Improvements in Lawn Mowers.
Year: 1889

page_text: Date of Application, 16th Nov., 1889-Accepted, 21st Dec., 1889
Improvements in Lawn Mowers.
A communication from abroad by JOHN BRAUN & SONS, of the City and County of
Philadelphia, State of Pennsylvania, United States of America.
1, WILLIAM PHILLIPS THOMPSON F.C.S., M.1.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool and 6, Bank Street, Manchester, both in
the County of Lancaster, and 323, High Holborn, in the County of Middlesex, 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 is in that class of mowers in which a fixed or dead knife co-acts with
a multiple of spirally formed knives arranged to rotate around or with a central shaft,
and the immediate object is to provide a form of fixed knife that may be used until
worn out without requiring sharpening or trueing up.
In this class of machines it has been necessary heretofore to frequently remove
either the rotary or fixed knives, or both, and true up and sharpen the same, and to
readjust them relative to each other, it being absolutely necessary that said knives
should be in such perfect condition that a continuous shearing cut be attained, in
order to produce satisfactory results.
The improvement that forms one of the principal features of this invention consists
of a knife (corresponding to the fixed or dead" knife above referred to) which is so
formed and supported that it is capable of readily adjusting itself to the rotating
knives.
This result having been attained the knives may continue to cut smoothly for an
indefinite length of time without re-sharpening.
In the accompanying drawings figure 1 is a perspective view of a Lawn Mower
embodying the said invention, said mower being shown in an inverted position to
more clearly expose the knives. Figure 2 is an enlarged cross section of the fixed
knife and knife-bar, and figure 3 is a similar view illustrating a modification of said
invention. Figure 4 is also a cross section of the same parts having added thereto a
guard-plate to protect the yielding knife, and figure 5 is a top or plan view of the
elementary parts shown in figure 4.
Referring to the drawings, the letters a indicate the blades of the rotating cutter,
and the adjacent fixed knife, the latter being secured to a knife-bar e supported at
each end between the sides of the main frames of the mower. d d are the usual
traction wheels and e the draft handle. The means employed to rotate the knives a
form no part of this present invention and it is therefore thought unnecessary to
illustrate or describe said means in detail.
The simplest form of said improved fixed knife consists of a blade of sheet steel b
that is attached to the knife bar c by screws h (see particularly figures 2 and 4), said
blades being of such thickness that the edge engaging the rotary knives may spring
freely and follow readily any irregularities of such knives. The knife-bar c is bevelled
or inlined as at beneath the blade b to allow said blade a free and unobstructed
movement. This yielding blade 6 is so clamped to the knife-bar that its edge bears
quite heavily against the rotating knives and is, in practice, forced slightly downward
by said knives as they engage it, the movement of the free edge of blade b being,
theoretically, a wave motion, as said knives brush past it.
When an irregular or dull place in the rotating knives passes into contact with the
sheet metal blade b said blade, by its spring action, at once adjusts itself to such
irregularities and performs as perfect work as at those points that remain sharp and
regular.

page_text: In the modification illustrated in figure 3 the same desirable result is attained with
a non-elastic knife that is hinged to the knife-bar c. The cutting edge of said knife
is forced upward into engagement with the rotating knives by springs k seated in the
knife-bar and pressing constantly in the rear of the hinge pintle. Said springs act
automatically and forcibly to hold the cutting edge of said knife b¹ in close engage-
ment with the rotating knives and cause said edge to adjust itself to irregular places,
as above described in connection with the spring-plate b. With a fixed plate of
yielding form substantially as described, no sharpening or repairing of the blades is
necessary unless they are actually broken or notched by contact with stones or other
hard substances.
Heretofore in mowers of this class the fixed or dead knives have been of a thickness
fully equal to No. 14 standard wire gauge, which provides practically a rigid or non-
yielding knife. Under this present system of yielding or flexible knife, sheet steel as
thick as No. 16 wire gauge may be used although it is advisable to use much thinner
steel to insure an easy and free flexion of said knife.
When a very thin sheet metal knife is used it is sometimes desirable to protect said
knife, so that stones, sticks, bones and like articles, may not come into direct contact
with said knife and bend or break it. To meet this desideratum a guard-plate or
bar is provided as illustrated in the drawings, said guard-plate being made
preferably of cast metal and of such design that it combines strength with the least
possible weight. This guard-plate f projects toward, and nearly to, the free edge of
the yielding knife-blade b, but is backed off or bevelled on the side that confronts the
said blade, as at f2, so that said blade may be sprung or deflected a considerable
distance without coming into contact with the rigid guard-plate. This construction
protects the thin blade b yet leaves it quite free to perform its particular duty in
connection with the rotating spiral knives.
Said guard-plate is secured in place by screws or bolts ¹ that pass through both it
and the knife b and are tapped into the rigid cross-bar c.
Having now particularly described and ascertained the nature of the said inven-
tion, 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. In Lawn Mowers a fixed knife having a yielding or flexible cutting portion
adapted to co-operate with the rotary knives as set forth.
2. In combination with a rotary cutter having spiral knives, a shearing knife-blade
substantially parallel with the axis of said cutter; said blade being formed as a sheet
metal plate whose edge may yield to follow irregularities in the cutting edge of said
rotary cutter, as set forth.
3. In combination with a fixed knife-bar, and a yielding knife attached thereto as
described, a guard-plate secured below, and adjacent to, said yielding knife; sub-
stantially as specified.
4. In combination with the yielding knife and its fixed support, a guard-plate
secured adjacent to said yielding knife and having the face that confronts the said
yielding knife bevelled, as and for the purpose specified.
Dated this 15th day of November 1889.
WM. P. THOMPSON,
Agent for the Applicant.