A different cutting speed is necessary for nearly every material, and drills are constructed so as to meet the various requirements. A large drill must run slower than a small one, the turns per minute becoming less as the size of the drill increases. For example, a drill 1/2 in. in diameter should make twice as many revolutions per minute as a 1 in. drill, and four times as many as one 2 in. in diameter. For this reason, there must be a number of different feeds, as well as speeds. Hand-feeding is to be preferred to machine-feeding for small or delicate work, since it is possible to "feel" the drill and keep it going through the work at a varying rate according as the metal is hard or soft or contains blow-holes and imperfections. A heavy power-driven feed will sometimes break quickly into a blow-hole and spoil the drill or the work.
The cone pulley shown in Fig. 143b (page 288) gives three different speeds to the drill spindle and the drill. There are two cone pulleys, an upper and a lower; when the belt is on the smallest step of the upper cone pulley, the fastest speed is obtained.
The drill table generally swings about the post or upright frame of the machine, thus allowing the work to be adjusted under the spindle. Some machines are provided with tables which pull in and out in a straight line as well as swing in a circle. This straight-line adjustment allows a number of holes to be drilled in a row without swinging the table.