Year: 1886

page_text: I ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
Engineer do hereby declare the nature of this invention (a communication from
William Murchey of the City of Toronto, Canada, Machinist) and in what manner
the same is to be performed, to be particularly described and ascertained in and by
the following statement :-
The object of the invention is to design a tap which can be readily set to cut
any given number of threads and having done so will automatically be thrown
out of action so that the tap may be withdrawn straight out of the hole without
the necessity of unscrewing it; and it consists essentially of screw-cutters fitted
into and pivoted in slots made in a mandrel having a hole in its centre to receive
a spindle arranged to expand the cutters and adjustably connected to a cotter
extending outside of the mandrel and having an adjustable gauge which can be
readily set to come in contact with the surface of the article being screwed to
gauge the depth at which the screw-cutting shall cease and by pushing the
internal spindle clear of the pivoted cutters permit their springs to throw them out
of action substantially as hereinafter more particularly explained.
Figure 1 is an outside perspective view of this improved tap.
Figure 2 is a longitudinal section of the same.
A represents a mandrel made any required size and designed to fit into a
machine or it may be made to be operated by an ordinary hand-wrench.
B is a spindle inserted into a hole made in the centre of the mandrel A. One
end of the spindle has a thread cut on it to screw into the cotter C which passes
through the slot D made in the mandrel A immediately behind the hole into
which the spindle B is placed.
E represents the screw-cutters which are fitted into slots made in the mandrel A
and are each pivoted at a to the said mandrel.
F represents a spring which is placed below each cutter E behind its pivot a the
expansion of the springs causing the ends of the cutters E to fall in towards the
centre of the mandrel so that when the springs F are permitted to act the cutters
will be carried clear of the thread being cut thereby enabling the ready withdrawal
of the tap without the necessity of unscrewing it.
G is a head formed on top of the cotter C and fitting the outside of the
mandrel A. This head G has a hole through it to permit the passage of the gauge-
rod, H which also passes through a hole in the guide I formed upon or attached to
the mandrel A as indicated.

page_text: A set-screw J screwed into the head G provides means for holding the gauge-
rod H in any desired position.
A tapered head b is formed on the end of the spindle B and inward projections d
are formed on the end of each cutter E. When the head b is inserted between the
ends of the cutters E the said cutters are beld out as indicated in figure 1 and
when so held will cut the thread they are intended for.
In operating this improved tap I first adjust the gauge-rod H so that its end
shall come against the surface of the article being tapped about the time that
I wish to stop the cutting of the thread. The said gauge-rod is thus pushed back
and as it is connected to the cotter C as before described the said cotter is pushed
back with it and the head b of the spindle B is thereby withdrawn from between
the inward projections d on the cutter E thereby leaving the said cutters free to
be acted upon by the springs F which cause as before described the said cutters
to spring inwardly towards the centre of the spindle thereby carrying them free of
the thread just cut and enabling the tap to be pulled out without the necessity of
unscrewing it.
When the mandrel A, is connected to a drilling machine or other spindle
weighted or otherwise arranged to spring back when it has reached the end of
its stroke I provide an arrangement for reexpanding the cutters E so as to be
ready to tap the next hole. This may be accomplished by pivoting at k a lever K
or its equivalent to some stationary part of the machine, and against which the
head G strikes when the mandrel is brought back, as before mentioned. In this
way the cotter C is pushed forward and as the spindle B is attached to it the
latter's head b is pushed between the cutters E and thereby causing them to
expand as mentioned.
By screwing the spindle B into the cotter C it can be readily adjusted so that
the head b will not be pushed forward further than is necessary to expand the
cutters.
Having now particularly described and ascertained the nature of this said
invention and in what manner the same is to be performed as communicated to
me by my foreign correspondent I declare that what I claim is
1. The cutters E pivoted as described in slots made in the mandrel A and
actuated by the springs F as specified in combination with the spindle B inserted
into the mandrel A between the cutters E and connected to the cotter C sub-
stantially as and for the purpose specified.
2. The cutters E pivoted, as described in slots made in the mandrel A and
actuated by the springs F as specified, a spindle B inserted into the mandrel A
between the cutters E and connected to the cotter C in combination with the
gauge rod H adjustably connected to the head G of the cotter C substantially as
and for the purpose specified.
3. The cutters E pivoted as described in slots made in the mandrel A and
actuated by the springs F as specified in combination with the spindle B inserted
into the mandrel A between the cutters E and having a tapered head b to act
against the inward projections d formed on the cutters E substantially as and for
the purpose specified.