Improvements in or connected with Fret Sawing Machines.
Year: 1899

page_text: Date of Application, 13th June, 1899
HOT
1000
1100
4000
PROVISIONAL SPECIFICATION.
Improvements in or connected with Fret Sawing Machines.
J
We, EDWARD GODFREY BREWER, of Batcombe Lodge, Strawberry Hill, in the
County of Middlesex, Mechanical Engineer, and PERCY HERBERT STEVENS, of
4, Pope's Grove, Strawberry Hill, in the County of Middlesex, Mechanical
Engineer, do hereby declare the nature of this invention to be as follows:-
In fret sawing machines as commonly constructed the saw is secured at one end
to an upper bar carried on guides above the table, as as to be capable of rectilinear
reciprocation, the lower end of the saw being secured to and carried by a similar
lower bar also carried in guides 'arranged below the table. The lower bar is
pivotted to a connecting rod which extends to the pin of a crank carried by the
imotor shaft of the machine, and by which the lower bar is reciprocated.
In such fret saw machines it is necessary to maintain the saw in tension
during its motions, and to this end a bow spring, commonly made of lance-wood
has been fixed to the frame above the upper bar, the latter being connected to
the ends of the bow by straps. With this device there are in practice several
defects, thus, the saw although it may always be held in tension, yet the degree
of tension varies throughout each stroke, that is, at the top of the stroke the
tension is less than at the bottom of the stroke when the bow spring is more
bent, whereas it is highly important to the effective action and economy of.the
machine that the saw should be held at an even tension throughout its stroke.
Moreover the construction of machine before mentioned produces an unequal
or irregular action of the driving crank, it having less work to perform when
passing over the top than when at the bottom of its travel.
L
It has been proposed to employ helical metal springs in tension, instead of
the bow spring aforesaid, and with such a construction a cross head has been
fixed on the lower bar, the cross head being connected by helical tension springs
to a fixed part of the frame. Such lower helical springs have not however
affected or improved the varying tension of the saw, as the lower bar is in rigid
connection with the crank through the connecting rod, but the office of such
lower springs have acted to partially counterbalance the unequal work of the
crank.
Now the object of this present invention is to provide improved mechanism
whereby the saw shall be held in constant and equal tension throughout the
whole of its stroke.
According to our invention, we connect the upper reciprocating bar to a pivot
pin upon which two links are articulated; these links extend upon opposite
sides of the sliding bar and at an angle thereto less than a right angle, the outer
end of each link being connected to a slide.
These slides are connected together by a helical tension spring, so that the
latter forms the base of a triangular figure, and the links the sides thereof, while
the bar is connected to the apex at the point where the links are jointed together.
By this arrangement the spring would be at its greatest tension, when the
saw was at the lowest part of its stroke, but the angle of the links would then

page_text: be such as to lessen the upward tension upon the saw, while as the latter arrives
iowards the top of its stroke, the angle between the links would become altered
and have the effect of compensating for the lesser tension of the spring caused
by its contraction and thus by a proper regulation of the lengths of the links,
relatively to the strength of the spring connecting their lower ends, we are
enabled to produce a practically even tension upon the saw at all points of its
stroke.
Just such an arrangement of compensating links and spring, is or may be
applied to the lower reciprocating bar to which the lower end of the saw is
attached, the link and spring device being in an inverted position.
In such a link arrangement the tension spring may be replaced with com
pression springs to act on the slides.
By this arrangement we are enabled not only to maintain a constant and
equal tension upon the saw throughout its travel, but also to produce an even
resistance on the crank shaft throughout the complete revolution.
Dated this 18th day of June 1900.
BREWER & SON,
London and Leeds, Agents for the Applicants.
We, EDWARD GODFREY BREWER, of Batcombe Lodge, Strawberry Hill, in the
County of Middlesex, Mechanical Engineer, and P'ERCY HERBERT STEVENS, of
4, Popes Grove, Strawberry Hill, in the County of Middlesex, Mechanical
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:-
In fret sawing machines as commonly constructed the saw is secured at one end
to an upper guide bar carried on guides above the table, so as to be capable of
rectilinear reciprocation, the lower end of the saw being secured to and carried
by a similar lower guide bar also carried in guides arranged below the table.
The lower bar is pivotted to a connecting rod which extends to the pin of a crank
carried by the motor shaft of the machine, and by which the lower guide bar is
reciprocated.
In such fret saw machines it is necessary to maintain the saw in tension
during its motions, and to this end a bow spring, commonly made of lance-wood
has been fixed to the frame above the upper bar, the latter being connected to
the ends of the bow by straps. With this device there are in practice several
defects, thus, the saw although it may always be held in tension, yet the degree
of tension varies throughout each stroke, that is, at the top of the stroke the
tension is less than at the bottom of the stroke when the bow spring is more
bent, whereas it is highly important to the effective action and economy of the
machine that the saw should be held at an even tension throughout its stroke.
Moreover the construction of machine before mentioned produces an unequal
or irregular action of the driving crank, it having less work to perform when
passing over the top than when at the bottom of its travel.
It has been proposed to employ helical metal springs in tension. instead of
the bow spring aforesaid, and with such a construction a cross head has been
fixed on the lower bar, the cross head being connected by helical tension springs
to a fixed part of the frame. Such lower helical springs have not however
affected or improved the varying tension of the saw, as the lower bar is in rigid

page_text: connection with the crank through the connecting rod, but the office of such
lower springs have acted to partially counterbalance the unequal work of the
crank.
Now the object of this present invention is to provide improved mechanism
whereby the saw shall be held in constant and equal tension throughout the
whole of its stroke.
In order that our invention may be readily understood we will describe same
by way of example with reference to the accompanying drawings wherein Fig. 1
is a sectional front elevation shewing so much of a fret sawing machine as will
be necessary for the purposes of this specification and Fig. 2 is a sectional plan
view of a portion of the mechanism immediately below the work table.
In the construction of machine in part illustrated, A is the work table sup
ported on a frame B which carries a guide bearing C for the reciprocating lower
guide bar D, the latter being as usual pivotted to one end of a connecting rod E,
the lower end of which is jointed to a disc or other crank F, on a shaft F. The
shaft F is carried in suitable bearings on the frame B and is driven by pulley
or in any other convenient manner.
The head G of the machine may as shewn be composed of a beam fixed to some
suitable structure, and serves to carry the upper reciprocating guide bar H, in a
guide bearing J, upon the head G. The saw K is secured by its ends in the
guide bars D and H.
According to our invention we joint upon a pivot pin on the upper end of the
upper guide bar H, two links L L', or in the case illustrated two parallel pairs
of such links, and these links extend upon opposite sides of the guide bar H and
at an angle thereto less than a right angle, the outer ends of each pair of links
being respectively connected to slides M M¹.
These slides Al Mare capable of lateral motion upon stationary guide
rails N N', carried by the framework, and may be of any approved construction;
in the construction shewn, each slide M M is fitted with a roller to run on the
rails N N', and has an extending rod passing through a bearing block at the
extremity of each rail.
The slides are caused to have a tendency to close together, towards the guide
bar H, by means of spring pressure, such spring pressure being so arranged that
it is greatest when the upper guide bar H is at the lowest part of its stroke.
In the construction shewn this is carried out by applying a helical tension
spring between the outer ends of the guide rods of the slides M M', so that
the spring forms the base of a triangular figure, and the links L L the sides
thereof, while the bar H is connected to the apex at the point where the links
are jointed together.
By this arrangement the spring would be as aforesaid at its greatest tension,
when the saw was at the lowest part of its stroke, but the angle of the links
would then be such as to lessen the upward tension upon the saw K, while as
the latter arrives towards the top of its stroke, the angle between the links would
become altered, and have the effect of compensating for the lesser tension of
the spring caused by its contraction, and thus by a proper regulation of the
lengths of the links, relatively to the strength and length of the spring connect-
ing their lower ends, we are enabled to produce a practically even tension upon
the saw at all points of its stroke. Obviously other positions may be selected
for locating the spring P, and the springs may act in compression, as for example
a spring may be placed upon the guide rod of each slide M M¹, between the
slide head and the guide rod bearing upon the end of the rail.
Just such a similar arrangement of compensating links L L' and spring or
springs, is applied to the lower reciprocating bar D to which the lower end of
the saw is attached, the link and spring device being in an inverted position,
similar parts being lettered with the same letters of reference employed in
describing the arrangement for the upper guide bar H.
By this arrangement we are enabled not only to maintain a constant and

page_text: equal tension upon the saw throughout its travel, but also to produce an even
resistance on the crank shaft throughout the complete revolution.
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. In a fret sawing machine wherein the saw is carried between two rectilinearly
reciprocating guide bars one of such being pivotted to a connecting rod operated
by a crank for giving motion to the said guide bar; pivotting at the end of the
upper guide bar two links, the latter extending laterally at an angle-thereto, and
in opposite directions, the opposite ends of the links being each pivotted to a
slide, each slide travelling on a lateral stationary guide rail, and a spring or
springs tending to force the slides towards each other, whereby the varying
angles of the links relatively to the guide bar compensate for the varying tension
of the spring or springs, in combination with a similar compensating device
applied in an inverted position to the opposite guide bar, substantially as
described.
2. In a fret saw machine the arrangement of compensating device combined
and acting substantially as and for the purposes as described.
3. The arrangement and combination of parts composing the improved balanced
fret sawing machine, constructed and acting substantially as described with
reference to the accompanying drawings.
Dated this 13th dov of Vouch 1000
BREWER & SON,
London and Leeds, Agents for the Applicants.