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ARTICLE XVII.
EXPLANATION OF THE SCREW MILL INVENTED
AND PATENTED BY THE AUTHOR.
This mill is intended for breaking all hard substances,
and to prepare them for entering millstones to be pulverized.
No.1 plate II. is a perpendicular section of the mill with the screw set horizontally, which has been found the best position.
A B the screw, which is for breaking plaster at the rate
of 2 tons per hour, is made by twisting a flat iron bar 5 or 6 inches broad,
1 1/2 inch thick, making the screw part 12 or 15 inches long. It is set
to revolve about 40 times in a minute, over a grate fixed in the bottom
of a hopper strongly made and plated inside with iron; the upper corner
of the bars of the grate next to A is made highest, to catch against the
lumps of plaster, to prevent them from slipping too freely before the screw,
which is made to turn so as to drive the plaster towards B, and causes the
screw to press hard against the steel plate A, fixed there to keep the screw
steady to its place. The plaster, in large lumps, is thrown into the hopper
at C, and broken by the stroke of a large hammer, so that the screw will
take hold of it, and as it is broken by the screw it falls through the grate
D, and is guided by a sloping spout B E into the millstones, or into an
elevator, to be raised to the millstone hopper. A screen may be set in
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the bottom of this spout to let all that the screw makes sufficiently fine, pass through, to be guided by a second bottom F to the proper place, without passing through the stones.
G H a fly wheel on the shaft, connected with the screw to give it motion. This fly is necessary to regulate the motion of the screw, and by its momentum to overcome all extra resistance, occasioned by large or hard lumps, and to equalise the stress on the cogs of the wheels which give the motion.
No.2 represents a perpendicular plane section of a screw
mill with the screw set perpendicular, to revolve in a hopper closed at
bottom so as not to suffer lumps of too large a size to pass through. The
bottom part of this hopper may be made of cast iron fluted or furrowed,
so as to prevent the substances, to be broken, from sliding round with the
screw; or it may be open, in form of a grate, to let the lumps pass through,
when sufficiently reduced. Or a hole may be made in a stone to form the
lower part of the hopper. Or the upper millstone may be made stationary,
and the lower one made fast to the screw, to turn and perform the grinding
in this case, the eye of the upper stone forms the lower part of the hopper.
Or the millstone may be set vertically, instead of horizontally, and the
screw set horizontally to run in a hopper but without a grate, as in No.1,
the screw passing through the eye of the stationary stone, and made fast
to the running one, then turning the screw turns the stone, and the screw
drives the substance as broken, through the eye of the stationary stone,
in between them to be ground, which does
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very well. I made a handmill on this simple structure,
with which I had several thousand bushels of plaster ground by hand; it
is perhaps the best handmill for that purpose: the running stone is much
larger than the stationary one, and serves the purpose of a fly. This mill
I sold for the purpose of breaking charcoal for a steel furnace, for which
it answers very well. The millstone is fixed at the end A, and the crank
put on B, and turned so as to drive the plaster or coal, &c. as broken
between the stones: its simplicity renders it the more useful; it has neither
wheel nor cog belonging to it: * or the screw may be attached to the cock
head of the spindle of the millstone, when fixed in the common way, and
a hopper put round the screw to break the hard substance and let it fall
into the eye of the stone. This screw mill may be changed into a great variety
of forms and be still on the same principle and be a good machine: but perhaps
no form will be found better than No. 1, for breaking plaster, charcoal,
Indian corn
*This invention I made and reduced to practice during
the winter of 1795-6. It was with difficulty I could find any person willing
to apply it to water-mills. Several years passed before I could prevail
with any one to try it. Mr. John Rhynehart of Chester county was the first
to adopt it; and when he got it a going, he came and advised me to take
out a patent immediately, saying, it was an excellent machine; it answered
so well for breaking plaster, and also Indian corn, with which people came
considerable distances with waggon loads to get ground for their cattle.
It is now getting into pretty general use, and there has at least a dozen
of inventors started up already, all claiming the invention; so easy is
it to invent a machine already in use.
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in the ear, to grind the cob with the grain, for food fot cattle, several kinds of paints, lead and other ores, different kinds of barks, &c. and perhaps no cheaper and more simple machine can be invented for a variety of such purposes.
Those who may wish either to make or use the said mill,
may obtain permission by applying by letter directed to the inventor in
Philadelphia, on paying 10 dollars for the license, for common uses. And
those who make or use said mill, and refuse or neglect to pay for a license,
will be treated as the act of congress in such cases made and provided directs.