le-i'i t.ian the circumference. The blades should
b»^ inclined backward a little instead of being per-
pendicular to the shaft, so as to produce a ten-
dency in the water which they drive backward to
converge to a point. It is assumed that this con-
vergL'ut tendency may balance the divergent ten-
dency ilue to the centrifugal force attending the
revolution ; so that the two forces being in equi-
librium wiU cauiie the water to be projected back-
ward from the screw in a cylindrical column.
As the screw revolves and thrusts backward
against the water, the forward end of the screw-
shaft impinges forcibly against a bearinj;, and
thereby impels the ve.-isel. Thi^ pressure is very
Severe, as may be readily imagined, when it is con-
nidered that the forward pressure is driving the
vessel through the water. One device for receiving
this forward thrust is a number of collars or
disks placed at the end of the shaft and resting in
a cistern of oil, which is firmly supported in the bed-plate of the
engine, or some other place sufficiently strong. Between the
end of the cistern and the sh ift the disks are interposed, and
are free to revolve by the frictional pressure of the screw-shaft.
If the end of the shaft press with such violence against the disk
as to become hot in revolving against it, and engender such
friction as to carry the disk along with it, then the first disk
revolves ag;Linst the second, and the surfaces previously en-
gage.!, no longer rubbing against each other, have time to cool,
and resume their efficiency.
The screw is sometimes suspended on a short shaft, carried
by a metallic frame having a rack on one side, which is engaged
by endless screws for the purpose of liftmg the screw for ex-
amination or repairs. See also Fig. 4751.
Maud>lay's feathering-screw is so arranged that the blades,
whenever the vessel is put under canviis and the screw not re-
quired, should be placed in a direction parallel with the line of
the keel, and form, as it were, a portion of the dead-wood, as
they cause considerable obstruction, if they are allowed to re-
main fixed in thL'ir position, even though they be disconnected
from the engine and allowed to revolve. In auxiliary sailing-
vessels not titted with a trunk or screw-well for raising the screw
out of the water, tliis is particularly valuable.
c and d are modern forms of screw-propellers, having respec-
tively three and four blades.
The number of blides of a screw should depend on the area
of propelling surface in proportion to the length of screw on
the line of the keel. The width of blades is reduced in pro-
portion to their number.
The pitckoi a screw is the distance it should advance in an
axial line by one complete revolution, provided no force be lost,
:us would be t.ie case in an unyielding medium. The rate is
the nctuid advance, and the difference or loss is called the
The slip varies with the angle of the propeller, its velocity,
and depth of immersion. The coarser the pitch, the greater
the slip
The friction of a screw depends on its velocity and the smooth-
ne.ss of finish of the material of which it is composed.
Tne vibration depends on the form and uniformity of resist-
ance
The thrust of the screw is the force exerted on its shaft to pro-
pel the vessel. This thrust is generally taken up by friction-
collars on the screw-shaft.
The pitch of a two-bladed screw should in general equal IJ
diameters; a three-bladed screw, li diameters; a four-bladed
screw, 1 di.imeter.
The actual force exerted by a screw depends, to some extent,
on its depth of immersion. The indinaiion of the screw should
be such as to overcome the tendency of the body of water acted
upon to rise to the surface.
Experiments h ive indicated that paddle-wheels give the best
result when the vessel is lightly immersed, and the screw when
deeply immersed.
Experiments made by the British navy tend to prove that
the best results are obtained when the screw is entirely free
from back-JJow or '/ea^/-water ; also that a screw inclosed in a
pipe or box open at the ends has much less eBective force than
when it is not so inclosed.
Many and various devices have been patented in this country
and in Europe, intended to overcome the loss from slip and from
friction. Among these may be mentioned the duplex or reverse
screw, having an inside shaft and aujciliary screw back of the
one on the main shaft, the two screws moving in opposite direc-
tions. For some other modifications of the screw, see Pro-
peller.
Fig. 4749 illustrates a new arrangement in use on the steam-
ship "Britannic," of the White ^^tar line, enabling the pro-
peller to be raised or lowered, and still be in a position to re-
ceive motion from the shaft. The shaft is in two parts a b.
Fig. 4749.
Propeller of " Britannic " ( White Star Line).
coupled at c by a universal joint ; and the upward or downward
movement of the propeller is effected by a pinion gearing in the
nick d jointed to the rear part of the shaft. Water is prevented
from entering the ship by a device consisting of a disk e through
which the shaft passes pivoted within a second disk/, which in
turn is pivoted within a casing forming part of the shaft-well,
the joints being suitably packed. When the rear portion of
the shaft is raised or lowered, it and the disk e turn on the uni-
versal joint as a center, causing the disk/" to rotate on its axis
and around the disk e until the propeller assumes the desired
position.
Mr R. GriflBths, of I/Ondon, well known in connection with
propellers, has recently proposed to employ a screw placed
within a tunnel both at the bow and stern ; from trials with
models he concludes that an increase of nearly 50 per cent in
speed can be gained with the same power.
A small boat employed at Burlington, Iowa, for crossing the
Mississippi, 50 feet long, 7 feet beam, drawing 30 inches aft and
1 foot forward, and propelled by a 4-foot propeller, attains a
speed of 10 to 12 miles up stream, and 15 miles down stream.
She has a locomotive boiler 11 feet long, with fire-box 2A X SJ
feet, and 27 !^-inch flues, 7 feet long. The two engine-cylinders
are direct-acting and vertical, of 5 inches bore and 13 inches
stroke, and are fitted with circular slide-valves. The usual
amount of steam carried is 80 pounds ; number of revolutions,
133 per minute.
Screw-pro-peller Gov'em-or. {Sieam-en-
gine.) One in wliicli the action of a .screw-propeller
device, working in a resisting fluid, is employed to
regulate the throttle-valve. In Huntoon's (Fig.
4750), the pulley-shaft a, driven by belt connection
with the engine, carries a gear-wheel b meshing with
a long pinion on the shaft of a screw c, inclosed in a
tight box tilled with oil or water, and causing its
rotation. The apparatus is so adjusted that when
the engine is workiiig at its normal speed, the lever
d just balances the tendency of the propeller-shaft to
move forwai-d under the inlluence of the screw, and
no movement of the valve e takes place ; should the
speed diminish, the weight overcomes the resistance
of the screw, and the valve is opened ; if the speed
exceeds the regulated amount, the forward move-
ment of the propeller-shaft, acting again.st the arm
d\ causes the weight to rise, partially closing the
throttle.
Screw-pro-pel'ler Steam-en'gine. A direct-
action steam-engine, specifically adapted for the ro-
SCREW-PROPELLER STEAM-ENGINE. 2073
SCREW-STEERING GEAR.
Fig. 4750.
Huntoon^s Serew-Propelkr Governor,
tation of the screw-propeller shaft. The form of
engine most commonly used for this purpose is the
OsCILLATIXG-CYLIXDER ENGINE (which see).
Maudslay's direct-action screw-propeller steam-
engine was especially designed for dispensing with
the multiplying-wheels, or chains and drums, be-
tween the engine-crank and the shaft of the screw-
propeller, in order to give the latter sufficient speed.
The engines are ranged side by side in a line coincident with
the line of the propeller-sliaft, and immediately over the engine-
shaft, which is concentric with the propeller-'^haft, and is con-
nected thereto by a coupling, by which the machinery and
screw-shaft may be disconnected when the vessel is to be driven
by sails alone.
Fig. 4751.
The engines have a short stroke, a is the cylinder, sup-
ported on the upper part of the condenser 6 and on a projecting
flange on the air-pump c. The engiue-crank is beneath the
cylinder, and to it is connected one of the cranks d of the shaft.
The crank is driven by a connecting-rod from the cross-head
above the piston-rod and piston e. The slide-valve is cylindri-
cal, and has an oscillating motion, the peripheral depres.«ion
forming a port by which the ends of the cylinder are alternately
connected to the condenser 6. while the internal ports of the
valve form the induction steam-passage leading the live steam
of the boiler to the alternate ends of the cylinder.
The foot of the air-pump is inserted in a flat prolongation of
the condenser ; and the foot-valve / is at the bottom of the
pump. The delivery-valves in the pump are composed of an-
nular plates, which rise and fall vertically between guides, and
admit of the escape of air and water around the periphery and
at the central aperture. The upper portion § of the air-pump
lorms the hot-well from which the supply for the boilers is
drawn by the feed-pump, and the surplus passes off by the
waste-water pipe. The air-pump is worked from the parallel
motion, consisting of the working-beam A, connecting-rod i,and
other associated parts, as seen in the figure.
Scre'vir-punch. A punching device operated by
a screw. In that shown, two
screws C D are used for for- Fig. 4762.
cing the punch, one screwing
into the first with a finer
thread, so that when the
larger or outer screw is
turned, the inner one, being
held from turning by a
squareshaukpassingthrougli C$ i«, ^
a stjuare hole in the stock, '^
screws into it, and therefore
e.ferts a slow and powerful
downward movement. See
also PnNCHING-BE.\R.
Screwr-rud'der. An ap-
plication of the screw to
purposes of steering, instead
of a rudder. Tlie direction
of its axis is changed, to give
the required direction to the
vessel, and its efficiency does Scrrw-PuncJi.
not depend upon the motion
of the vessel, as with a rudder, and the vessel may
be turned on itself even when not under way.
Screw-spike. A round spike having a shallow
screw-thread cut on a portion of its stem. It is
driven partly home and screwed the remaining dis-
tance. See Spike.
Scre^-steara'er. One propelled by a screw,
in contradistinction to a paddle-wheel steamer.
Screw-steer'ing Gear. A screw on the axis
ofthesteering-
Maudslay's Screw- PropelUr Steam-Engine.
wheel may be
matle to act
upon the nid-
der-head
through the in-
tervention of
nuts, or nuts
and rods.
M 'Williams's
gear (English)
operates by
Fig. 4753.
Screw- Steering Gear,
means of a light and a left hand screw d e on the
axis a of the steeiing-wheel. //are two tiaversing-
nuts, and h h two traversing-rods, parallel to the
spindle, and fixed respectively to the two traversing-
nuts at i i, and each passing through a guide-eye in
the other nut. k k are two links jointed respectively
a.tjj, to eyes on the traversing-rods, and at 1 1 to
the two arras of the yoke, b is the rudder-head.
A modified form of screw-steering gear was intro-
duced by Reed (English). It has a similar right
and left screw operating nut-blocks, which slide on
parallel guide-bars. Each nut-block has a pin
which engages iu a slotted lug on the cap of the
SCREW-TAP.
2074
SCREW-THREADING MACHINE.
ruddei-liead, and thus turns the rudder when the
screw-axis is rotati'd. See Steeking.
Scre'w-tap. An instrument for cutting tlie in-
terior thread on a hollow surew. For cutting the
corresponding thread on the screw rod or bolt, a
screw [date or dies are employed.
These are held io a dU-stock, aa improved form of which is
shown at a. This is adapted to receive dies having dilferent-
sized threads, which are held by a screw ; the sides of the open-
ing being plaiu at one end for the ready introduction of the
Fig. 4754.
threads on bolts or rods. See also Screw-machine ;
ScUEW-LATHE ; TUKKET-LATHE, etc.
In Fig. 4756, the surew is received in the holder i
of the feed-head k, and clamped by a gage m'. The
feed-head is advanced by the bent lever P engaging
the ratchet-bar R to meet the dies which are held by
die-holders g secured in the cutter-head A". When
the thread has been cut to the deteriniued length,
the end of the screw strikes the end o of the rod n
Pig. 4756.
Screw Taps and Dies.
dies, and having ribs at the other, which fit grooves in the dies
and prevent their > falling out when fixed, c d illustrate the
action of the common two-part die on the rod placed centrally
between its parts, in the first the die has the same curvature
as the finished screw ; in the latter that of the uncut rod. In
either ca-«e but a part of the cutting surface acts, and the ten-
dency is to cut an imperfect thread.
This is partially remedied by cutting the dies of a curvature
intermediate between the two.
To obviate this defect as far as po.ssible. Sir J. Whitworth
introduced the arrangement shown at e.
The two narrow dies act as cutters, and are advanced toward
the center of the rod on which the thread is being cut by turn-
ing the thumb-nut o, which advances the slide-piece p ; the
broader die opposite serves principally as a guide for the thread.
/are tools for chasing exterior threads, and g for interior
threads on work held in a lathe.
A is a section, and i k elevations of taps : these have a square
shatrk fitting in an appropriate holder like the die-stock, or
sometimes the die-stock itself is adapted for this purpose.
b is the screw-plat« ; this is principally used for small worK,
and has a series of screw-threaded apertures of various sizes
adapted for different-sized wire.
Screw-thread Gage. A gage for giving the
proper bevel to the edges
of screw - cutting tools.
That illustrated is adapted
to the system recommended
by the Franklin Institute
and adopted in government
1 establishments. The angles
are of 60", and the Hat sur-
faces at the top and bottom
of threads are equal to one
eighth of the pitch.
Screiw-thread'ing
Saew-nr,id Gagf (am- Ma-ohine'. A machine
half Size, Linear). for cutting or chasing
Fig. 4754
Screw- Threading- Machine.
within the hollow shaft / which rotates the cutter-
head, forcing the rod back and permitting the dies
to open and release the screw.
In Fig. 4757, the screw blank or bolt is clasped
Fig. 4757.
^.^
y
Screvf' Threading Machiiu.
SCREW-TOOL.
2075
SCRIBBLER.
w
m
w
between two jaws held in the stationary head G by
set-screws, and i otatiou is imparted by bevels, gears,
and a winch. The dies are held between the pivoted
jaw K and movable head M, which slides on the rod
o aiid advances as the thread is cut.
Scre^r-tooL For
Fig. 475S. wood-turning.
For soft wood : —
a, outside screw-
tool.
b, inside screw-tool.
For hard wood or
ivory : —
ScTeiD- Tools. c, outside tool.
d, inside tool.
Screw-tube Fit'ting Fig. 4759 illustrates fit-
tings for gas, water, and steam pipes of wrought-iron.
Fig. 4759.
a a, Pockets.
b b b, bends,
c, nut.
tf , cross.
e. main cock.
Screm- Tube Fating.
g, elbow,
h, pipe tongs.
Scre^v-valve. A faucet or stop-cock whose
valve is actuated by a screw. See Stop- valve.
Screiw-ven'ti-ia'tor. A ventilating apparatus
in the form of a screw, which is rotated by the pass-
ing current of heated air. It can hardly be said to
be a mechanical ventilator, as it is only operated by
the air in the discharge-aperture and does not drive
the air through. It may be so arranged as only to
rotate in one direction, and thus to impede the back
pa.ssage of air while it yields to its discharge.
Screw-well. (Shipbuilding.) A hollow in the
stem of a vessel into which a propeller is lifted, —
after being first detached from the shaft, — when
the vessel is to go under cauvas alone.
Screw-wheeL The .same as Worm-wheel
(which see).
Screw - wire Fas'ten-ing. (Slwcmaking.) Alao
known as cable-screw wire. A twisted wire for
fastening soles and uppers together ; a substitute for
pegs or stitches. Boots and shoes made by this
process have their soles fastened by a flexible wire,
twisted into the form of a screw, which an in-
genious machine cuts off in proper lengths and
drives in without the preliminary punching which
has always been considered necessary. The machine
is capable of putting on five hundred pairs of soles
in a day. See Nailing-machise, pag^ 1507 ;
Wire ; Wip.e-peggek, etc.
Screw^-wrench. 1. A spanner fitting the
square head of a bedstead-screw. A turn-screw.
2. A wrench whose movable jaw is ojiened and
closed by a screw.
Fig. 4760 has a sliding jaw adjusted by a screw.
Fig. 4760.
Angle-Wrew'S.
Its shape enables it to be applied to bolts in deep-
seated places, not readily reached by the ordinary
^vrench.
Fig. 4761 shows several varietie;;, which do not
need detailed description.
Scribtet. A painter's pencil.
Scrib'bler. (Cotton and Woolen ifanufacture.)
A carding-machine by which fiber is 1 oughly carded
preparatory to the final carding. A scripliiig- machine.
Fig. 4761
Screw- Wrenches.
SCRIBBLING.
2076
SCROLL.
Scrib'bling. {Cotton and Woolen Manufacture.)
The tiist rough carding, preparatory to the final card-
ing.
Scrib'bling-en'gine. (Woolen Manufacture.)
A form of cardiiig-fngiiie for fine, short wool, hav-
ing one main cylinder, and having, in lieu of the
top cards, numerous small rollers lying and rolling
ujion its vipper surface.
Scrib'bling-ma-chine'. ( Woolen Manufac-
lurc.) A machine in which oiled wool receives one
or more preliminary cardings before jiassing through
the regular carding-machine. It is a somewhat
coarser process tlian carding, but of the same nature ;
its purpose being to bring wool to a broad, thin
fleece or lap. It corresponds to the breaker lor cot-
ton. See e'ARDIiNO-MAOllIXE.
Scribe-awl. An awl used for marking lines to be
followed in sawing or cut-
ting out work. Called also
scribcr, scribing-awl,
srrafch-awl.
Scrib'er. A carpenter's
marking - tool. A scribe-
a wl.
Scrib'ing. The fitting
of the edge of a board to
another suiface, as the
skirting-board of a room is scribed to the floor, being
Fig 4702,
:^:^5^
Sril„..iwl.
^\j
marked in position and then cut to match the in-
equalities.
Scrib'ing-com'pass. {Sad- Rr- *763. Fig. 4764.
dlenj.) A compass with one
pointed leg to act as a pivot, and
one scooping edge to act as a
marker. It is especially used to
remove the gum on patent leather
in a line for a row of stitches, and
is set open to any degree by the
arc and set-screw. Scrihing-
It is also used as a scribe in iron.
making a line near the edge of a
strap, one leg passing along the guide-
edge, while the other makes a groove on
the line required.
Scrib'ing-ir'on. A scoring-tool for Compius.
njarking logs and casks. A race-knife.
Scrimp'ing-bar. (Calico-printing.) A grooved
bar which spreads cotton cloth right and left, so as
to feed smoothly to the printing-machine.
Scrims. Thin canvas glued on the inside of a
panel to keep it from cracking or breaking.
Serin. (Mining.) A small vein.
Script. (Printing.) A kind of type in imitation
of writing. Called Anglaise by the French. There
are many varieties, some very beautiful. See also
Seceet.^iit ; Type.
Scribing-
^^Hj/a.
^^^/ii-i-^ ^.?Zt-S ^6* gft;>^ ^-ft- ^=^^1?€^^^^ Qz>^>^ZtX-^^ ^^^e<^ /^€'£ - *2.-»^-£ - f^ in^^ C^^C^C€.^^-CC.
Wl/ i^
Jouv/e- 'Y'i't-nMfp JiofaiifJ.
Scroll 1. (Joiner]!.) An ornament of a form
derived from, and yet distantly resembling, a partially
unrolled scroll of parchment. Instruments arc made
for laying out scrolls and curves for stair-work, and
other irregular forms. See Spikal, Instrument
FOR DRAWINO.
2. (Hydraulic Engineering.) A spiral or conver-
ging adjutage around a turbine or other reaction
water-wheel, designed to equalize the rate of flow of
water at all parts around the circumference of the
wheel, by decreasing the capacity of the chute in its
circuit. See Turbine.
A double scroll is seen in the cut, the valves of
each being operated by a single rod, and two worms
meshing into the segment-racks of the valve-stems.
Each chute supplies
one half the cir-
cumference of the
wheel.
Fig. 4766 shows
by a horizontal sec-
tion the scroll di-
minishingin section-
al area as it passes
around the wheel.
3. (Ship.) A
piece or pieces of
timber bolted to the
stem in lieu of a
figure-head.
Fig. 4765.
SCKOLL-CHUCK.
2077
SCROLL-SAW.
Fig. 47
Fig. 4767.
Turbine and Scroll. Scroll-chuck.
(Lathe.) A de-
vice for holding and centering work in the lathe.
The body of the chuck is formed of three pieces abc;
between these is inclosed a ring tZ, which may be
revolved independently. In the face of the chuck
are three radial grooves, each of which has two
feathers projecting from its sides into the body of
the groove ; the three jaws slide freely along these
grooves and feathers. A spiral on the face of the
ring d enters a counterpart spiral on the inner ends
of the jaws, so that by revolving tlie ring these are
caused to approach or recede from the center.
Scroll-gear. A gear-wheel of spiral or snail form.
See Scroll-wheel.
Scroll-saw. A relatively thin and narrow-
bladed reciprocating-saw, which passes through a
hole in the work-table and saws a kerf in the work,
which is moved about in any recjuired direction on
the table. The saw follows a scroll or other orna-
ment, according to a pattern or traced figure upon
the work.
The band-saw is a scroll-saw, and operates con-
tinuously. See Band-saw.
Fig. 4768.
Fig. 4770.
Fleetwood's Scrol'-Saw.
2:iy.'r_i/\s s: 'â– oU-Saw.
The example, Fig. 4768 (Fleetwood's), is operated by a treadle
connected by a pitman a, one part of which slides within the
other, rendering it adjustable as to length to the friction-wheel
6, which turns the smaller friction-wheel c and fly-wheel d. A
pitman on the wheel c reciprocates the saw »*, which is con-
nected at each end to guides working in collars fg above and
below the table on which the work is supported. Springs h i
attached to the guides maintain the tension of the saw.
Tapley's is operjited by a treadle a which imparts rotation to
the wheel b and an arm c having rollers at each end The saw
is strained between the bars d e ; the former attached to an
upright wooden spring/. The rotation of the arm r opens out
the endless strnp
g, which ia made
fast below and at-
tached above to the
saw-sash, causing
the downward
stroke of the saw,
which is immedi-
ately thrown up-
w.ird again by the
spring /I The bar
d may he raised or
lowered to suit
paws of different
lengths, and the
throw of the saw
may be varied by
the adjustment of
a buckle on the
strap ^.
Fay's scroll -saw
(Fig 4770) is recip-
rocated by a pit-
man on the wheel
a. The saw-hold-
ers move in verti-
cal guides in the
table-support h and
hanger c, which is
ScroU-fiheel.
SCROLL-WHEEL.
2078
SCUTCHER.
^
»te«died by tension-rods d. Uniform tension is secured at all I Scrutch'er. (Agricullural.) A machine adapted
points of the stroke. j^ break, beat, or scrape flax, etc., to remove woody
Scroll-wheel. The scroll-gear acts upon the | matter. See Scutcher.
pinion, which slides by a feather on the shaft and | Scuf'fle-har'ro'w. (Htisbandry.) A harrow
with cuttiiif,' shares instead of mere teeth.
Fig. 4772. Scuffle-hoe. (Agricultural.) A thrust-hoe
Hljl lllllllimi having the blade in line, or nearly so, with the
' Scuffler. (Agricultural .) A form of culti-
vator used in Britain, and not distinguishable
from the cultivator and scarifiers.
Scull. (Nautical.) a. A short oar rowed
with one hand, two being liandled by a single
man, as in river-wherries and match-boats.
b. An oar used over the stein by a rocking
action obli(]uely against the water.
c. A small boat.
Scull'ing - pro-pel'ler. See Pf.opeller ;
OAIl-I'KOrELLER ; VlBI!ATING-rr.OPELLEU.
Sculp'er. (Eiifirariitg.) See ScunrER.
Sculpt'ure-cop'i-er. An instrument or ma-
chine on the principle of the pantograph, for
copying statuary.
James Watt was working upon a machine for