wrench for hand tapping, and have the pressure equal on both ends. To square up a tap, use a small steel square, as shown at a, Fig. 2. Use the square fre

quently until the tap is fairly

started. A 6-inch steel rule may be used instead of the square, as shown at b. A finished nut can be used to square a tap, as shown in Fig. 3. The tap is run through the nut into the hole to be tapped.

Tapping Jig.-In Fig. 4 is shown one form of tapping jig, consisting of a piece of steel bent to the form shown at a. The bottom surface b c is planed flat, and a hole d the size of the tap shank is drilled square to b c. A plug e is turned to fit d and the hole ƒ to be tapped. To use this jig, the plug is put into the hole d and then pushed into f, as shown; the base a is clamped fast at the point g, after being adjusted until the

(Morse Twist Drill and Machine Company)
TAP DRILLS FOR V THREADS

plug e fits easily in both holes, and the plug is removed and

replaced by a tap.

Removing a Broken

Tap.

When a tap breaks off near
the surface it can be removed
as shown in Fig. 5. A drift or
blunt cape chisel a is placed
against each side of the broken
piece of the tap b and each is
struck a light blow at the
same time, forcing the tap to
turn.

If the tap is broken below the
surface of the work, the method
shown in Fig. 6 can often be
used to remove it. A piece of

FIG. 4

steel wire is bent to a U shape, and inserted in opposite flutes A monkey wrench is then applied to the upper part of the bent wire.

of the tap.

In case the piece of tap is stuck firmly in the hole, the American Machinist recommends the following method of removing it:

FIG. 6

Use a drill the size of the tap drill, and of sufficient length to reach past the broken tap. Grind the lip of the drill as shown in Fig. 7 after which chuck the drill in a sensitive drill press and clamp the work with the piece of tap in line. Run the machine at a slow speed, and bring the drill down slowly on to the broken tap. The lips of the drill will straddle the center of the tap, and go down into the flutes. Judgment must be

FIG. 7

used as to the amount of pressure applied. The lips of the drill will cause the tap to splinter. The splinters can be removed, and the operation repeated until the entire tap has been removed. By carefully running an old tap into the hole, the fine splinters still remaining can be removed, after which a new tap can be used to complete the job.

Preventing Taps From Breaking.-It is recommended that the tap be heated at the shank end to a blue color. The shank will then begin to twist before the tap breaks, and the operator will be warned.