The two examples which follow illustrate formal and informal analysis, the first one classifying rock drills thoroughly, and the second very informally discussing some odds against Shakespeare.
Hammer drills may be classed under several heads, as follows: (1) Those mounted on a cradle like a piston drill and fed forward by a screw; (2) those used and held in the hand; and (3) those used and mounted on an air-fed arrangement. The last two classes are often interchangeable.
Mr. Leyner, though now making drills of the latter classes, was the pioneer of the large 3-inch diameter piston machine to be worked in competition with large piston drills. The smaller Leyner Rock Terrier drill was brought out for stopping and driving; it could not, apparently, compete with machines of other classes.
When the drills are thus divided we have:
1. Cradle drills--Leyner, Leyner Rock Terrier, Stephens Imperial hammer drills and the Kimber.
2. Drills used only with air feed--Gordon drill and the large sizes of the Murphy, Little Wonder, and others.
3. Drills used held in the hand or with air feed--Murphy, Flottman, Cleveland, Little Wonder, Shaw, Hardy Nipper, Sinclair, Sullivan, Little Jap, Little Imp, Traylor, and others. Again, they may be divided into those that are valveless, with the differential piston or hammer itself acting as a valve. The Murphy, Sinclair, Little Wonder, Shaw, Little Imp, Leyner Rock Terrier, and Kimber drills belong to this class. The large Leyner drill is worked by a spool valve resembling that of the Slugger drill; the Flottman by a ball valve; the Little Jap by an axial valve; the Gordon drill, by a spool valve set at one end of the cylinder at right angles to it; the Waugh and Sullivan drills by spool valves set in the same axial line as the cylinder; the Hardy Nipper, and the Stephens Imperial hammer drills by an air-moved slide-valve set midway on the side of the cylinder; the Cleveland by a spool set towards the rear of the cylinder.
They may again be divided into those drills in which the piston hammer delivers its blow on the end of the steel itself. A collar is placed on the drill to prevent its entering the cylinder. The other class has an anvil block or striking pin. This anvil block fits into the end of the cylinder between the piston and the steel. It receives and transmits the blow, and also prevents the drill end from entering the cylinder.[36]