IMPROVEMENTS IN GRINDING MILLS
Year: 1885

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I ALFRED JULIUS BOULT of 323 High Holborn in the county of Middlesex,
Engineer do hereby declare the nature of this invention for "IMPROVEMENTS IN
GRINDING MILLS a communication from Johann Christoff Ludwig Pestrup, and
Gerhard Diers, both of Gröpelingen, near Bremen, German Empire and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
The hereinafter described improvements relate to mills more particularly those
adapted for agricultural purposes. In accordance with this invention the rotation
of the one stone is transmitted to the other and the two stones are dressed with
furrows which are of parallel trapezoid shape or circular shape in transverse
section thereby enabling the stones to be used in either direction of rotation.
In such a mill both stones will therefore be runners and as a rule they will be
driven in opposite directions though they may rotate in the same direction but at
different velocities if desired say where the grist is to travel in a given direction.
Either form of rotation is best transmitted by means of belts ropes or the like
which either run on the stones themselves or on pulleys and are led over guide
rolls, the latter are mounted in adjustable bearings so as to allow the belts or ropes
to be tightened. In some cases, it may however be more desirable to use toothed
gearing for transmission.
The accompanying drawings show the arrangement of vertical as well as of
horizontal stones, whilst diagrams indicate various ways of transmitting motion
from one stone to the other.
In Figures 1 1ª and 1b is shown a mill with vertically rotating stones in which
an endless belt c passes directly over both stones and is secured in its position by
two guide rolls AA whose forked bearings a a are suspended by screw bolts bb
from the framing E E of the mill.
The left hand side of Figure 1 also shows the dress of the stones by means of
radial furrows between which may be provided a greater or less number of radial
or other furrows.
Both stones R¹ R' are supported on separate independent axles D¹ D' each
carried in a pair of bearings d d which in turn are carried by castings which reach

page_text: into the eye of each stone and are rigidly connected with the framing E E. On
the shaft D¹ of the stone R¹ there is fixed either a pair of pulleys CC (say one
fixed and one loose) for driving the mill by suitable power or a crank is fixed
thereon for driving by hand.
Over the other shaft D', driven by the endless belt e a hopper G is fixed on the
casing K which terminates near to and above the box like connecting piece of the
bearings. The hopper discharges its contents upon a wooden block which is square
in cross section and rotated by the axle D
"
This quadrangular wood block prevents overcharging of the box like connecting
piece of the bearings and in some measure serves instead of a horizontal screw
conveyer for moving the grist on the slightly inclined bottom of the said connecting
piece and towards the space between the stones. The radial shape of the furrows
which traverse the stones notwithstanding the grist can not fall through between
the stones and into the chute or spout F until it has attained the requisite degree
of fineness as the great velocity of the stones prevents premature discharge
whilst the grinding is also more thorough than is possible with the customary
arrangements.
To enable the distance of the two stones R¹ R³ from one another to be regulated
shaft D is capable of adjustment in its bearing by means of the screw e passing
through the piece & projecting from the bearing. This casting d¹ may be replaced
by an ordinary bridge piece.
In the mill with horizontal stones shown in Figures 6 and 6ª the movement of
one stone R to the other R¹ is effected in the same manner as with the above
mentioned vertical mill.
The whole space containing the stones is surrounded with a casing c of sheet
metal fixed on the mill framing; the casing may be of wood or the like if preferred.
Upon said casing the box like housings for the tightening or leading rolls are
provided and the latter afford a bearing for the adjusting screws bb to work in.
Into the, preferably wooden, top of casing e a hopper G is inserted and the
hopper is by preference fitted with a guiding partition as shown dotted in Figure 6
and in full lines in Figure 6a. Into the wooden bottom of the chamber enclosed
by the above named casing e, the chute or spout F is inserted and serves to conduct
the ground material away.
A peculiar feature of this mill is the way in which the shafts K and h of the
stones are mounted of which the former is driven directly the latter being rotated
indirectly by transmission of motion thereto through the belt l.
The former shaft K reposes on a pointed journal resting in a footstep H firmly
connected with the bed of the mill. The other shaft h is inserted into the hollow
interior of the first shaft and its pointed lower end bears upon a cross piece i
passing through a slot in the outer shaft and carried by a nut thereon. This
means ensures not only freedom of motion of the two shafts which run in
collars d¹ d³ but also allows the shaft h to be easily raised or lowered so that the
distance between the stones can easily be adjusted.
In mills of large size it may not be convenient to run the belts round the
stones R R¹ themselves, and in that case they pass round pulleys C° Cº1 (see
Figures 4 and 4a) fixed on the outside of the stones and concentrically therewith.
With such an arrangement not only is less strain put upon the belts but by
taking pulleys of different size different speeds may be imparted to the stones.
If much power has to be transmitted from one stone to the other so that the
strain upon the belts is considerable, it will be advisable to journal the guide
rolls A A in such a manner as to reduce frictional resistance as much as possible.
To this end they may have their journals running in grooves of the double disc B
(Figures 2 and 2) the latter being in such case provided with the necessary
With this arrange-
adjusting devices (such as the bridge piece a and set screw b).
ment the rotation of A induces rotation of the double disc B also and the friction
of the journal diminishes in proportion to the relation of the exterior diameter of
disc B to the diameter of the journals of the same. For the same, purpose the

page_text: journals a of the guide rolls A may run on pairs of bearing rollers B¹ B° Figure 3
mounted on cross pieces fitted with set screws bb. The two axles a a of the guide
rolls may be united into one and this may freely rest on two pairs of bearing
rollers (Figure 3); in the latter case the roller over which the less stretched part
of the belt runs is loose on the shaft or the stretched part of the belt runs crossed
over the rollers and both are fixed on the shaft a. The latter mode is preferable
with an arrangement such as illustrated in Figures 4 and 4ª provided the distance
between the guide rolls and the pulleys is large enough.
Figures 5 and 5* show how the motion may be directly transmitted from one
stone to the other by toothed gear.
To this end the shaft of the directly driven stone may pass through both and
that to be driven off it viz the second stone may slip over the shaft and have an
internally toothed wheel. With this gears an intermediary pinion Z driven by
the toothed wheel Z¹ on the directly driven stone.
Having now particularly described and ascertained the nature of the said
invention 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). The method of employing two mill-stones which both rotate, one of these
being directly driven the other receiving power from the first either by belts ropes
or the like led over suitable pulleys, or by toothed gearing.
2). The arrangement for transmitting the motion by a belt, rope, or the like led
over two guide rolls A which either runs on the two stones R¹ R³ directly
(Figures 1-3 and 6 and 6º) or on pulleys fixed upon and concentrically with the
stones (Figures 4 and 4 with or without such bearings for the axles of the guide
rolls as shown in Figures 2 to 3* and serving to reduce the friction.
3). The employment of two stones both simultaneously rotating on horizontal
shafts.
4). The journalling of the vertical shaft h. of one stone in the shaft K of the
other (Figure 6 for which purpose the latter is made hollow and has a slot for the
purpose of receiving a plate i. which serves as a step bearing for the pointed end
of shaft h. the plate or cross piece i being supported by a nut J screwed upon the
shaft K.
5). The general arrangement and construction of the parts shown in Figures 1 to 6
of mills with vertically or horizontally rotating shafts.
6). The employment of a radial dress.