IMPROVEMENTS IN MA- CHINERY FOR CUTTING DOVETAILS
Year: 1872

page_text: LETTERS PATENT to William Tighe Hamilton, of Rathmines, Dublin,
Ireland, Gentleman, for the Invention of "IMPROVEMENTS IN MA-
CHINERY FOR CUTTING DOVETAILS."
Sealed the 1st April 1873, and dated the 11th December 1872.
PROVISIONAL SPECIFICATION left by the said William Tighe
Hamilton at the Office of the Commissioners of Patents, with his
Petition, on the 11th December 1872.
I, WILLIAM TIGHE HAMILTON, of Rathmines, Dublin, Ireland,
Gentleman, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN MACHINERY FOR CUTTING DOVETAILS," to be as follows:-
The object of this Invention is to cause a revolving circular saw to
swing to and fro, so as to cut wedge-form spaces out of any object
suitably offered to it.
The improved machine is thus constructed :-An axle is mounted in
bearings so as to be free to reciprocate as it rotates. A portion of this
axle is cranked at such a degree of obliquity to its central line as is

page_text: necessary to produce the angle of the dovetails. This central line inter-
sects that of the cranked portion or cranked pin at the middle point of the
latter. Upon this crank pin a sleeve shaft is mounted so as to be free to
revolve on it when kept in position by suitable collars or nuts. Two
opposite sides of this sleeve shaft are flattened, and a circular boss having
a hole through it (in the line of its axis) corresponding with the flattened
shape of the shaft is mounted on it by means of pivots or gimbals which
pass through such flattened sides, so that the boss may swivel on the
shaft. For this purpose freedom is made at the other two sides of the
hole through the boss. The line of the pivots is through the middle
point of the crank pin, and in the same plane as the central lines of the
crank pin and axle. A. flanged hoop or strap carrying a circular saw is
mounted on the boss, so as to revolve on it when kept in position by two
plates fixed to its ends, and when carried round by a suitable driver
fixed upon the axle. One of these plates is shaped into a guide bar,
which extends beyond the circumference of the saw, and there carries a
block at right angles to the plate. This block works in a slot made in a
frame which is so mounted on a head concentric with the axle that the
slot shall be always parallel to the axle. The frame turns through a
quadrant, so as to be fixed either when a line through the slot and axle
is horizontal, or when such line is vertical. Thus, the action of the block
and slot upon the guide bar will maintain the saw in planes which inter-
scct in a vertical line through the axle when the axle and slot line is
horizontal, but in a horizontal line through the axle when such axle and
slot line is vertical. These positions are attained by moving the slot
frame through its quadrant. Then, when the axle is caused to rotate by
any of the usual means, the crank pin as it turns in the sleeve shaft
compels the saw hoop and the saw to swing to and fro as it revolves in
continually varying planes which intersect, as above described. Then,
if a board or other object is moved up to the face of the saw opposite to
the slot, and the slot and axle line is horizontal, a mortise or tail will be
cut; whilst, if it be moved endwise on towards the axle, and the slot and
axle line is vertical, a space will be cut in the form of a double cone,
which, when modified, as will presently be explained, will become the
interval between two tenons or pins.

page_text: applied for Letters Patent, the 7th day of December instant, is
mounted on the axle, so that its inclination when at its extreme position
may be opposite to that of the saw when at its extreme position. The
throw thus obtained for the axle will proportionally counteract the sweep
of the cutting portions of the saw. The intersection of its varying planes
will no longer be in a line which passes through the axle, but in a
parallel line at any desired distance in front of the axle for cutting tails,
or above the axle for cutting pins. Thus, all desired sizes can be
obtained, and their mutual adjustment is effected by altering the incli-
nation of the reciprocator. Any convenient form of feeding table may
be used, having proper horizontal, vertical, and traversing movements.
As the radial motion of the saw will cause the inside or bottom of the
tails to be slightly curved, its teeth should be ranged against a flat file
or stone, and then sharpened; the saw will thus become slightly elliptic,
but a circular saw is the proper shape for pins. Therefore where very
exact work is required different saws should be used for each distinct
operation.
Instead of the above cranked axle, a straight one may be used upon
which a boss disc is mounted and fixed at the desired angle. The outer
circumference of this disc may be grooved, and a strap working in this
groove may take the place of the sleeve shaft, the rest of the construction
remaining the same. Or, again, instead of the cranked axle on the
inclined disc, the saw hoop or strap may be at once mounted on a suit-
able ball and socket or other universal joint, and the block of the guide
bar may be caused to reciprocate by being linked to the rod of a second
reciprocator also mounted on the axle. These are equivalent forms, and
will produce the same action, but the first is the most simple, and
involves the least friction.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said William Tighe Hamilton in the Great Seal Patent
Office on the 11th June 1873.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
TIGHE HAMILTON, of Rathmines, Dublin, Ireland, Barrister-at-Law,
send greeting.

page_text: WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Eleventh day of December, in the
year of our Lord One thousand eight hundred and seventy-two, in the
thirty-sixth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said William Tighe Hamilton, Her special
licence that I, the said William Tighe Hamilton, my executors,
administrators, and assigns, or such others as I, the said William
Tighe Hamilton, my executors, administrators, and assigns, should
at any time agree with, and no others, from time to time and at
all times thereafter during the term therein expressed, should and
lawfully might make, use, exercise, and vend, within the United
Kingdom of Great Britain and Ireland, the Channel Islands, and Isle
of Man, an Invention for "IMPROVEMENTS IN MACHINERY FOR CUTTING DOVE-
TAILS," upon the condition (amongst others) that I, the said William
Tighe Hamilton, my executors or administrators, by an instrument in
writing under my, or their, or one of their hands and seals, should
particularly describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed, and cause the
same to be filed in the Great Seal Patent Office within six calendar
months next and immediately after the date of the said Letters
Patent.
.
NOW KNOW YE, that I, the said William Tighe Hamilton, do hereby
declare the nature of my said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the Drawings here-
unto annexed, and to the letters and figures marked thereon (that is to
say) :—
The object of this Invention of " Improvements in Machinery for
Cutting Dovetails" is to cause a circular saw while in rapid rotation to
swing to and fro so as to cut wedge-form spaces out of any object suitably
offered to it.
In the accompanying Drawings are shewn various views of an
arrangement of mechanism whereby this object may be effected with
facility, precision, and despatch. Fig. 1 is a plan view of the principal
working parts of a machine for cutting dovetails; Fig. 2 is a side
elevation of the same; Fig. 3 is an end elevation; and Fig. 4 is a

page_text: horizontal section taken through the mounting of the circular saw; and
Fig. 5 is a vertical section of the same.
The improved machine is thus constructed:-An axle a is mounted in
bearings b, b, so as to be free to reciprocate endways as it rotates. A
portion of this axle is cranked at one end as at a", Fig. 2, at such a
degree of obliquity to its central line as is necessary to produce the
angle intended for the dovetails. This central line intersects that of the
cranked portion a*, or crank pin at the middle point of the latter.
Upon this crank pin a* a sleeve shaft c is mounted so as to be free to
revolve on it, when kept in position by suitable collars a³, a'. Two
opposite sides of this sleeve shaft are flattened, while the other two sides
are bevilled in both directions from the middle of the piece, as shewn at
Figures 3 and 4. A circular boss d, having a hole through it (in the
line of its axis) corresponding with the flattened shape of the sleeve
shaft c, is mounted on it by means of pivots or gimbals which pass
through it and through such flattened sides, as shewn at Fig. 5, so that
the boss d may swivel on the shaft c. For this purpose freedom is made
at the other two sides of the hole through the boss by bevilling them
off from the centre, as already explained.
The use of pivots or gimbals may be dispensed with by employing
trunnions cast in the solid upon the sleeve piece. The line of the
pivots, gimbals, or trunnions is through the middle point of the crank
pin a* and in the same plane as the central lines of the crank pin a*
and axle a. A flanged hoop or strap e, carrying a circular saw f, is
mounted on the boss d so as to revolve on it when kept in position by
the plate & on one side and the flange a fixed to its ends.. When the
hoop d is carried round by a suitable driver fixed upon the axle, the
saw of course rotates with it. The plate d¹ carries an arm g which
acts as a guide bar as it extends beyond the circumference of the saw,
and there carries a block g' at right angles to the plate d', and which
block works in a slot in the arm or frame h, as seen in Fgures 1 and 2.
The arm or frame h is so mounted on a head h* concentric with the
axle a that the slot in the arm / shall be always parallel to the axle a.
The frame
with arm h and its appendages turns through a quadrant
shewn by dots in Fig. 3, and it can be fixed by means of a set
either when a line through the slot and axle is horizontal or when
such line is vertical. Then the action of the block g¹ on the guide bar h
piece
screw

page_text: will, as it works in the slot, maintain the saw in planes which intersect
in a vertical line through the axle a when the axle and slot line is
horizontal, but in a horizontal line through the axle when such axle and
slot line is vertical. These different positions are attained by moving
the slot frame through its quadrant, as shewn by dots in Fig. 3.
The maintenance of the saw planes in the proper position may be
effected in several other equivalent ways.
The guide bar instead of carrying a block to work in a slot may carry
a lug across the circumference of the saw so that the centre of the lug
may be in line through the gimbals or trunnions, whilst an elongated 1
plate, as shewn in Fig. 5", is mounted upon the axle of the back of the
crank pin, so that the spindle can revolve in it while it carries it back-
wards and forwards. A lug upon it comes over that upon the guide
plate. These two lugs are then pivotted together, and the pivot will
become the centre of motion upon which the saw will swing, and by :
which its planes will be maintained in suitable position. This plate is
prevented from turning by a pin fixed into the head stock on which it
rides; suitable holes in this plate admit of its being placed at the proper
quadrant. Or, again, this second plate may be dispensed with, and the
guide bar (instead of carrying the aforesaid lug) may carry two flat:
wings working in slotted horns attached to the head stock, the line of
the wings being at right angles to that of the gimbals or trunnions.
In any of these cases the action will be as follows:-When the axle a
is caused to rotate by any of the usual means, such as by means of
toothed gearing or of a driving band passed round the pulley at the end
of the axle, the crank pin a* as it turns in the sleeve shaft c compels the
saw hoop e and the saw f to swing to and fro (as indicated by the dots
in Fig. 2) as it revolves in continually varying planes which intersect as
above described. Then if a board or other object be moved vertically up
the face of the saw opposite to the slot, and the slot and axle line be
kept horizontal, a mortise or tail will be cut, but if it be moved endwise
on towards the saw, and the slot and axle line be kept vertical, a space
will be cut in the form of a double cone, which when modified, as will
presently be explained, will become the interval between two tenons or
pins.

page_text: In order to effect this modification, and at the same time to obtain
any desired sizes of tails or pins, a reciprocating or endway motion must
be imparted to the axle a by means of the mechanism shewn at A, which
I call a reciprocator, and for which I have applied for Letters Patent on
the Sixth day of December One thousand eight hundred and seventy-
two. This reciprocator is mounted on the axle a at such a degree of
inclination as may give the requisite degree of throw, but so that this
inclination at its extreme position shall be opposite to that of the plane
of the saw when at its extreme position. The throw thus obtained for
the axle a will proportionally counteract the sweep of the front or
cutting portions of the saw. The intersection of its varying planes will
no longer be in a line which passes through the axle, but in a parallel
line at any desired distance in front of the axle for cutting tails, or above
or below the axle for cutting pins. Thus all desired sizes of tails and
pins can be obtained and their mutual adjustment can be effected by
altering the inclination of the reciprocator A by means of its adjusting
screws, as shewn at Fig. 2.
The mode of cutting tails or mortises may however be so modified
that they may be cut by a horizontal instead of a vertical feed, that is,
the operation may be effected by moving the board or object endwise on,
as in the case of tenons or pins, instead of passing it vertically up the
front of the saw. An arrangement to effect this object is shewn at
Figures 6 and 7.
It will be obvious that the extent of the endway motion of the axle a
caused by the reciprocator A may be made to depend either on the
degree of inclination of the reciprocator A to the axle a, or on the
distance of the stud a² from the axle. If then the reciprocator A be
fixed at the same angle of inclination as the crank of the axle, and
suitable sliding and gearing provision be made so that the stud a³ of the
reciprocator A shall be made to approach the axle at the same rate as
the table which carries the board or object towards the saw, and if it be
also provided that the operation shall be commenced with the reciprocator
at the extreme of its throw (that is, when the intersection of the saw
planes shall be where it enters the wood or near thereto), the cutting
parts of the saw will as it were expand, according as the board or object
advances, and will contract again according as it recedes, leaving a tail cut
to whatever depth the board or other object may have been advanced.

page_text: This will be more readily understood on referring to Figures 6 and 7,
where the reciprocator A is permanently fixed on the axle a at its
extreme angular position; then, in order to vary or lengthen and shorten
the endway motion of the axle a the stud is connected to a sliding
piece t, which is capable of moving in guides in the frame, so that by
drawing down the stud a*, as shewn at Fig. 7, the endway motion of the
axle a will be correspondingly shortened, and this will necessarily affect
the action of the saw on the cranked end of the shaft to such an extent.
that whereas the edge of the saw at the point 1 in Fig. 6 always travelled
through this point while the stud a* of the reciprocator is at its highest 1
point, the edge of the saw would have a reciprocating motion when the
stud is moved down as at Fig. 7, and would consequently cut a dovetail,
as shewn in that Figure.
The motion of the stud a² and its action on the saw may be made
automatic by connecting the piece t by means of a lever to the feeding 1
table.
Any convenient form of feeding table may be used for either of these
two modes of operating, provided it has proper horizontal, vertical, and
traversing movements. These parts are not shewn, because they form
no portion of the present Invention.
A similar result will follow for cutting tails by a horizontal feed if the
stud be placed in front of the axle instead of at its back, and made to
move in along with the table; but in this case the inclination of tho
reciprocator at its extreme position must be the same and not opposed to
that of the planes of the saw at its extreme position. They must in this
case always be parallel to each other.
Whenever the line of intersection of saw planes is moved through a
quadrant so as to change from the vertical to the horizontal or vice versa
it will be necessary to effect an equivalent change as to the reciprocator.
Its extreme position must always agree with the extreme plane of the
saw, that is, each must be at its extreme inclination at the same time.
For this purpose the stud may be so mounted as to be carried round
through a similar quadrant as the block and slot as shewn at Fig. 1, or
the reciprocator itself may be so mounted upon a sleeve shaft as to turn
through a like quadrant on the axle as desired, and there be fixed by set
screws.
Or the form of reciprocator may be used which consists of a

page_text: strap and rod revolving on a crank pin such as that above used for the
sleeve piece, and a shank on this crank pin may be passed into a collet
hole at the other extremity of the axle so as to turn within it, and be
fixed by set screws in any convenient way at the desired quadrant.
As the radial motion of the saw will cause the inside or bottoms of the
tails to be slightly curved, its teeth are ranged to a straight line when
swinging to and fro against a flat file or stone, and then sharpened; this
is not requisite for cutting pins. For these the saws should be perfectly
circular; therefore where very fine and exact work is required a distinct
saw should be used for cach distinct operation.
Instead of the above cranked axle a straight one may be used carrying
on it a boss at the like angle as that of the crank. A strap is then fitted
to revolve upon this boss when kept in position by end plates. This
strap takes the place of the sleeve piece with its gimbals or trunnions,
and the rest of the construction remains as before. Or, again, instead of
either of these methods, the saw may be mounted on a ball and socket.
or universal joint, whilst the back plate and block are connected (by a
link) with a second reciprocator mounted on the axle, and thus derive
its swinging motion from it rather than from the agency of the crank or
inclined boss. All these are equivalent forms of construction, and
produce the same results.
Having now described my Invention of "Improvements in Machinery
for Cutting Dovetails," and having explained the manner of carrying the
same into effect, I claim as the Invention secured to me by the above in
part recited Letters Patent,-
First. The application for the cutting of wedge-shaped spaces in wood
or other substances of a circular saw, so mounted that the saw shall
swing to and fro in planes passing through a vertical diameter for cutting
tails, or through a horizontal diameter for cutting pins, as herein set
forth, the mounting of the saw being in fact upon an arrangement of
parts equivalent to a universal joint.
Second. The application to the arrangement of mechanism above
referred to of the mechanism herein-before described, and further, for
producing a reciprocating motion for the purpose of controlling the sizes
of the wedge-shaped spaces, by causing the planes of the saw to intersect
in other lines those that pass through the centre of the axle.

page_text: Third. The use of a guide plate with either a back block working in a
slot, or of two lugs pivotted over the centre of motion, or of wings
working in slotted appendages attached to the head stock for the purpose
of maintaining the plane of the saw in proper position.
In witness whereof, I, the said William Tighe Hamilton, have
hereunto set my hand and seal, the Sixth day of June, in the
year of our Lord One thousand eight hundred and seventy-three.
W". TIGHE HAMILTON. (L.S.)