned to about \ inch long and of a size slightly smaller than the 

 diamonds, are used for drilling the holes. It has been found that the flat drills are 

 better than twist drills for they are stiffer and do away with a center punch. After 

 the diamonds are all set, the drill is soft soldered to the end of the steel tube and is 

 then ready for use. 



