The entire thread can be cut this way, which is rather slow or, after it is well started, the work can be
removed from the drill press and the thread finished by hand in the vise.
If it was necessary to move the drill-press table to remove the drill and insert the tap, make sure it is
returned to the exact position used to drill the hole. Adjust the collar on the column so the table will not
drop down and fix the turn indicator to its position, before moving the table.
If there is no turn indicator, make a chalk mark on the column. This same method of starting a tap in a
drilled hole applies to holes drilled in the lathe. In this case, the tap is placed in the tail stock chuck, and
the work is turned by hand, using a wrench on turn with and feeding with the tail stock.
Larger taps, like pipe taps, cannot be held in the drill-press chuck. These taps generally have a center
reamed in the head end, and a 60 " stub center can be set up in the drill press to line up the tap. Then
the tap is turned with a wrench on its square end. This stub center is a piece of 1/2 inch stock turned to a
60" point. It does not need to be hardened, although it would last longer if it were hard. This stub center
is very useful in locating a punch mark under the center of the drill. Set the stub center in the drill chuck
and center the work under it before clamping to the table.
Many firms supplying drills have printed cards showing the size of hole to be drilled for taps and the
clearance holes for threads. These also show the size of drills and their decimal equivalent.
Get two of these cards, one showing the tap drills and the other the decimal equivalents. Mount them on
the wall near the drill press.
Dies are used to cut external threads. The small button dies of 1-inch diameter are very handy for
threads up to 1 /2 inch, but for threads over 1/2 inch, larger dies are required. Even the button die of 1
inch for 1 /2 inch threads is so narrow that only a few teeth can cut the thread. This size is very useful for
rerunning a thread that has been damaged.
Only one die of each size is needed. One side of the die has a taper for starting and is used for cutting
the thread. The other side has the full thread clear to the face of the die, and the die can be turned this
side to the work to finish the thread up to a shoulder.
It is difficult to start a die square with the work. If it is not started square, it will try to follow its own
threads, while at the same time running off-center to the work, which tries to force it back to center. The
result is a very crooked thread. Die stocks have three adjustable fingers on the starting side.
These can be set to bear on the work and guide the Die Square. You should also have a plain diestock
to finish threads in close quarters where the stock with the guide is too wide to use.
When you purchase the dies, get the kind that is split on one side so the size can be adjusted. There are
many of these button dies sold at bargain stores that are not true to size. These can cause a lot of
trouble by cutting an over sized thread. Get dies made by one of the recognized, nationally established
firms, so you will be sure of getting good ones. It is often required to cut a thread a little under size, say,