An Improved Percussive Tool to be Worked by Pneumatic Power, and Applicable as a Dental Mallet and for other Purposes.
Year: 1888

page_text: Date of Application, 16th Aug., 1888
Complete Specification Left, 15th May, 1889-Accepted, 22nd June, 1889
PROVISIONAL SPECIFICATION.
An Improved Percussive Tool to be Worked by Pneumatic Power,
and Applicable as a Dental Mallet and for other Purposes.
We, FREDERICK EDWARD THOMAS, of 7 Jesus Lane, Cambridge, Philosophical
Instrument Maker, and ROBERT PROUDFOOT LENNOX of 59 Corpus Buildings,
Cambridge, Mechanical Dentist, do hereby declare the nature of this invention to be
as follows:
This invention has for its object an improved percussive tool to be worked by
pneumatic power and applicable as a dental mallet and for other purposes.
In the improved tool there are two cylinders and in these cylinders two pistons
work. The pistons are on the same rod and one extremity of the rod forms a hammer
and strikes blows in rapid succession upon a moveable anvil or part carrying the
instrument or plugger by which the work is done.
Between the two cylinders there is a chamber in which a valve works and this valve
controls the admission of air to the cylinders, allowing it to enter first one cylinder
and then the other.
This chamber is in constant communication by a flexible tube with a bellows from
which air is constantly supplied. Or air under a pressure suitable to the work to be
performed may be otherwise supplied.
The outer ends of the cylinders are constantly open and the pistons are not a close
fit in the cylinders or else a small passage is formed in each so that the air is able
gradually to pass from the inlet end of the cylinder to the outlet.
The valve surrounds the piston rod and is able to slide freely upon it; at its ends
are discs which at the proper times cover and close the admission apertures in the
cylinder ends. The valve is moved by means of springs coiled around the piston rod
one on either side of the valve.
The operation is as follows: supposing the pistons to be at their greatest distance
from the anvil, the valve will be open to admit air to the cylinder next the anvil; the
air acts upon the piston in this cylinder and driving it forward strikes the blow.
Meanwhile the valve is closed against the admission of air to the other cylinder and
the pressure of air in the valve chamber keeps it closed against the lighter pressure of
air confined within this cylinder which air during the stroke passes the piston and
escapes.
As the stroke is completed one of the springs surrounding the piston rod strikes the
valve and reverses its position. At the same time that this takes place the blow is
struck upon the anvil. The return stroke is then made in a similar manner except
that there is no anvil to arrest the movement of the pistons but their momentum is
expended upon the spring. The spring which operates in the return stroke is longer
than the other and admits of compression through a suitable range; its reaction aids
in propelling the pistons for the effective stroke.
The speed of working may be adjusted by varying the size of the perforations in
the pistons; the tool may if desired be so set as to give a rapid and heavy blow and
a slow return. The speed may also be varied by altering the length of stroke and the
pressure of the air. The flexible pipe which supplies the air is connected at the end
opposite to the anvil and passages convey the air to a cylindrical casing surrounding
the cylinder and communicating with the valve chamber.
Sometimes we suppress the outlet aperture at one end of the apparatus and use a
hollow piston rod. The air exit is then at one aperture only and at this we provide a
valve which can be opened and closed at pleasure; when it is closed the tool ceases to
work.
In some cases we provide a fixed stop or abutment to receive the blow of the

page_text: hammer when it is not desired that the anvil or moveable part carrying the instrument
or plugger should be struck. We apply a spring in connection with the anvil in such
manner as to press it forward away from the hammer and the hammer then strikes on
the fixed stop and only reaches the anvil when by pressure exerted by the operator
with the point of the instrument or plugger the spring is compressed and the anvil is
caused to recede until it comes within range of the hammer.
Dated this 16th day of August 1888.
CARPMAEL & Co.,
Agents.
COMPLETE SPECIFICATION.
An Improved Percussive Tool to be Worked by Pneumatic Power,
and Applicable as a Dental Mallet and for other Purposes.
We, FREDERICK EDWARD THOMAS of 7 Jesus Lane Cambridge, Philosophical
Instrument Maker and ROBERT PROUDFOOT LENNOX of 59 Corpus Buildings
Cambridge Mechanical Dentist do hereby declare the nature of this invention and
in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement:-
This Invention has for its object an improved percussive tool to be worked by
pneumatic power and applicable as a dental mallet and for other purposes.
In the improved tool there are two cylinders and in these cylinders two pistons
work. The pistons are on the same rod and one extremity of the rod forms a hammer
and strikes blows in rapid succession upon a moveable anvil or part carrying the
instrument or plugger by which the work is done.
Between the two cylinders there is a chamber in which a valve works and this
valve controls the admission of air to the cylinders allowing it to enter first one
cylinder and then the other.
This chamber is in constant communication by a flexible tube with a bellows from
which air is constantly supplied. Or air under a pressure suitable to the work to be
performed may be otherwise supplied.
The outer ends of the cylinders are constantly open and the pistons are not a close
fit in the cylinders or else a small passage is formed in each so that the air is able
gradually to pass from the inlet end of the cylinder to the outlet.
The valve surrounds the piston rod and is able to slide freely upon it, at its ends are
discs which at the proper times cover and close the admission apertures in the cylinder
ends. The valve is moved by means of springs coiled around the piston rod one on
either side of the valve.
The operation is as follows:-supposing the pistons to be at their greatest distance
from the anvil, the valve will be open to admit air to the cylinder next the anvil, the
air acts upon the piston in this cylinder and driving it forward strikes the blow.
Meanwhile the valve is closed against the admission of air to the other cylinder and
the pressure
of air in the valve chamber keeps it closed, against the lighter pressure
of air confined within this cylinder which air during the stroke passes the piston and
escapes.
As the stroke is completed one of the springs surrounding the piston rod strikes the
valve and reverses its position. At the same time that this takes place the blow is
struck upon the anvil." The return stroke is then made in a similar manner except
that there is no anvil to arrest the movement of the pistons but their momentum is
expended upon the spring. The spring which operates in the return stroke is longer
than the other and admits of compression through a suitable range, its reaction aids in
propelling the pistons for the effective stroke.
The speed of working may be adjusted by varying the size of the perforations in
the pistons, the tool may if desired be so set as to give a rapid and heavy blow and a
slow return. The speed may also be varied by altering the length of stroke and the
pressure of the air. The flexible pipe which supplies the air is connected at the end

page_text: Figure 4 is a section on the line Y Y (Figure 2).
Figure 5 is a section on the line Z Z (Figure 2).
Figure 6 is a side elevation of one of the parts.
A A¹ are the two cylinders in which work the pistons BB¹ which are fixed to a common
piston-rod C, the end of which strikes against the holder D which carries the tool E,
F being a spiral spring which tends to bring the parts D and E back again. G is the
valve chamber which is connected by the flexible tube H to bellows or other air forcing
apparatus not shown in the drawings. The air enters by the pipe J passes along the
radial passages K to the longitudinal passages L formed between the outside of the
cylinder A and the casing of the instrument to the valve chamber G, in which works
the valve M, sliding upon the piston rod. The valve M is actuated by the spiral
springs N N¹. When the parts are in the positions shown in Figure 2 air is being
admitted from the valve chamber G into the cylinder A' and is tending to force the
piston B¹ forward. As soon as the aperture O in the casing is opened by pushing
forward the tube P by means of the serrated thumb piece Q fixed to it the piston B¹
will move forward and the blow will be struck. Meanwhile the spring N will have been
compressed and the spring N¹ relieved so that the valve M will be shifted so as to cut
off air from the cylinder A' and admit it to the cylinder A when the reverse action
takes place, the motion continuing so long as the opening O is uncovered by the
tube, and the rapidity of the blows can be varied by more or less covering the
opening O.
In the apparatus shown in the drawings the piston rod is made hollow so that
the air from the cylinder A as well as that from the cylinder A¹ escapes through the
opening O.
As shown the piston B₁ forms a nut upon the screw threaded piston rod and is
grooved as shown in Figures 2 and 5 to receive a feather upon the casing so that by
turning the casing the distance of the pistons apart can be varied.
•
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what we
claim is :-
1. The combination of two single acting cylinders whose pistons are both upon a
common rod actuating the percussive tool and a valve by which air is supplied to one
or the other cylinder, substantially as described.
2. In apparatus such as is described in the first claim-
(A) Placing the valve upon the piston rod between the two pistons and
actuating it by springs abutting against the pistons substantially as described.

page_text: (B)-Applying a spring to press the anvil forward away from the hammer in
such manner that the hammer only reaches the anvil when by pressure exerted
by the operator with the point of the instrument or plugger the spring is
compressed and the anvil is caused to recede until it comes within range of the
hammer.
(C) Making the piston rod hollow so that the two cylinders have a common
outlet.
(D) Providing means for varying the distance of the two pistons apart.
3. Percussive tools to be worked by pneumatic power substantially as described and
own in the drawings.
בד
1
1000
FREDERICK E. THOMAS.
R. P. LENNOX.