Improvements in Rotary Cutters for Metal.
Year: 1890

page_text: Date of Application, 24th Sept., 1890
Complete Specification Left, 15th June, 1891-Accepted 18th July, 1891
PROVISIONAL SPECIFICATION.
Improvements in Rotary Cutters for Metal.
We, BENJAMIN CHEW TILGHMAN and GEORGE RICHARDS, both of Atlantic
Works, Broadheath, Cheshire, Engineers, do hereby declare the nature of this
invention to be as follows:-
Our invention relates to that class of rotary tools for cutting metal which has
removable blades and it particularly refers to an improved method of fastening
such blades into the central block or body of the tool. The usual method of
fastening such removable blades has been by set screws, but this is not well
adapted for cutters of small diameter or for blades having a considerable length
of cutting edge.
Our invention consists in making a series of narrow radial slits in the circum-
ference of the central block, and inserting the cutting blades into these slits, but
leaving vacant slits at intervals, and then driving into these vacant slits wedges or
conical pins so as to open or widen them and thus bring a sideway pressure on the
adjacent slits and cause them to close together and bind fast the blades they
contain. Provision is made for driving out the wedges or cones and thus relieving
the elastic pressure on the adjacent blades which can then be readjusted or replaced.
The radial depth of the slits, the thickness of metal left between them, the looseness
of fit of the blades in them and the proportion of wedge slits to blade slits, should
be regulated so that the sideway pressure of the wedges or cones will bind fast the
blades without exceeding the elastic limit of the metal.
Another feature of the invention is the use of cutting blades much thinner than
usual so that they can be made into spiral cutters.
The slit being cut to the
proper spiral, the flexibility of the thin blade allows it to bend and twist so as to
adapt itself to the curve and yet be solidly supported and fastened.
Also with thin blades a greater number of cutting edges can be obtained in a given
diameter, and the blades can be sharpened in place by an emery wheel so as to
grind away their whole thickness and thus retain the proper angle of clearance or
backing off of the metal behind the edge.
The invention can be applied to rotary cutters or milling tools of a great variety
of shapes, such as parallel, spiral, cylindrical, conical, angle or bevel mills, face
mills, gear cutters &c.
The blades can be made to cut at the ends as well as the sides. The term radial
applied to the slits is only approximate; generally they are inclined forward in
the direction of the rotation.
B. C TILGHMAN.
GEO. RICHARDS.
COMPLETE SPECIFICATION.
Improvements in Rotary Cutters for Metal.
We, BENJAMIN CHEW TILGHMAN and GEORGE RICHARDS, both of Atlantic
Works, Broadheath, Cheshire, Engineers, 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:-
Our invention relates to that class of rotary tools for cutting metal which has
removable blades, and it particularly refers to an improved method of fastening
such blades into the central block or body of the tool. The usual way of making
01

page_text: such tools has been to place each blade in a rigid socket, and fit and fasten it
individually by wedges or set screws, but this plan is expensive, and is not well
adapted for cutters of small diameter or for blades having considerable length of
cutting edge.
Our invention consists in making the sockets which are to hold the blades,
elastic and compressible, and in applying sideway pressure, so as to make the sides
of the socket grip the blades and hold them fast.
Referring to the drawing-
Fig. (1) is an end view and Fig. (2) is a vertical section of a cylindrical milling
cutter made according to our invention.
Fig. (3) is an end view, and Fig. (4) a vertical section of a bevel milling cutter.
Fig. (5) is an end view, and Fig. (6) a vertical section of a face mill.
Fig. (7) is a vertical section of a cutter having its central block made in one
piece with the stem.
The same numbers refer to like parts in each figure.
(1) is the central block or body of the tool, made preferably of mild steel.
(2. 2. 2) are slits made nearly radially round the circumference of (1), and along
its whole length; these slits are intended to receive the cutting blades (6. 6) and
will be called "blade slits." (3. 3. 3) are slits placed at intervals among the blade
slits, and parallel thereto, and are to receive conical pins (4. 4. 4) or wedges, and
be expanded thereby, so as to give a sideway pressure to the adjacent blade slits,
and make them grip the blades they contain. They are made deeper radially than
the blade slits, and will be called "wedge slits." We prefer to place the blade
slits in groups of about four, and then one wedge slit, but we do not confine our-
selves thereto. The blades are rectangular bars of thin steel made by rolling or
other process, and cut to length, and are to be of as nearly uniform thickness as
can be conveniently obtained, and they should be loose enough to be adjustable in
the slits. When the blades are all placed, the conical pins (4. 4. 4) of hardened
steel are gradually and successively driven into the holes in the wedge slits until
the blades are gripped tight enough for use, and the tool is then ground and
sharpened by an emery wheel in the usual manner.
We have obtained good results by making the blades project beyond the central
block a distance equal to about double their thickness, and by making them enter
into the body of the block about three times as much as they project beyond it,
but we do not confine ourselves thereto. It will be understood that the slits are to
be of such depth radially, and such proximity to each other, that the metal left
between them will be elastic, and will yield to the sideway pressure given by
driving in the conical pins (4.4) and will spring back when the pressure is removed
by driving out the pins, so that the slits will then open, and the blades can be
re-adjusted or removed. In long cutters two conical pins (4. 4) are used in each
wedge slit, one at each end, and a recess (5) Fig. (2) is made in the middle of the
slit, so as to expose the small ends of the pins in order to drive them out.
In short cutters, one pin in each wedge slit is sufficient as shown at (4) Fig. (4)
and (6).
When the blades get worn too close to the circumference of the central block,
they can be set out and packed up. In consequence of the uniform elastic grip of
the whole length of blade given by the sideway pressure, much thinner blades can
be used than in the ordinary method of fastening, with the advantage that a greater
number of cutting edges can be put in a given diameter of cutter, and its efficiency
be thus increased. Also the blades can be ground in place, so as to remove the
whole thickness of metal, and thus preserve the proper angle of clearance or
backing off from the cutting edge. The slits and blades may be either parallel to
the axis of the central block, or at an angle thereto, so as to make "skew” cutters
as shown in Figs. (2. 4. 5 and 6).
of an
We find that steel bars can be rolled at moderate expense to about 10% or 1000
of an inch of a given thickness, but to bring them to say 2000 or
inch is very expensive. Parts of the same bar will differ perceptibly in
3000

page_text: thickness. Slits cut with the same saw will also vary in width. Our practice is to
cut the bars into pieces of the length of the blades, and to sort them according to
thickness as shown by a gauge, and then to fill each group of blade slits by making
the thick and thin blades compensate each other so that the group makes a nearly
solid mass, and requires but little sideway compression to be finally given by the
conical pins. The elastic grip peculiar to our method of construction allows a
solid tool to be thus built up out of parts which are only approximately accurate in
size, and can be cheaply made.
Our invention can be applied to rotary cutters, or milling tools of a great variety
of shapes, such as parallel, cylindrical, conical, angle or bevel mills, Figs. (3 and 4)
face or side mills, Figs. (5 & 6) gear cutters, etc.
The blades can be made to cut
at the ends as well as at the sides (Figs. 2 & 6). The term radial applied to
the slits is only approximate; generally they are inclined forward in the direction
of the motion. Usually milling cutters are made to fit on separate mandrels as
in Figs. (1. 3. and 5); this is convenient when they require to be annealed, and
re-hardened, but makes them liable to run out of centre. As the body of our
cutter is not hardened, we prefer to make it with a solid stem as in Fig. (7), but
we do not confine ourselves thereto. The thickness of the blades, and of the metal
left between the slits may be varied according to the kind of work to be done. For
light work on cast iron with a central block 34" diameter, we have put seven wedge
slits with four blade slits between each pair of them; the blades were about 1880 of
an inch thick, and were inserted into the block about of an inch, the wedge slits
going about of an inch into the block.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what
we claim is,
In rotary tools for cutting metal having several removable blades, the following
devices either singly or in combinations of two or more of them.
1.-Blades placed in slits made nearly radially in the circumference of the
central block, leaving between the slits enough metal to admit of being
temporarily and elastically bent sideways by pressure, so as to close together
the sides of the slits and grip the blades, and to open and loosen them when
the pressure is removed.
2. The combination at intervals among the blade slits of other slits which
receive conical pins or wedges, and are expanded thereby, so as to close the
adjacent blade slits, and make them grip the blades.
3.-
The combination of the blade slits in groups with a wedge slit on each
side of each group, so that the sideway pressure of the wedge will be trans-
mitted to several slits when containing blades.
4. The combination in the slits which receive the conical pins or wedges of
suitable recesses or openings, so that the pins can be conveniently
driven out.
5. The combination of blades thin enough to allow the whole width of the
cutting face to be ground away by an emery wheel, so as to retain the
proper angle of clearance with slits suitable to receive such blades.
All substantially as described.
Dated this 12th day of June 1891
B. C. TILGHMAN.
GEO.
RICHARDS.