Drill Jigs Principles of Design Machinery ... - Evenfall Studios

24 No. sDRILL JIGS
and a gage 2^ inches long placed as shown in Fig. 36, and when so
placed is ready for drilling. The third hole requires three new gages,
since it is 1 inch off the line of the other two holes, as shown in Fig. 37.
For holes which are to be finished 3/16 inch to % inch in diameter,
use first a small drill, size No. 52 to No. 30. After the holes are all
drilled to this size, then enlarge them, by the use of a series of four
lip counterbores, to the required size. Where extreme accuracy is
required, in the place of the counterbore, a small boring bar may be
substituted and the holes bored to the size desired. One disadvantage
of using a boring tool is that it requires a hole in the table equal to
the largest hole to be bored out, or that the plate shall be kept clear
of the table by blocking up with parallel strips under it.
G-
Induttrial /'/, N.Y.
Fig. 36. Plate in Position for Drilling- Second Hole
Fig. 38 shows a form of boring tool which will be found very convenient
for use on this kind of work. It consists of the shank, A,
which is fitted to the taper hole in the spindle, and a split holder, B,
which is pivoted to the shank at C, and is locked to it at D, the screw
at D serving to clamp the boring tool, E, at one end, while F clamps
It at the other end. Adjustment is obtained by swinging the holder,
the radial slot, G, allowing it to have quite a range, and the top screw,
IT, permitting fine adjustment. Split bushings in the holder will allow
the use of boring tools of smaller diameter if desired.