IMPROVEMENTS RELATING TO GRINDING MILLS
Year: 1880

page_text: LETTERS PATENT to John Rae, of the City and County of New York, in the
State of New York, one of the United States of America, for an Invention of
"IMPROVEMENTS RELATING TO GRINDING MILLS."
PROVISIONAL SPECIFICATION left by the said John Rae at the Office of
the Commissioners of Patents on the 12th October 1880.
JOHN RAE, of the City and County of New York, in the State of New York,
one of the United States of America. "IMPROVEMENTS RELATING TO GRINDING
MILLS."
In carrying out my Invention I mount two circular plates or discs provided with
grinding surfaces on separate axes contiguous to each other, so that the back face
of the one and the front face of the other shall rub together.
The axes are not parallel to each other, but are so skewed that the opposed
surfaces at the lower portion thereof, or at a point a suitable distance from the top,
shall be very close together, while the upper portions are at an appreciable distance
apart.
The discs are conical, or rather conoidal, with their conical faces slightly hollowed,
and being revolved in different directions with their upper parts turning towards
each other, the motion of the opposed surfaces, by which I mean those parts of one
wheel which are overlapped by a portion of the other wheel, is downward.
By this form of surfaces and the obliquity of the axes I draw in the material
freely, and as the surfaces gradually close together, bring it between parts which
move across each other and properly guide it, and then properly discharge it.
My improved mill is capable of working material very rapidly, and delivering it
finely ground with little friction, and consequently with little heating.
The parts which I have termed discs may be made of any reasonable thickness,
and made of stone, or made of metal to enclose or confine stone. But however
made, and especially when, as in some of my experiments, made of metal alone, it
will be obvious that the small amount of heat generated in grinding will be rapidly

page_text: dissipated by the great surface presented, and, when metal, aided by its high
conducting power. The discs each move independently and uncovered with their
faces exposed both to radiation and to the cooling influence of the air which is
freely in contact therewith.
From all these causes the mill grinds cooler than any other known to me.
The Invention may be applied to great variety of materials of various physical
qualities. I esteem it most important for those materials which are injured by a
rise of temperature.
In constructing my apparatus I can employ a fixed framework and a light casing,
which, with the framework, forms a tight box which encloses all the dust which
might escape from the grinding. A fixed funnel or hopper supported by braces,
and of a thin or wedge form at its lower end, guides the grain or other material to
be ground into the narrow space presented between the two opposing surfaces of
the wheels or discs which effect the grinding.
One disc is mounted on a shaft which is horizontal, and stands squarely with the 1
frame. The other disc is mounted on a shaft which is oblique in both directions,
that is to say, it is inclined out of a horizontal, and it is also skewed or oblique
when seen in plan. The axes of the two discs are at a distance apart, only a little
greater than the semi-diameters of the corresponding discs. The discs are presented
with a portion of the face of each covered or presented against a corresponding 2
portion of the face of the other.
The grinding operation is all effected in the portion overlapping. The surfaces
are in contact or nearly so at the bottom, and are sufficiently wide apart at the top
to receive the material which is to be ground.
The material received through the hopper or otherwise into the wide apart 2
portion of the space between the discs at the top is drawn down, crushed, ground,
and delivered below in a finely disintegrated state, with a rapidity dependent on
the velocity of the discs, but which, by the construction of the mill, is intended to
be in all cases a very short period.
Collars may be employed to hold each shaft in a position approximating its true 3
position.
I prefer one shaft to be immovable endwise. It may be provided with a stout
set-screw pressing against each end.
The oblique shaft is provided with a set screw or other adjusting means held by
a bracket or bearing, a wedge operated by a screw, or other means may be 3
employed. The screw or bearing at the end operating against the shaft should be
slightly spherical to prevent too great friction, and allow of free movement and
regulate the fineness or coarseness of the ground material.
The other end of the oblique shaft is equipped with means, which are not only
adjustable, but also elastic, to allow the shaft with its disc to move in the direction 4
to increase the distance between the discs.
A plate bears against the end of the oblique shaft, and is provided with a hole
near each end receiving a bolt. Each bolt presses either directly or through a
suitable washer against a spring, which in turn bears against the plate.
In adjusting the mill for use, these bolts are set up so as to press the springs 4
with considerable force against the plate, consequently pressing the latter against
the end of the oblique shaft.
The bearings of the oblique shaft by preference are not collared, but are
cylindrical and capable of yielding when any too hard substance or too great
quantity of material is received from the hopper between the grinding surfaces.
In some cases I can drive both shafts by an independent belt, or I can drive
both by a single belt.
Tightening pulleys may be employed.
The faces of the discs I prefer to be slightly hollowed, they may however be

page_text: The faces of the discs may be formed with burr stone or other suitable material.
The ground material may be conducted away by any suitable means.
Air may be introduced through the shafts or otherwise to promote ventilation
and coolness.
In place of mounting the oblique shafts skewed in both directions, they may
both lie in the same horizontal plane, in which case the discs would approach
nearest to each other at the middle of the opposed or over lapping portions, instead
of at the bottom. Or they may lie so that they appear parallel in plan view, the
obliquity being all in the inclination from the horizontal, or only seen in the end-
view. Adjustable boxes may be employed to vary the obliquity..

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Rae in the Great Seal Patent Office on the 30th March 1881.
JOHN RAE, of the City and County of New York, in the State of New York,
one of the United States of America. "IMPROVEMENTS RELATING TO GRINDING
MILLS."
In carrying out my Invention I mount two circular plates or discs provided with
grinding surfaces on separate axes contiguous to each other, so that the back face
of the one and the front face of the other shall rub together.
The axes are not parallel to each other, but are so skewed that the opposed
surfaces at the lower portion thereof or at a point a suitable distance from the top
shall be very close together, while the upper portions are at an appreciable distance
apart.
The dises are conical, or rather conoidal, with their conical faces slightly
hollowed, and being revolved in different directions, with their upper parts turning
towards each other, the motion of the opposed surfaces, by which I mean those
parts of one wheel which are overlapped by a portion of the other wheel, is
downward.
By this form of surfaces and the obliquity of the axes I draw in the material
freely, and as the surfaces gradually close together bring it between parts which
move across each other and properly guide it, and then properly discharge it.
My improved mill is capable of working material very rapidly, and delivering it
finely ground with little friction, and consequently with little heating.
The parts which I have termed discs may be made of any reasonable thickness,
and made of stone or made of metal to enclose or confine stone. But however
made, and especially when, as in some of my experiments, made of metal alone, it
will be obvious that the small amount of heat generated in grinding will be rapidly
dissipated by the great surface presented, and, when metal, aided by its high con-
ducting power. The discs each move independently and uncovered, with their
faces exposed both to radiation and to the cooling influence of the air, which is
freely in contact therewith.
From all these causes the mill grinds cooler than any other known to me.
The Invention may be applied to a great variety of materials of various physical
qualities. I esteem it most important for those materials which are injured by a
rise of temperature.
In constructing my apparatus I can employ a fixed framework and a light casing,
which with the framwork forms a tight box which encloses all the dust which might
escape from the grinding. A fixed funnel or hopper supported by braces, and of a
thin or wedge form at its lower end, guides the grain or other material to be
ground into the narrow space presented between the two opposing surfaces of the
wheels or discs which effect the grinding.
One disc is mounted on a shaft which is horizontal, and stands squarely with the
frame. The other disc is mounted on a shaft which is oblique in both directions;
that is to say, it is inclined out of a horizontal, and it is also skewed or oblique
when seen in plan. The axis of the two discs are at a distance apart only a little
greater than the semi-diameters of the corresponding discs. The discs are presented
with a portion of the face of each covered, or presented against a corresponding
portion of the face of the other.
The grinding operation is all effected in the portion overlapping. The surfaces
are in contact, or nearly so, at the bottom, and are sufficiently wide apart at the top
to receive the material which is to be ground.

page_text: The material received through a hopper or otherwise into the wide apart portion
of the space between the discs at the top is drawn down, crushed, ground, and
delivered in a finely disintegrated state with a rapidity dependent on the velocity
of the discs, but which by the construction of the mill is intended to be in all cases
a very short period.
Collars may be employed to hold each shaft in a position approximately its true
position.
I prefer one shaft to be immovable endwise. It may be provided with a stout
set screw pressing against each end.
The oblique shaft is provided with a set screw or other adjusting means held by
a bracket, or bearing, or wedge operated by a screw, or other means may be
employed.
-
The screw or bearing at the end operating against the shaft should be slightly
spherical to prevent too great friction and allow of free movement, and regulate
the fineness or coarseness of the ground material.
The other end of the shaft is equipped with means which are not only adjustable,
but also elastic, to allow the shaft with its disc to move in the direction to increase
the distance between the disos.
A plate bears against the end of the oblique shaft, and is provided with a hole
near each end receiving a bolt. Each bolt presses either directly or through a
suitable washer against a spring which in turn bears against the plate.
In adjusting the plates for use these bolts are set up so as to press the springs
with considerable force against the plate, and consequently pressing the latter
against the end of the oblique shaft.
The bearings of the oblique shaft by preference are not collared but are cylin-
drical, and capable of yielding when any too hard substance or too great a quantity
of material is received from the hopper between the grinding surfaces.
In some cases I can drive both shafts by an independent belt, or I can drive both
by a single belt.
Tightening pulleys may be employed.
The faces of the discs I prefer to be slightly hollowed; they may however be
plane.
The material may be supplied by any suitable means in place of a hopper.
The faces of the discs may be formed with burr stone or other suitable
material.
The ground material may be conducted away by any suitable means.
Air may be introduced through the shafts or otherwise to promote ventillation
and coolness.
In place of mounting the oblique shafts skewed in both directions they may both
lie in the same horizontal plane, in which case the discs would approach nearest
to each other at the middle of the opposed or overlapping portions instead of at
the bottom.
Or they may lie so that they appear parallel in plan view, the obliquity being
all in the inclination from the horizontal or only seen in the end view.
Adjustable boxes may be employed to vary the obliquity.
But that my Invention may be fully understood I will proceed to describe the
same more in detail by the aid of the accompanying Drawings, which form part
of this Specification, and represent what I consider the best means of carrying out
the Invention.

page_text: Figure 3 shows one of the shafts and the collars by which it is held against
end motion.
Figure 4 is a section through a part of one of the discs.
Figure 5 is a section through a corresponding part of the opposite disc.
Figure 6 is a diagram showing the relative positions of the grinding discs when
seen in Hide elevation.
Figure 7 is a diagram showing the same in edge view with the inclination
exaggerated.
Similar letters of reference indicate corresponding parts in all the Figures.
A is the fixed framework, and A¹ a light casing, which, with the framework A,
makes a tight box which encloses all the dust which might escape from the
grinding; A is a fixed funnel or hopper, supported by braces A, A³, and of a thin
or wedge form at its lower end, adapted to guide the grain or other article to be
ground into the narrow space presented between the two opposing surfaces of the
wheels or discs which effect the grinding.
The disc B is mounted on a shaft b, which is horizontal and stands squarely with
the frame. The disc C is mounted on a shaft c, which is oblique in both directions,
that is to say, it is inclined out of a horizontal, and it is also skewed or oblique
when seen in plan. The axes b, c, are at a distance apart only a little greater than
the semi-diameters of the corresponding discs B, C. The discs are presented with
a portion of the face of each covered or presented against a corresponding portion
of the face of the other. The grinding operation is all effected in the portion
marked B¹, C', in the diagram, Fig. 6. The surfaces are in contact, or nearly so, at
the bottom, and are sufficiently wide apart at the top to receive the material which
is to be ground. The material received through the hopper or otherwise into the
wide apart portion of this space B¹, C', at the top is drawn down, crushed, ground,
and delivered below in a finely disintegrated state with a rapidity dependent on
the velocity with which the discs are rotated, but which by the construction of
the mill is intended to be in all cases a very short period.
The shaft 6 is intended to be immovable end wise. It may be provided with a
stout set screw, not represented, pressing against each end in the manner shown at
the pulley end of the shaft c.
The shaft c has a set screw D tapped through a stout bracket A*, which forms a
part of the fixed framework. The screw bears against the end of the shaft c. Its
bearing end should be slightly spherical, and the jam-nut, not represented, set
tightly against the bracket A, may aid in holding the screw very solidly in any
position in which it is adjusted. This prevents the disc C from moving too closely
against the diso B when the mill runs empty.
с
The other end of the shaft c is equipped with means which are not only adjustable
but also elastic. It allows the shaft c, with its disc C, to move in the direction to
increase the distance from B..
G is a plate which bears against the end of the shaft c, and is formed with a
hole near each end receiving a bolt H. Each bolt H presses either directly or
through a suitable washer against a thick spring I, which in turn bears against the
plate G. In adjusting the mill for use the bolts H are set up so as to press the
spring I with considerable force against the plate G, and consequently to press the
latter against the end of the shaft a
It being understood that the bearings of the shaft o are not collared, but are
cylindrical, the yielding when any too hard substance or too great quantity of
material is received from the hopper between the grinding surfaces will be readily
understood.
I can drive both shafts b, c, by an independent belt from a counter-shaft, not
shown, or I can drive both from a single balt running properly in contact with
the driving palley on each shaft. J is a tightening pulley, which may be set up
and down within considerable limits, and serves when the parts are thus driven

page_text: not only to maintain the belt at the proper tightness, but, by causing the belt to
hug around a greater portion of the periphery of the pulley on B, promotes the
conveyance of a proper quantity of power to that shaft. Ordinarily the shafts b, c,
will be geared together in addition to a proper arrangement of the belts to drive
them.
I think the surfaces of the discs which are presented towards each other tend
to become slightly hollow by use, that is to say, the discs are thicker in the
middle than at the periphery, but the surfaces instead of being true cones are
conoids, the line from the centre to the periphery being slightly curved inward.
I propose to make them so in the first instance, if desired. In Figs. 4 and 5 the
faces are intended to be thus alightly hollowed.
Modifications may be made. The hopper may be dispensed with, and the
material supplied by other means. Agitators, force, feed, or other devices may be
employed for supplying the material to be ground.
The faces of the discs may be formed with burr stone or other ordinary or
suitable refractory material secured in any reliable way in or upon the wheels,
which I have termed discs. The ground material may be conducted away con-
tinuously through a spout or other ordinary or suitable means. I have shown
simply a box K to form a receiver for the ground matter. Air may be introduced
through the centres of the shafts or otherwise, to promote ventillation and
coolness.
Obviously the bearings may be widened and protected by stuffing boxes, leather,
or other means, against the entrance of grit in grinding earthy matter.
Instead of mounting the skewed shafts o skewed in both directions, they may
both lie in the same horizontal plane, in which case the discs would approach
nearest to each other at the middle of the opposed or overlappping portions instead
of at the bottom. Or they may lie so that they appear parallel in plan view, the
obliquity being all in the inclination from the horizontal, or only seen in the end
view. I have experimented successfully in the shafts mounted in this latter
position. I propose to employ adjustable boxes with set screws to vary the
obliquity.
The tendency of my mill is to wear the surfaces with a very close approach to
uniformity. The centre of each stone or wheel within the line of rubbing should
be sunk out of contact.
Having thus described my Invention, I would have it understood that I do not
confine myself to the exact details as shown and described, so long as the peculiar
characteristics of my Invention be retained substantially as described, but what I
do claim is,-
First. In grinding milla, in combination with suitable means for supplying and
receiving the material, the dises or wheels B, C, turning towards each other and
mounted in skewed positions so that the upper portion of the adjacent surfaces B¹, C¹,
shall be wider apart than the lower portion, with provisions for adjusting the
distances at will, substantially as herein specified.
Second. In combination with the discs B, C, turning towards each other and
mounted in skewed positions, as shown, the yielding bearing G, held to its work
by one or more springs I, with adjusting means H, adapted to allow the separation
of the discs in emergencies, as herein specified.
Third. The combination of the hopper A*, formed so as to extend down a little
between the surfaces B, C, in combination with the wheela B, C, mounted on axes
which are out of parallel, all adapted to operate substantially as and for the purposes
herein set forth.
Fourth. The grinding mill described, having the discs B, C, with slightly hollow
conoidal faces arranged as described, in combination with the hopper A', adjusting
means D, G, H, and yielding springs I, as herein specified.

page_text: Fifth. The hollowed discs or wheels B, C, constructed and adapted to operate
substantially as described.
-
In witness whereof, I, the said John Rae, have hereunto set my hand and
seal, this Twenty-fourth day of November, in the year of our Lord One
thousand eight hundred and eighty.
Witnesses,
WILLIAM COLBORNE BROOKES.
THOMAS DREW STETSON,
Patent Solicitor,
23, Murray Street,
New York.
JOHN RAE (LS)