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The Roller Mill & Silo Manual


A Ready Reference Book
for the
Modern Miller & Millwright

Containing Rules, Tables and Information
Useful for Millers, Millwrights and those
concerned with Mill General Grinding
and Grain Storage and Transport Machinery

Fourth Edition
Printed by the Northern Publishing Company, Ltd., 17 Goree Plazzas,


About the year 1880, when Flour Mill Engineering and Flour Manufactured entered a new era, Millers and Engineers were under a great disadvantage, having no literature or publications in book form for reference purposes. Since that time engineering generally has made immense and rapid advances, and it soon became evident that improvements on old methods of grain transport, storage, cleaning and reduction of flour were possible and necessary.

The late James Donaldson in the year of 1885, issued the small book called "The Roller Mill Annual," containing 162 pages. This ultimately developed into the "Roller Mill Manual," published in 1890. A second edition revised and enlarged, was issued in 1901, and a third one, in which many additional illustrations and references were added, was published in 1912. The present edition, revised, brings the work up-to-date. We are indebted to Mr. Gerald Fitzgibbon for the article on "Oat Milling." In a manual of this size, it is impossible to treat fully the subjects referred to, as will be clear on reference in the Syllabus given on page 163.

The methods of manufacturing flour cannot be taught or learned from books, the only true, practical, and permanent place being the Mill, where, the sometimes complex and elaborate methods may be seen in full operation.

The Publishers.


ACTION. The action of a millstone is that of a tearing, cutting, or grinding nature without appreciable compression of the feed, unless overfed. At starting it is advisable to supply a large feed, and so allow the stones to be thoroughly filled up before commencing to set their usual work.

ADJUSTMENT GEAR. This usually consists of a lever or bridge tree, rods, hand wheel, etc., used for adjusting the runner stone, to regulate the fineness of the reduction of the feed by raising or lowering the spindle and the stone. With an under runner, the usual plan is to have the adjustment made by moving the upper fixed stone, by three or four screws at the periphery. The adjustment should be possible either on the stone floor, or below it, or both.

AUTOMATIC ALARM. This is an appliance situated in the feed hopper or its adjacent parts, to give some warning when the feed has cease to flow, or when the stones are running empty, as avoiding any injury to the millstones, or any chance of firing. One form adopted is that of a floating disc, upon which the feed falls, so retaining it in a certain position which, if varied by the cessation, cause an alarm bell to be sounded.

BACK. On an upper runner this is the top part, and consists of a thickness of plaster mixed with alum water, in which are bedded spalls or pieces of burr stones, the top surface being turned true and even, whereby the balancing is facilitated. In this back the balance boxes are embedded flush.

BACKLASH. It must be noticed that the moment of inertia of the Prime Mover must be exceed that of the machine driven, to avoid backlash. With gearing this work denotes the clearance between the teeth.

BALANCING. As the materials used in the construction of millstones are not uniformly distributed as regards weight, and as the stone is subject to gravitational and centrifugal forces acting at the same time when the stone is in motion, irregular, undulatory or wobbling motions occur, and the working face will not keep perfectly horizontal, then some adjustments must be made to obtain uniformity of action at all points of the face.

After attaining the standard balance, should be the part DW shown in Figure #1 rise when running, then the weight BW must be raised in the box, so that its downward action may be increased, until the upward tendency of DW is neutralized. To meet the influence of gravity, the standing, stationary, or static balance must be first made, afterwards the centrifugal force is provided for, whereby the running or dynamic balance is attained without any interference with the already made static balance. These corrections are obtained by a process of trial, error and correction, not always an easy performance.

BALANCE BOXES. Four or more iron boxes to hold adjustable weights are fixed near the outer periphery of the stone, in order to get the standing and running balance, that is to adjust the center of gravity so that it shall be directly over the point of support. In some cases there are two boxes, the outer one fixed in the stone, and the inner one, with center screw and weight fitting inside. Vertically adjustable weights affect the running balance without altering the standing balance. theoretically, the standing balance, is better obtained by adjustable weights placed in the horizontal plane passing through the center of gravity, that be a neutral position.

BALANCE RYYND. The cross bar to carry the running stone, and fixed to it. The working centers should be in the same horizontal plane as the point of support, or suspension on the spindle, as the case may be, to avoid an unnecessary torque or twist on the rhynd, as is possible with the arrangement shown in Figure #3 where, in case, the bearing points of the rhynd on the driver, as o and d, may not be always in contact at he same time, due to bad fitting or wear when these will be a twisting leverage equal to the distance a, b, and the stone consequently, will be thrown out of level.

BEHRN'S EXHAUST. This consisted of a dust strainer of long haired flannel stretched above the millstones, and was much in use.

CASTING HOOP or CURB. This is the cover, enclosing the millstones and supporting the feed mechanism; when an upper runner is used it is made of hard wood tongued and grooved joints, iron bands, all varnished on the outside and should never be painted on the inside. Sheet iron hoops are made for special work.

CENTER OF GRAVITY. This is a point where the whole weight of the material forming the millstone may be considered as concentrated, and is used for calculating forces, stability, and etc. Its position may be ascertained by calculation or by experiment, and is assumed to be at the vertical axis of the stone at the eye. In a doomed back stone it will not be at the geometrical center of the transverse section, but some distance below it. The position of "Center of Gravity" determines the point of support or suspension, which for a balanced runner stone, will be above "Center of Gravity." In a millstone there are three positions deserving consideration. (1) - If the point of support be below "Center of Gravity," the stone will be unstable and take up an incline position, and except at very high speeds will wobble. (2) - If the point of support coincides with the "Center of Gravity" the stone will be in an indifferent or in a neutral state of equilibrium, attaining a horizontal position when running, with the possibility of undulating. (3) - If the point of suspension be above the "Center of Gravity," as us usual, then there will be a reluctance to depart from a horizontal position whether at rest or running. See the first drawing.

French Burr weights about 160 pounds. per cubic foot, but the more honeycombed variety may weight from 90 to 120 pounds per cubic foot. In the backing of a built up millstone consisting of plaster, in which are placed pieces of burr stone - spawls - for binding the mass, the weight may be about 130 pounds per cubic foot, in which the plaster is assumed to weigh 100 pounds per cubic foot. This lighter weight of the backing lowers the position of the "Center of Gravity," as compared to what the position would be were the whole body of the stone of uniform weight and of burr stone.

CENTRIFUGAL FORCE (C). This will be equal to W x V2 divided by 32.3 x r, where W = weight in pounds, V - velocity in feet per second, r = radius of gyration. For a 4 foot millstone C = 7,900.

COCKHEAD. Upon this rests the rhynd. Figure #3 and 3a show two forms. See first drawing.

CONSTRUCTION. They are constructed of a great variety of stones, such as Derbyshire Peak, Newcastle Grit, Belgian dark marble, German Cullen stones, Porous lava, and etc., but the usual and most suitable stones are quarried at La Ferte sous Jonare in France.

Blocks of various sizes are used of those burrs to build up the stone, the joints being symmetrical, but differing for the runner and fixed stone. For stones grinding various vitrous materials the radiating joints are made to coincide as near as possible with the bottom line of the furrows, so preventing the breaking away of small angular pieces when in use. With Composition stones this need not be considered. The jointing material is of cement, lead, or plaster, and is good work the joints should be fine, even, and extend with the stone from the face towards the back for about 9 or 12 inches, for a runner stone.

Composition stones constructed of concrete, spalls, Portland cement, and etc., have special facing of emery, corundum or other material of a hard nature.

The better class of burrs are in small pieces. The individual stones for intensive work, should be built end on, that is with the grain square to the face.

Burr stones vary in hardness and porosity, the usual qualities are hard, soft, close or open, and of white, brown, violet and other shades of color. Small size millstones are made of one piece. For oats, the honeycomb variety is suitable. The stones at the bosom or breast are made of a harder quality than for the skirt for single purpose. If the millstones happen to be out of balance and touch, you would have hard stone touching hard stone. Rather than soft touching soft, or hard touching soft. This way hard stone touching hard stone would do less damage to the stones and to the dress on the millstones.

CRACKING. Lines of indentations on the lands, running parallel with the furrows. They are cut with a mill bill or diamond on a special tool for that purpose, and are spaced so that from 6 to 30 lines may be made per inch, according to the material to be treated.

CRANE. Where there is no overhead traveler, a crane is required for fixing or removing the millstones. If there is no possibility of using the guy stay, the jib must be of sufficient strength to carry the stone, and the top socket deep and well fixed. Square thread on the screw so the weight of the stone will not unscrew the thread downward. The whole made so as to be easily fixed or removed.

DIRECTION RUNNING. This is stated as, revolving with the sun, like the fingers (hands) of a watch; or against the sun.

DISCHARGE SPOUT or CHUTE. This is so constructed that an examination of the reduced material may be made at hand holes, either level with the millstones floor or below it.

DISENGAGING GEAR. For this purpose clutches, fast and loose pulleys are required, so that any pair of stones may be put in or out of action as required. Remember raise the millstone first to allow all water to empty out of the buckets of the water wheel so potential energy is not stored within the system so the raising of the disengaging gear will not release that energy, damaging the machinery or injuring or killing individuals.

DRAFT or DRIFT or LEAD. This is the amount of eccentricity of the furrows, and is the radius of a circle at the eye to which a tangent line is drawn to fix the position of the back edge of the furrow. The old rule was, one inch per foot diameter of stone for the master furrow. If the speed is increased, the draft may be less. Some authorities consider that draft is not of much importance, and that to the centrifugal action must be attributed the chief cause for the flow of the feed between the stones.

Increasing the draft will permit of shallower furrows. Increasing the draft results in a greater shearing action on the feed. It should be noted that, although the master furrow as sown in Figure #7, say has a draft of 4 inches, the successive furrows have drafts of about 6 3/4, 9 5/8, and 12 1/2 inches respectively, for a 4 foot stone with a ten quarter dress.

DRESS. Figure #6 of the first drawing. "A" shows a 9.4 quarter less for a four foot stone. "B" is a sickle dress, in which the interesting angles are 38 degrees, a particle "P" is shown in the furrows. "C" is a dress of 24 leading furrows, and 24 skirt furrows, half of the surface being land and half being furrows of 1 1/2 inches width.

There is no uniformity in the dress for millstones. The following examples demonstrates this:

WHEAT (SOFT). Open Burr 4 feet in diameter, 22/2; furrows 1 1/2 inches by 3/16 inches; bosom 11/16 inches deep to 6 inches from skirt, 4 inch draft furrows and lands equal.

WHEAT (HARD). Close Burr 4 feet in diameter, 22/2 furrows 2 inches by 3/16 inches; 3/16 inches deep, 2/3 furrows 1/3 land, 16 cracks per inch.

WHEAT. Burr 4 feet in diameter, 12-3; furrows 1 1/4 inches to 1 3/8 inches by 3/16 inches deep, draft 4 1/2 inches.

INDIAN CORN. Burr 4 feet in diameter, 12 to 14/4; furrows 1 1/2 inches by 5/8 inches, 3 1/2 to 4 1/2 inch draft.

BARLEY. Peak stones, 12 to 14/3; furrows 3/8 inches deep, draft 4 to 4 1/2 inches, 10 cracks per inch.

OATS. Peak stone, close grain, no dress.

HOG MEAL. Burr 4 feet 2 inches in diameter, furrows 2 1/4 inches by 1/2 inch. 2 inch lands, draft 3 1/2 inches, 8 cracks per inch for 6 inches from skirt.

MIDDLINGS. Burr 4 feet in diameter, 14/3; furrows 1 3/8 inches by 3/15 inches deep at eye to 3/32 at skirt, draft 4 inches.

MIDDLINGS. Burr 4 feet in diameter, 14/3; furrows 1 1/2 inches by 1/4 inches, 2 inch lands, draft 3 1/2 inches, 10 cracks per inch on 8 inch face.

MIDDLINGS. Burr 4 feet in diameter, 23/3; 6/10 furrow, 4/10 lead.

MIDDLINGS. Burr 3 feet in diameter, 12/3; furrows 1 1/8 inches, 16 to 18 cracks per inch.

BUCKWHEAT. Open or closed Burr 4 feet in diameter, 22/2; furrows 1 1/2 inches by 3/16 inches; bosom 11/16 inches deep to 6 inches from skirt, 4 inch draft furrows and lands equal, 16 to 18 cracks per inch.

RYE and RYE MEAL. Open Burr 4 feet in diameter, 22/2; furrows 1 1/2 inches by 3/16 inches; bosom 11/16 inches deep to 6 inches from skirt, 4 inch draft furrows and lands equal..

DRIVER. A cast steel block fitted and keyed on the top end of the spindle, into this the rhynd or bail is fitted. It also may be forged and formed by a blacksmith but not welded together out of smaller pieces.

DRIVING. These are several methods adopted for transmitting motion and power from the line shaft to the millstone spindle. Spur wheels, beveled wheels, pulleys and belts, friction wheels, and direct action motors. Gearing may be noisy, the teeth of mortise wheels rapidly wear if out of alignment or when not lubricated, and they may require complete renewing because of neighbor worn teeth. Belts and ropes run smoothly. The pulley on the spindle should be as large as possible to prevent slip of the belt, it should be well crowned to retain the belt in the center of the pulley. The spindle neck and toe bearings should be extra long on amount of the transverse pull of the belt. The belt running horizontally will be wider than for a vertical position for the same power, and from 2 to 3 per cent more must be allowed for slip. The larger horizontal pulley may require a lip to keep the leather belt from slipping off. A pulley covered with leather or canvas will transmit 20 25 per cent more power than one not so covered. With a quarter twist drive the distance apart of the driver and driven pulleys should be not less than three times or more than four times of the diameter of the larger pulley, in order to avoid the use of riggers or jockey pulleys. For stones of the following dimensions the sizes here given for pulleys, etc., serve as a guide.

Diameter of Stones.........2 ft 6 in...3 ft 0 in...3 ft 6 in...4 ft 0 in....4 ft 6 in.
Diameter of Pulley...........1 ft 8 in...2 ft 2 in...2 ft 4 in...2 ft 8 in....3 ft 0 in.
Width of Pulley..................0..7.....0..8 1/2..0..10 1/2....1..0.....1..2.

DUTY. Millstones are used for reducing materials. Since 1890 Chilled Iron Rollers have been generally adopted for reducing wheat, etc., but many substances continue to be treated by stones, disintegrators, etc.

EYE. The opening at the center where the feed enters. A large eye needs less swallow. Sometimes the eye is made larger in diameter at the face than at the back to assist the flow of the feed. With high velocities, the feed may adhere to the eye surface, due to centrifugal action, which may be avoided by fixing a sleeve or conical metal bonnet to direct the feed downwards.

FURROWS. These are the grooves or channels cut in the face of the stones. The master furrows begin at the eye, or thereabouts, and extend to the verge. The tributary or branch furrows are those placed at an angle with the master furrows. The purpose of the furrows is that granulation, ventilation, distribution and conveyance of the feed towards the verge. The more numerous the furrows the greater will be the quantity passed between the stones. Each furrow consists of a back edge, the cheek, the slope and the feather or cutting edge. The usual forms of section are shown in the second drawing, and the one found most efficient, is the form number 1. The depths and widths vary considerable, according to the nature of the material to be reduced. Deep furrows work cooler than those that are shallow. Some times the branch furrows are cut into the master furrow to ensure cooler and quicker work. When small transverse furrows are cut into the master furrows, the centrifugal action is somewhat resisted. The surface of the furrows should be even and smooth, for an uneven furrow does irregular work. A bend or elbow in a furrow extending a few inches from the skirt will accelerate the rate of discharge of the feed as it becomes finer. But furrows are not always necessary, for surfaces merely cracked or nicked may suffice for reducing some fine materials. Complicated forms of dress, such as the Sickle and the Hyperbolic Spiral, are difficult to make and expensive to keep in order. For cement grinding only master furrows are made, the remaining being land roughened, see the second drawing. The face parts not furrowed are termed lands.

GYRATION. Taking the section of a runner stone as being approximately a rectangle, there is a horizontal circle where the whole of the material forming the stone may be considered as concentrated. Thus for a 4.0 millstone with a 10 inch eye, R=1.415 feet or 17 inches, and at 120 revolutions per minute the angular velocity at this radius will be 1,080 feet per minute, or 18 feet per second.

HOOPS or BANDS. Neglecting the adhesion of the cement at the stone joints, the metal bands at the circumference for binding the stones must be made to exceed the centrifugal force by a factor of safety of over 15. There are usually three hoops 1 1/8 by 3/8 thick, placed about 1 1/2 to 1 3/4 apart, also another small band near the face, about 5/78 by 1/4. Sometimes a band with vanes or wipers is used for ventilation the space between the stone and the casting, and for directing the materials ground to the discharge spout. The hoop joints should be dovetailed and welded, then heated and shrunk on the stone.

JACK STICK. A tool used for adjusting the bed stone for level and the spindle for a vertical position.

In the eye of the bed stone is fitted an iron box, in which are fitted three or more adjustable bronze, gunmetal, wood, or white metal pieces, upon which the spindle revolves, so forming the neck bearing, and is so placed that it may be as near as possible to the point, where the resistance of the running stone can be best received. The bearing must be made as dust proof as is possible. With an upper running and overhead drive, the neck bearing will be replaced by a small toe step bearing sufficient to keep the stone and spindle in position.

PATH OF TRAVEL. Once the feed enters between the stones its path during the process of reduction is not radial, but more or less a spiral one, for an upper runner stone. Much depends upon the type of dress, the speed, and the material being ground.

POWER. Once actual horse power is required to reduce one bushel of wheat per hour on a 4.0 stone, but the power will increase with additional feed and pressure.

RUNNER STONE. This may be either the under or upper stone, or both. With an under runner stone there is no accumulation of the feed at the eye and the upper stone is adjusted easier.

When the upper stone is the runner there is a certain amount of buoyancy when the feed is between the stones, so reducing the weight on the top step to the extent of 60 to 70 per cent, and possibly with an excessive feed the spindle with the attached gear may be the only weight upon the toe.

There is an old saying that the weight on the toe is lessened by one hundred weight for each bushel of corn (wheat) ground per hour. For reducing vitreous materials, with an upper runner the overhead drive is preferable, as shown in figure number 5. "A" is a spindle for adjusting of the runner.

SAUCER. This is a metal disc, plain or dished, revolving with the spindle upon which the feed falls, and is distributed in a spray towards the swallow.

SHAKING SHOE. This consists of a small box placed at an angle, into which the feed is supplied and is supported on a flexible rod, and etc. By the use of a damsel attached to the spindle the shoe is made to shake, and so keep the feed flowing inot the eye. This is now dispensed with, and what is termed a silent feed tube used in its place.

SPINDLE. The central steel revolving axle by which motion and power are received for driving the millstone. The parts are, the toe, body, neck, driver seat, and cockhead. They are made from 6 to 11 feet long and the diameter vary from 3 1/2 to 4 1/2 inches, and must be free from any transverse or tortional deflections.

It is usual for the top stone to be the runner, but several arrangements are made with the bottom stone as the runner. The position of the spindle may be either above or below the running stone. The usual position is below. For stones applied in the reduction of vitreous substances, the top position has advantages, as in that case, all the bearings and drive are clear for injury. With an under runner the spindle below, there is the advantage of having free and clear opening in the eye of the upper fixed stone for feeding. A balanced running stone with the usual free irons works better than a runner on fixed irons, the adaptability of the latter being considerable destroyed, except for very coarse work.

SPLINES. These are templates to mark off the furrows and lands.

STAFF. This is required for truing the face of stones. When used it is coated with a semi-liquid paste, so that the prominences on the stone may be indicated. An annular iron staff is superior to a straight hard wood one. The straight hard wood staff is called a "paint staff," and the iron staff is called the "proof staff." The proof staff is used to keep the paint staff true and is only used as a gauge instrument.

SWALLOW. Various forms are shown in the second drawing.

TIME (Removing and Refixing). The time required to remove the stone, brushing, rubbing, cleaning, staffing, dressing, cracking and refixing may take from 4 to 8 hours, depending upon the quality of the stone and appliances used.

TOE BEARING. The toe must be of such diameter that the pressure upon it does not exceed 260 pounds per square inch, with ordinary lubrication, to avoid any expulsion of the lubricant and consequent hearing or seizing. The lubricant should circulate, and a single diametrical groove under the toe has been determine upon as most efficient. The weight of a 4.0 millstone with spindle and all parts attached to it make be taken at 2,300 pounds, and assuming the bearing to be 3 1/2 inches diameter the pressure will be about 240 pounds per square inch., See the results of some experiments on the bearings published in the Proceedings of the Institute Mechanical Engineers, 1891.

Ball bearings have been about perfected and applied to many machines. Figure 4 in the second drawing, shows a form for and thrust only, and is made by the Hoffman Manufacturing Company, Limited, Chelmsford, England. The steel balls being 5/8 inches diameter, to take safe working pressure of 2,500 pounds at 120 to 150 revolutions per minute. A pedestal or journal close above this bearing is necessary to take the side thrust and to hold the spindle concentric. A heavy lubricant or, if flooded in oil or an oil bath, may be used. The friction is about one-tenth that of ordinary bearings.

TRUNNION SOCKETS. These are fixed about 6 inches from the face at opposite points of a diameter passing through the center of gravity of the stone and receive the trunnions or pins on the crane bows (bails), upon which the stone is supported and turned for inspection, dressing, etc.

VENTILATION. To prevent or lessen undue trituration of the material, wind under a pressure of about one inch of water is applied at the eye which, flowing through the furrows catches up the finer stuff, and with the assistance of the centrifugal action conveys it to the surrounding space between the cover and the stone, absorbing excessive moisture, and cooling the material and the stone surfaces, decreasing the duration of the treatment, increasing the output, and with some materials, leaving it in a better condition for dressing. To a small extent the power required for working the stones is reduced.

Another arrangement included the use of a suction fan connected to the casting. A flexible sleeve or tube attached is required at the eye to isolate the eye form the casing space.

ZONES OF FACE. These are, beginning at the eye, the swallow, the bosom, breast, and skirt. At the swallow the feed enters and subjected to its first treatment, is further softened (reduced by increasingly more furrows) at the bosom, and the operation of reduction completed at the skirt as shown first drawing. The outer periphery of the stone is the verge. This is called "the flouring of the stone" where the stones come very close together and where the actual flour is made.

The angular velocity of a 4.0 stone at 120 revolutions per minute or 2 revolutions per second at a radius of 12 inches is 12.5 feet per second; at 18 inches about 19 feet per second, and at or near the skirt, 25 feet per second; and a particle of feed passing between the stone will be subject to cutting or tearing forces, applied at these velocities.

NOTE: REMEMBER THIS IS ENGLISH! Some terms are different, and others that may be the same, but are spelled differently than American milling terms. The above text has been edited for technical errors.

The above book does not contain a "Table of Contents." However, it is usable by its index. The book is a collection of articles loosely bound together, and does not flow very well. It is of little practical use. James Donaldson is the implied author.

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