Improvements in the Manufacture or Finishing, more Particularly of the Blades, of Screw Propellers and Apparatus therefor.
Year: 1887

page_text: Date of Application, 10th Jan., 1887
Complete Left, 8th Oct., 1887
Complete Accepted, 15th Nov., 1887
Improvements in the Manufacture or Finishing, more Particularly
of the Blades, of Screw Propellers and Apparatus therefor.
I, ROBERT PILE DOXFORD of Sunderland in the County of Durham, Engineer, do
hereby declare the nature of this invention to be as follows:-
This invention though applicable to other articles which have an uneven surface
and to various kinds of screw propellers is especially designed for forming the blades
of the propellers of torpedoes where the metal is too thin to be cast to the finished
size. These blades are usually made of steel which is so thin that at the edges it
frequently is not more than an eighth of an inch thick, consequently it being found
impracticable to cast the blades of the proper proportions they have to be forged and
hand trimmed which is a tedious and most expensive process. The apparatus I
shaping or planing
employ in carrying out my invention consists essentially in a
machine the cutting tool of which is caused to follow the path which will give to the
face of the propeller blade or other article the shape required. The salient features of
the apparatus are as follows:-
A suitable framing carries on top a sliding carriage which is caused to traverse
backwards and forwards in the manner commonly adopted for the beds of planing
machines. Upon this sliding carriage is a travelling tool carriage arranged to travel by
self acting mechanism in a path at right angles to that of the sliding carriage. At
one end of the tool carriage is a plunger to which the tool is secured preferably by a
"relief toolholder" and at the other end of the carriage is a similar plunger in the
end of which is a roller. The two plungers are so connected that any movement
imparted to one is transmitted to the other either in its original extent or modified.
Upon the sides of the framing and under the two plungers are two plates arranged
preferably with a swivelling mechanism so that their surfaces may be caused to lie in
a horizontal plane or may be inclined as may be required. These plates are so
connected that they move simultaneously. The operation is as follows:
The blade to be finished is cast considerably thicker than the finished blade is to
be and is bolted or secured to the plate which is underneath the tool plunger and a
pattern block or template representing the shape of the finished blade is secured to

page_text: the plate underneath the roller plunger; the tool carriage is adjusted so that the
roller is ready to commence traversing the template and the tool to take its first cut
on the propeller blade and the machine started. As it proceeds with its work the
roller plunger rises and falls (under the influence of weight or spring pressure)
according to the surface presented by the pattern and the same motion being
reproduced in the tool the propeller blade at the end of the operation presents a
fac-simile of the template.
As a considerable amount of rise and fall of the tool would in some cases have to be
provided for the tables are made to swivel in order that the attendant by turning both
blade and pattern together may so adjust them as the work proceeds that comparatively
very little rise and fall is needed.
Selfacting mechanism is applied to the various motions except to the adjustment
of the tables which however can if necessary be rendered selfacting also.
In the machine above described the general line of traverse of the tool is in a
horizontal plane, but I can make it in any other plane that may be found desirable
altering the disposition of the other parts as may be necessary to suit this.
A convenient means of actuating the two tables is to join them to a shaft extending
across the machine and carrying a worm segment with which gears a worm which is
turned by the attendant or automatically.
Dated this 10th day of Januar 1887

page_text: Improvements in the Manufacture or Finishing, more Particularly
of the Blades, of Screw Propellers and Apparatus therefor.
1, ROBERT PILE DOXFORD of Sunderland in the County of Durham, 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 especially designed for shaping the blades of propellors especially
those of torpedoes and torpedo boats where the metal is too thin to be cast to the
finished size or where great accuracy is required. These blades are usually made of
steel and are so thin that the edge where the metal is thinnest is frequently not more
than an eighth of an inch thick consequently it being found impossible to cast the
blades of the proper proportions they have to be forged and trimmed by hand which is
a tedious and most expensive method. By my invention I am enabled to finish the
forged blades with much greater accuracy than is possible under the old system and
besides I can use cast blades which was not before practicable and can finish these
also with the greatest accuracy.
The apparatus I employ in carrying out my invention consists essentially in a
machine the cutting tool of which is caused to follow the path which will give to the
face of the propellor blade or other article the shape required.
In the accompanying drawings: Fig. 1 represents a side elevation of a machine for
finishing propellor blades constructed according to my invention. Eig. 2 is an
elevation of the end thereof. Fig. 3 is a plan and Figs. 4, 5 and 6 are details of
the tracer or plunger which traces out the path of the tool, hereinafter fully
described.
A is a rectangular hollow frame having internal bearings A' A¹ formed on its
longer sides for the purpose of supporting a stont shaft B to which is fixed at one
end a table B' for supporting the pattern C which is a copy of the surface required to
be reproduced on the rough propellor blade, and at the other end of the shaft B is
fixed a similar table B which carries a block C to support the blade of the propellor
and also an inclined pedestal or axis C upon which the propellor can be mounted
during the operation of finishing and by the use of which I am enabled to place the
blades over the block C¹ at a constant angle. The tables B1 and B2 are each formed
with a circular segment B³ which rests against the side of the frame A and is
secured thereto around its circular edge by the overlapping segment ring A³ which
is firmly fixed to the frame A by bolts a.
This construction admits of both of the tables being revolved about the axis of
the shaft B and as this axis coincides horizontally and vertically with the axis of the
pattern C and with that of the propellor blade D when the latter is fixed in position
above the supporting block C I am enabled to change the position of the blade and
of the pattern so as to keep then in a suitable position for the tracer and the tool

page_text: to traverse. Along the upper edges of the sides of the frame A are formed guides A*
upon which moves a sliding carriage E and upon the carriage E are other guides E¹
arranged at right angles to the guides A between which guides E' moves a sliding
tool carrier F. One end of the carrier F supports the vertical cutter bar F' carrying
the cutting tool at its lower extremity and jointed at its upper end to a lever F2
which is pivotted to a link which forms a movable fulcrum and allows the cutter
bar F¹ to rise and fall vertically in its carrier. The lever F is weighted at F³ so that
it will exert the requisite pressure on the cutter bar F¹ to keep the tool f
in "cut."
The opposite end of the tool carrier F is provided with duplicates of the
parts F, F as shown at F"f" and " but instead of a cutting tool, a "tracer" G
is inserted in the end of the bar F. The adjacent ends of the two levers F', F12 are
connected by a rigid link F. It is obvious that any movement of one of the
levers F, F will be shared by the other and if the levers are of equal length the rise
and fall of the tracer will be attended with an equal rise and fall of the cutting
tool.
The operation of the parts of the machine already described is as follows:
The blades of the propellor in the first instance are as previously remarked made
thicker than the finished blades are required to be. The hub of the propellor is placed
on the short shaft or pedestal 02 and one of the blades secured upon suitable packing
to the block C which is secured upon the table B and the pattern C so adjusted
upon its table B' that the position of the tool f relatively to the blade of the propellor
shall be the same as that of the tracer G relatively to the pattern C and the path of
the point of the tool will be a reproduction of the path of the tracer and the surface
exposed by the tool after each cut will resemble in contour the corresponding portion
of the surface of the pattern which latter is preferably made of cast iron accurately
finished. The depth of the cut may be regulated by raising or lowering the bar F
which may be conveniently effected by making centre of the link adjustable
upon the carrier F.
As soon as one side of a blade is finished the propellor is raised up and turned
partially round on the shaft C2 and another blade placed on the table C. After all
the blades have been thus planed on one side the propellor is turned entirely over and
the operation repeated on the other sides of the blades, a suitable block C being
provided for this purpose.
It is evident that in order to procure exact correspondence between the blade and
the pattern the same part or point of the tracer should always remain in contact with
the pattern, otherwise if the point in contact changes the effect on the cutting tool
will be the same as if the tracer had been altered in length and an unforeseen altera-
tion of this sort would militate against the accuracy of the work and as the pressure
upon the tracer is severe it is important that the material about the end in contact
with the pattern should be arranged to resist the strain to which it is subjected;
a pointed end is obviously unfit for the purpose and if the end be rounded off the
point of contact must necessarily change in passing over surfaces of varying curvature.
The form of tracer I prefer to use is shown in elevation in figure 4, in plan in
figure 5 and in vertical section in figure 6. G is a cylindrical chuck with a taper
shank G which fits into a recess in the end of the tracer bar F.
A plug G2 having also a taper shank is fitted concentrically into the chuck the
annular space between the plug and the inner wall of the chuck being occupied by
parallel ribs of metal G³ which fit somewhat loosely so that when the tracer is vertical
the ribs if not prevented will fall out of the cylinder G. In the end of the plug G² is
a cavity within which rests the half of a sphere G the flat side thereof bearing against
the surface of the block C. As the tracer travels over the convex surface of the latter
the half sphere G rocks in its seat whenever the angle of curvature changes but as
the actual point of resistance must be situated at the centre g of the sphere and as
the distance of this point g from any other point situated in the vertical axis of the
holder must necessarily be constant, the length of the tracer is unaffected by the
rocking of the sphere and the variations in the surface of the block C are transmitted

page_text: analtered to the cutting tool f. Owing to the shallowness of the cavity in the
plug G and to the resistance encountered by the hemisphere G the latter is liable to
become displaced especially when travelling over a surface which is strongly inclined
as shown in the drawing. In this case the ribs G³ come into action rising and falling
with each change of surface and always encircling the hemisphere and pressing upon
the same at points lying in the same plane as the centre or point of contact g.
The machine is driven as follows:-
H is the first motion shaft on which are the usual driving and reversing and loose
pulleys H1, H2, H3. The portion of the shaft between the bearings h, h is threaded
and passes through nuts on the underside of the carriage E to which it imparts the
necessary cutting and return strokes, the cuts in this instance though not necessarily
always being across the blade of the propellor. The reversal of the carriage and the
feed motion of the tool carrier may be effected by any of the ordinary well known
methods usually adopted in planing or shaping machines.
The shaft B connecting the tables B and B is controlled by means of a capstan-
wheel L on the axis of which is a pinion L gearing with a toothed wheel L² mounted
on the end of a shaft L3 which is supported in bearings formed on the frame A. On
the shaft L³ is a worm L which gears with a toothed segment L' fixed to the shaft B.
By turning the capstan wheel I any desired inclination can be imparted to the
beds B and B and the person in charge of the machine can vary the position or
angle of the blade and the pattern.
Where practicable I prefer to cause the tool to travel across the blade arranging
the tables B and B and their operating mechanism as already described and shown
in the drawings; but when it is necessary the blades may be machined in the direction
of their length the tables B1 and B2 being rotated upon axes parallel with the length of
the blade, the axes of motion, of the tables in that case being parallel instead of
coincident.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed, I declare that what I claiin is:
--
1. The manufacture of screw propellor blades by shaping and finishing the surfaces
by means of a tool whose motion or path is automatically adapted to the varying
surface of the blade substantially as herein described.
2. The use in machinery such as is herein referred to of the means described for
keeping the varying face of the pattern and of the object operated upon in a suitable
position for the tracer and the tool to traverse by partially and simultaneously
revolving both the pattern and the object operated upon substantially as described and
illustrated in the accompanying drawings.
3. In machinery such as described the method of maintaining unaltered the length
of the "tracer" by means of a movable hemisphere such as G the plane of whose
contact face is alterable without varying the length of the "tracer substantially
as described and illustrated in the accompanying drawings.
4. In machinery such as described and as a means of maintaining unaltered the
length of the tracer the combination with the plug G² of a hemisphere such as G*
adapted to move in a recess in the end of G and ribs such as G³ the whole constructed
and operating substantially as and for the purpose described and illustrated in the
accompanying drawings.
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