Improvements in Electromagnetic Percussive Tools.
Year: 1895

page_text: Date of Application, 27th Aug., 1895-Accepted, 12th Oct.. 1895
[Communicated from abroad by ABRAHAM GEORGE FONDA, Louisville,
Kentucky, U.S.A., Gentleman.]
Improvements in Electromagnetic Percussive Tools.
1, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of The Agency for
Foreign Patent Solicitors, 31, High Holborn, in the County of Middlesex,
6. Lord Street, Liverpool, and 6, Bank Street, Manchester, both in the County
of Lancaster, and Lower Temple Street, Birmingham, in the County of Warwick,
Civil Engineer, 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 relation to electro-magnetic tools or machines having a
reciprocating motion for effecting rapid intermittent blows or strokes when
influenced by an electric current, and is designed chiefly for cutting stone and
other hard substances.
In the accompanying drawing (a longitudinal section) the letter A designates a
cylinder or casing of soft iron having a rim P projecting inwardly and supporting
an iron bottom plate D, to which is connected an inner hollow or bored cylinder or
core B, of soft iron, which is surrounded by part of the coil or helix C, of insulated
wire, (the size of the wire is according to the voltage of the electric current that
is to pass through it, for instance with a current supplied at a 110 volts a
number 28 wire is suitable) forming an electro-magnet.
The cylinder
has a male screw on its lower end for the attachment of a
tubular guide J. B' represents another cylinder of soft iron, inside of cylinder A,
surrounded by part of the coil or helix C, forming another electro-magnet. F is a
central rod hammer of no magnetic power, preferably of aluminum bronze, which
moves with a reciprocating or to and fro motion through the cylinder or electro-
magnet B. Its lower end operates on the end of the anvil-piece or bit-carrier K,
the other end of the said central rod-hammer plays to and fro in a hole in the
bearing E, which aids in keeping the said rod-bammer in proper position, so that
the cylindrical armature or electro-magnet B', which is attached to the rod-hammer,
can play to and fro within the coil or helix C. I is a balancing or equipoising
spring is also a balancing and equipoising spring; I is a retracting spring
between the lower interior shoulder of the tubular guide J, and the collar k of
the anvil-piece or bit-carrier K.
Attached to the cylinder B by a screw, is the brass tubular guide J, within
which is carried the anvil-piece or bit-carrier K, having upon it a guide collar k.
This anvil piece is preferably of a cylindrical form, as is also the hammer rod, and
these parts are in axial relation to the electro-magnets or cylinders B and B. G is a
spool of non-magnetic material, arranged inside of the cylinder A, and around
the cylinders B and B on this spool is wound the coil or helix C, the ends of the
wire coming out at c, c¹.
M is a brass yoke piece to which is attached the bearing E, supporting the end
of the hammer rod F.
H is a brass cap screwing into the end of the casing A, securing all the internal
parts in proper position and allowing the passage out of the wires c and c¹, by
unscrewing and removing this cap, all the interior construction will drop out.
is a very thin disk of aluminum bronze or brass which, when the tool is in

page_text: operation, rests on the top of the cylinder B, and prevents the cylinders B and B
from coming in actual contact.
When an electric current passes through the wire c, c¹ and helix C, the
cylinders B and B₁ become powerful magnets and are attracted toward each other,
the force of the downward motion or blow is expended on the anvil-piece or bit-
carrier K, causing the same to move forward sharply in its guide in an effective
manner for working its bit or chisel in cutting stone.
When the electric current is interrupted, the cylinder B is separated from
cylinder B by the force of the spring 1', and is then in position for another
blow. The tool is therefore operated by an interrupted current of electricity.
The outer casing A, being made of iron, the cylinders B and B' surrounded by
the same helix C, and cylinder B, connected by the iron plate or yoke-piece D to
the outer casing A, allows the magnetic current or lines of force to pass freely to
nearly complete the circuit at the upper end of the tool, being as it were nearly
" iron clad ; the result is a magnetic field of greater intensity between the
cylinders B and B', consequently greater power in the tool.
In tools or machines of this character it has previously been found impossible to
get over about 1200 blows per minute, and then they would not satisfactorily cut
granite although the tool might make powerful strokes. The character, number,
and velocity of the blows were not suited for that work, and when the number of
breaks in the current exceeded about 1200 per minute, the tool ceased to work.
By using the balancing or equipoising springs I I¹, I have increased the rapidity
of the blows to over the almost incredible number of 2000 per minute, and at the
same time they have the peculiar impact blow required in working granite.
The two balancing or equipoising springs I, II may be made of the same piece
of wire, the spring I should be long enough and strong enough to move the
cylinder B until it is almost in contact with cylinder B when the tool is in a
horizontal position.
The spring I should be long enough and strong enough to force back the
cylinder B against the pressure of the spring I the proper distance from the
cylinder B, which distance varies according to the electro-motive force of
the current used.
By thus balancing or equipoising the cylinder B' between two elastic forces,
I have obtained much more rapidity in action and efficiency in electro-magnetic
tools.
I am aware that various devices called "buffers" have been used to arrest the
upper end of the hammer rod F, nearly at the end of the slight blow upward from
the force of a spring that separated an armature from a magnet.
The action of these "buffers" is very limited, and that too at nearly the end
of the upward stroke, so as to take the shock of the tool.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. In an electro-magnetic tool, the combination of a fixed electro-magnet having
its extension on the outer side of the motor coil, a solenoid or motor coil, an
electro-magnet with axial hammer rod having a reciprocating motion therein, and
counterbalancing or equipoising springs, substantially as described.
2. In an electro-magnet tool, the combination of a helix, an iron exterior casing,
an iron yoke-piece, a fixed electro-magnet, and an electro-magnet held in balance,
or equipoised, between two elastic forces, substantially as described.
Dated this 27th day of August 1893.
W. P. THOMPSON & Co.,
31, High Holborn, London, W.C., Patent Agents for the Applicant.