76 
BULLETIN P49, 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 yg- to ti 
inch in size, and should be dense and regular in shape. Diamonds suitable tor 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§ inches long and 1| inches outside diameter and carrying six diamonds, 
each about ^ inch in diameter. The other end of the steel tube carries a Xo. 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. T^-inch 
external diameter. | inch high, with a recess tj inch in depth by If inches in diameter 
in which the steel tube is soldered. Figure 3 gives a detailed new of the drill crown 
showing the various dimensions. Tn 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 11 by J by 6 inches with a yoke 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 ot brass so 
as to hold it in place, after which the crown is placed in a small jeweler's nee "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 -j-inch drill rod. turned to about 4 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 stiff er 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. 
