The interior of a windmill

You have by now learned to tell the different types of mill apart from a distance and have inspected their exterior features at close quarters.

You will doubtless have realized the effect of tranquillity, self-assurance, power - and splendour - of a windmill on its surroundings. The mills will have fascinated you so much that you will also wish to learn more about the mysterious interior equipment.

Have you ever entered a working corn mill? You should really do so, for you will be delighted with the romantic atmosphere created by the whirring and vibrating, the rumbling, the creaking and groaning of the timber; all this is to be heard in the dust-covered interior of the mill, which does its work though one cannot really see whence it gets the power for it. It seems to generate this power of itself, for at first sight one can hardly imagine that the noiseless breeze passing so imperceptibly over the land does all this.

It is the same thing as with a sailing-vessel (for that matter, there are many points of resemblance!), in which we experience the beneficial effect of gliding silently, without any engine noise, through canals and lakes, at one with nature around us, accompanied only by a solitary bird uttering its cry.

As the sailing-vessel is to the puffing cargo steamer, so is the working windmill to a factory interior.

It is now time to learn exactly what this mechanism looks like.

We have already seen that in the top of the mill's cap is mounted the wind shaft, slightly inclined from front to rear; in front the shaft is supported in the neck bearing, which in turn rests on the breast beam, a strong beam forming a part of the cap structure. The tail of the shaft is supported in the tail bearing resting on the inner tail beam; and at the end of the shaft is the thrust flange which takes the thrust on the shaft and prevents it slipping backwards.

Wind shafts used to be of wood and very heavy; in the poll end there were two large square openings, at right angles to each other. The stocks were passed through these openings and were firmly secured with the aid of wooden wedges. The stock nearest to the mill body is the 'inner stock', the other is the 'outer stock'. More than a hundred years ago the wooden shafts began to be ousted by iron ones. In that case the poll end is a casting, provided in the same way with two large square openings for the stocks to pass through.

Mounted on the wind shaft is the brake wheel, a wheel with a large number of cogs. The rim of this wheel is of heavy construction and is surrounded by a ring of heavy wooden blocks which are kept together by means of an iron band.

This ring of brake blocks constitutes the BRAKE, by means of which the wind shaft can be braked and stopped. To achieve this, one merely has to contract the band with brake blocks about the wheel.

This problem was formerly solved in an ingenious way. When we look at the figure, we find the brake catch, a flat iron having the form of a scimitar and adapted to swing about a point of suspension.

The principle of the method of operating the brake.
When the brake rope is pulled, the brake catch swings from right to left, so
that - in the meantime - the brake lever can be lowered,
the brake clasps the brake wheel, and the mill stops.

A pull at the brake rope causes the brake lever to rise and thus, by means of the pin in the slot of the catch, makes the latter move to the left. During this movement the brake lever is quickly lowered and by its own heavy weight contracts the brake band on to the wheel.

If the brake is to be taken off, one merely has to pull the brake rope slowly; the brake lever is then slowly raised and the pin moves upwards along the catch, past the slot. When the lever is then slowly lowered, the pin will automatically drop back into the slot of the catch, thus taking up its position at rest, so that the brake lever is fixed in its highest position and the brake band remains clear of the rim of the brake wheel.

Now that we are up in the cap, we can see how the cap is supported on rollers which make it possible for the cap to be turned. The rollers, placed within two concentric rings, remain equally spaced; they are all directed radially towards the centre of the mill and run on tracks above and below them. In a brick tower mill the curb, supporting the lower roller track, rests on the brickwork and in a wooden mill on the upper sill, i.e. the beams connecting the upper ends of the wooden corner posts of the mill body. The upper roller track is fixed to the cap circle and the whole is enclosed by a circular wooden band.

The large brake wheel drives a smaller gear wheel, the wallower (cogs in a flange or staves between two disk-shaped flanges), which is mounted on the upright shaft and causes it to turn.

In the drainage mills we found the rotary motion of the wind shaft to be transmitted below to the shaft of the scoop wheel or of the Archimedean screw. In corn mills the upright shaft on the stone floor carries a large spur wheel, which drives the smaller stone nuts, of which there are two, three, or sometimes even four.

Between the top floor and the stone floor is the bin floor; this is the floor where the SACK HOIST is to be found.

The sack hoist consists of a drum with a gear wheel, driven by a separate wheel on the upright shaft. These gear wheels can be made to mesh or be disengaged as desired. Thus it is possible to drive the drum at will by the power of the mill and to hoist the sacks of grain from below with the aid of the rope wound round the drum.

The actual grinding of the grain takes place between two big MILLSTONES, which are enclosed in a wooden casing. The contact surfaces of the stones are provided with spiral furrows. The lowermost stone, the BEDSTONE, is stationary and the uppermost stone, the RUNNER STONE, revolves above it. The runner stone has a hole in the centre, the eye. A bin, mounted on a floor above it, feeds a hopper, and from the hopper the grain falls into the shoe and thence into the eye of the runner stone. It is ground between the stones, moves through the furrows to the outer edge, and passes as meal through the casing.

A wooden spout communicating with the casing conveys the meal to the meal floor beneath, where it is collected underneath the discharge opening in sacks, ready for transport.

These wooden spouts can be shut off at the lower end by means of wooden gates, which can be raised.

The bedstone is kept in place on the stone floor by means of wooden clamps. The quant has to drive the runner stone and thus has to be firmly anchored in it. This is achieved by means of a rynd, i.e. a cast-iron cross with equal arms, having in the centre a square opening for the cock-head of the spindle to pass through. The four arms are let into the stone and cemented into it.

Tentering: the adjustment of the gap between runner stone and
bedstone is shown in the diagram

It is this part of the mill which is very familiar in heraldry in numerous escutcheons of families which were associated in one way or another with a windmill. Several variations of it exist, generally in a form with slightly concave arms.

The mill rynd in heraldry

In a strong wind the power of the mill increases, it will be able to grind larger quantities than in a slack breeze. In order to make use of this greater capacity, the gap between the stones has been made adjustable, so that it is possible, dependent on the available power, to admit larger or smaller amounts of grain between the stones, thus regulating the load and increasing the output.

This adjustment (tentering) was carried out in a very simple, but ingenious way. The runner stone rests on the bridge tree via an iron 'stone spindle' passing through the bedstone. One end of the bridge tree is hinged to the wooden framework of the mill and the other end is held up by means of a suspension system in such a way that the weight of the millstone is balanced as much as possible by a counterweight. The force required to move the stone up or down is thus only slight. One merely has to raise or lower the cord a little if one wants to raise or lower the runner stone.

Later on, an automatic centrifugal governor came to be used for this purpose.

The drive of the stones is also turned to account to vibrate the shoe, so that the flow of grain cannot be interrupted, but will continue uniformly.

The stones have a diameter of some five feet and a thickness of twelve inches. They used to come from the volcanic regions of Germany and the quartz beds of France; owing to their constitution they were porous and consequently had good cutting properties. For some purposes, millstone grit was sometimes used and later on composition stones.

The sharpening of the furrows is called DRESSING and this is a highly skilled job; the grade of the meal largely depends on it. When the stones have been used for some time, they become dulled and have to be dressed. For this, the runner stone has to be raised, which is a heavy job in the cramped space available for it. The dressing itself takes place by the light of an oil lamp hanging over the stone, for the poor daylight entering through the small windows of the mill is on the one hand too scanty to allow proper work and on the other hand causes cast shadows, which would make dressing even more difficult. The shutters are therefore closed.

For the dressing operation use is made of special hammers, called bills, drawn out to a chisel point at each end. It is self-evident that dressing was a difficult and lengthy job and formed an important event in daily mill routine; all that time no grain could be ground. By means of the position of the sails the miller would inform everybody in the neighbourhood that the stones had been raised, so that for the time being no grain could be accepted for grinding.

The governor, which automatically adjusts the distance
between bedstone and runner stone

In barley mills and rice-hulling mils, HULLING STONES were used instead of millstones. They were somewhat larger than the common millstones and the casings were also constructed a little differently. The barley or rice did not have to be ground but was hulled, i.e. the thin outer covering of the grains had to be removed. The stones were usually gritstones and the runner stone had only a few deep and wide furrows, through which the grains were flung out as the stone revolved, without being ground between the stones. The wall of the casing was lined on the inside with tin sheeting, in which holes had been beaten in such a way that the sharp points were turned inwards, thus forming a cylindrical grater. The grains were flung against it and rubbed by the circular edge of the stones, freed from their hulls or shells, and smoothed. Whilst barley, used to be a favourite national food, in the early part of the nineteenth century it was replaced more and more by imported rice; this rice too was treated in the hulling mills.

For the grains to be flung out it is necessary that hulling stones should revolve faster than millstones; it was a heavy job and hulling mils were powerful mills, which required a strong wind for operation. It was possible to use a higher or a lower gear in the mill, as desired, according as the speed was low or high.

Instead of a sack hoist such mills often contained an elevator buckets on an endless belt - which lifted the barley and regularly poured it into the hoppers.

For all the additional work a third spindle was present, taking its drive from the upright shaft via a separate gear wheel.

Besides mills for grinding and hulling there were also OIL MILLS for pressing oil from seeds, MUSTARD MILLS, and the like, as well as mills in which all sorts of coarse and hard materials were ground fine. The last category includes the mills which made dyewood into DYE, the CHALK MILLS, the TRASS MILLS, etc. This grinding operation took place in a kollergang (an edge mill), i.e. a couple of runner stones rolling on their edges in a stone pan.

The principle of the kollergang or edge mill,
two edge runner stones rolling on the pan, with wooden guides

The stones are mounted on a shaft, which is driven by the stone spindle from the spur wheel. There is an outer and an inner stone, the latter running about 8 inches closer to the spindle, so that a broad track is covered by the two stones. The seed is pulverized between the heavy rolling stones and the pan underneath. A couple of curved wooden guides following the motion of the stones ensures that the seed rolled out under the stones is promptly returned to the track of the runners.

When it has been pulverized sufficiently, the meal is brushed together and poured into a receptacle underneath through a gate which can be opened. We shall discuss the further treatment of these oil-seeds in oil mills later on.

The most important parts of the interior equipment of a TIMBER SAWMILL are of course the SAW FRAMES, i.e. the wooden frames with saw blades, which are reciprocated by the movement of the mill.

Crankshaft and saw frames in a sawmill (after Krook)

In the upper part of the mill there is a horizontal crankshaft, which is driven by means of the gear wheel mounted on it, the crank wheel. The rotation of the wind shaft is transmitted via brake wheel and wallower to the upright shaft, and further downwards the upright shaft carries a crown wheel, which in turn drives the crank wheel.

When three cranks are present, they are placed at 120o to each other, so as to ensure as uniform a distribution of forces as possible.

Vertically suspended from each of the cranks is a connecting rod, the lower end of which is fastened to the saw frame. To the left and the right of each crank the crankshaft is supported in a bearing block in which the shaft is able to rotate while at the same time being firmly held in it.

As a rule there is one large saw frame, about 4 feet broad and 6 feet high, located between the front of the mill and the upright shaft, and two smaller saw frames at the back. Mills of the paltrok type usually have two saw frames, one on each side of the upright shaft; for balancing purposes the third crank is then used to move up and down a dummy frame, which has the form of a case containing weights; the latter is placed on the frame floor, above the saw frames.

Occasionally there are four saw frames in a sawmill, two in front and two at the back.

A saw frame is a strong wooden frame consisting of two uprights which are connected at the top and the bottom by the heavy tensioning beams. The saw blades are tensioned between them. Above the upper tensioning beam there is another connection between the uprights, the cross-head; to the latter the connecting rod is fastened. Because the upper end of the connecting rod performs a rotary motion, it is necessary that the point of application of the connecting rod on the saw frame should be able to make a small pivoting movement. This is made possible by the cross-head; it has been let into the uprights by means of pins.

The whole saw frame is moved regularly up and down by the cranks via the connecting rods. The lower tensioning beam in its highest position always remains some four inches beneath the sawing floor.

The big frames serve to cut up the thick baulks and logs; this is done in smock mills, which are stronger than mills of the paltrok type. The latter saw wainscot, the smock mills saw baulks.

The baulks, logs, and boards to be sawn are lashed up on a carrier moving over the sawing floor of the mill, each saw frame having its own carrier. Sometimes a set of rollers is found instead of a carrier.

The sides of the saw frames slide in grooves of lignum vitae, so that they are forced to reciprocate vertically. At the downward stroke the saw makes its cut and with the upstroke the carrier with the timber to be sawn has to be advanced slightly. This movement is performed with the aid of the TIMBER FEED. This consists of a shaft, on which are mounted a small pinion and a large toothed wheel, the ratchet wheel; the latter has a great many oblique teeth. The teeth of the pinion mesh with those of the rack, i.e. a long and straight iron with a series of teeth on it, which in the central part of the carrier is integral with it.

Simultaneously with the motion of the saw frame a reciprocating lever moves the end of an arm up and down, so that with each stroke the ratchet wheel is advanced by one or two teeth and the carrier correspondingly is advanced a little with every upstroke.

On the frame floor there is a separate similar ratchet wheel, which provides in a similar way for the rotation of a wooden roller round which the crane rope or a towing rope has been wound. The crane rope passes over the pulley in the crane outside, and in this way it is possible in mills of the paltrok type to hoist the logs and baulks from the water by wind power. Similarly in the smock mills the baulks are dragged from the water with the aid of the towing rope and along the slipway on to the sawing floor, so that they may be deposited and fixed on the carrier. A ratchet mechanism again ensures that the roller cannot rotate backwards of its own accord.

The timber feed of a sawmill (after Boorsma)

We will now return once more to the OIL MILLS, the edge runner stones of which have already been discussed.

The task of these mills was to press oil from the different kinds of seed: coleseed, linseed, rapeseed, and sometimes also hempseed. These oils were indispensable to daily life at that time, and they served for the most varied purposes: for human consumption, for technical purposes, for lighting (rapeseed oil for the old-fashioned oil lamps), etc.

In the oil mill the seed was first crushed under iron cylinders and then ground and rubbed in the edge mill. After having been heated, if necessary, it was pressed by means of rams and pulverized by stamps.

A single-working mill had, in addition to the couple of stones, one set of rams and three stamps. Most mills, however, were of the so-called double-working type: two sets of rams and six stamps. There were even a few mills equipped with two clouble mechanisms. All these RAMS and STAMPS, like the edge runner stones, are driven by a system of gear wheels from the main shaft of the mill.

Method of driving rams and stamps of a double-working oil mill.
Above left: the method of lifting the rams and stamps

By the side of the edge runner stones there was a fire-place, built of fire-bricks; this was fired with peat and served to heat the ground seed, the meal, in advance. Opposite the fire-place was the pressing block for the first operation.

The heated meal was put in a woollen bag, which was packed in a horsehair cover in the form of a kind of mat. During the pressing operation the oil was able to escape through the numerous pores of the fabric.

The package was put in the cavity of the first pressing block intended for it and locked in it with the aid of spacing blocks. These included two wooden wedges, one of which was inserted with the thick end up and the other with the thick end down. The former was the pressing wedge, the latter the releasing wedge. Above the block hung the two rams, the striking ram and the releasing ram.

The striking ram was then put into operation and through the numerous strokes on the pressing wedge the contents were greatly compressed in consequence of the wedge shape. This operation was not allowed to take place too quickly, for the oil had to have time to flow off through all the pores into the receptacles underneath. In view of this there were only two cams on the cam shaft for the first pressing ram.

Oil pressing

After fifty strokes the mass had been pressed sufficiently and a few blows of the releasing ram on the releasing wedge sufficed to remove the spacing blocks, and the mass, which had become a cake, was taken from the bag. The cake then still contained some oil, but this was removed from it by the second pressing operation. For this purpose the cake was broken up and pounded in the pots underneath the stamps, and, after being re-heated, it was subjected to the same treatment again in the second pressing block.

When all the remaining oil had thus been removed, the cake, which still contained a few per cent of oil, could be removed and stored, to be sold as cattle feed.

The correct number of the strokes with the ram was checked by means of a bell, which was operated by a ratchet system after a given number of strokes had been set, and which then, amidst the deafening noise of the stamps, warned the attendant that it was time to 'release'.

An oil mill at work, with its frequent booming strokes, could be heard for miles around, and inside the mill the thumping was so terrific that people could not make themselves heard. This frequently gave rise to a special kind of deafness.

An outsider cannot understand how the people living in the neighbourhood could endure such a noise going on night and day, but it seems they got used to it in time and did not hear it any more. They even awoke at night when for some reason or another the mill stopped, and then they were unable to get to sleep again because of 'the unpleasant noise' of the unusual 'silence'!

The interior equipment of the various other types of industrial mills, which have been mentioned more than once, does not differ essentially from the above descriptions, and it would take us too long to discuss all these types in detail.

In the paper mills, milling and stirring mechanisms were driven by rotating shafts, in the dye mills, chalk mills, tan mills, etc., in which some material was pulverized, edge runner stones operated in the way described above. Stamps were used in fulling mills and snuff mills.

Several details have had to be left out of account, but the reader will have got some idea of the way in which the windmills could perform their widely varied task.

One thing, however, of which no description can give an idea, is the very clever way in which the various wood constructions were made by the millwrights in the old days; they bear witness to highly developed craftsmanship. The numerous small details too, so well thought-out and finished with such care, fill us with admiration of the men who with very simple tools were able to construct it all so perfectly.

Anyone interested in windmills will therefore find it worth his while to devote close attention to their interior.

- next chapter -



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