| 131 | 132 | 133 | 134 | 135 | 136 |
Fig. 131. Plug-Cutter. Fig. 132. Center-Bit. Fig. 133. Foerstner Auger-Bit. Fig. 134. Expansive-Bit. Fig. 135. Reamer. Fig. 136. Rose Countersink. |
Gimlets and drills are alike in that they cut away material, but unlike in that the cutting edge of the gimlet is on the side, while the cutting edge of the drill is on the end.
Twist-drills, Fig. 126, are very hard and may be used in drilling metal. They are therefore useful where there is danger of meeting nails, as in repair work. Their sizes are indicated by a special drill gage, Fig. 220, [p. 116].
Twist-bits, Fig. 127, are like twist-drills except that they are not hard enough to use for metal. Their sizes are indicated on the tang in 32nds of an inch. Both twist-bits and drill-bits have the advantage over gimlet-bits in that they are less likely to split the wood.
Twist-bits and twist-drills are sharpened on a grindstone, care being taken to preserve the original angle of the cutting edge so that the edge will meet the wood and there will be clearance.
German gimlet-bits, Fig. 128, have the advantage of centering well. The size is indicated on the tang in 32nds of an inch. They are useful in boring holes for short blunt screws as well as deep holes. They cannot be sharpened readily but are cheap and easily replaced.
Bit-point drills, Fig. 129, are useful for accurate work, but are expensive.