_HAND AND POWER LOOMS_
[Illustration: FIG. 35.]
The three principal movements in weaving are shedding, picking, and
beating up the weft. By shedding is meant opening the warp threads
to allow the shuttle containing the weft to pass over certain ends
and under others. In the common hand loom the shed is made by the
weaver operating treadles with his feet. Fig. 35 shows the method of
connecting the shafts or staves with the treadles for weaving a plain
cloth. There are two treadles, A and B, placed underneath the loom,
and centred at C. The stave E is connected to the treadle A through
the lever G. The stave F is connected to the same treadle through the
“tumbler” T and the lever M. When the treadle A is pressed down it
will take the stave E down, and the stave F up. For the second pick,
the stave F is connected to the treadle B through the lever H, and the
stave E is connected to the same treadle through the “tumbler” R and
the lever N. Therefore, when the treadle B is pressed down, it will
take the stave F down and stave E up. By alternately pressing first one
treadle and then the other, we get each stave up for one pick and down
for the next, alternately, as required for weaving plain cloth. The
levers M and N are usually called “long lams,” the levers G, H “short
lams,” and the top levers R, T “tumblers.” The cords PP connect the
long lams and tumblers together at the side of the loom.
In mounting this loom for weaving a three-shaft twill, three treadles
are required, one treadle for each pick in the pattern. Supposing one
stave to be down and two up for each pick. The stave required to be
taken down for the first pick must be connected to the first treadle
through a short lam, and the two staves required to be taken up must
be connected to the same treadle through their long lams and tumblers.
Each pick in the pattern must be gone through in this manner. A
separate treadle is required for every pick in the pattern, unless the
same pick is repeated, in which case one treadle will do for more than
one pick. It is not advisable to break the regularity in the order of
treading in order to save a treadle; but in diaper patterns and similar
weaves the effect of a point draft is obtained by reversing the order
of treading.
[Illustration: FIG. 36.]
[Illustration: FIG. 37.]
Figs. 36 and 37 show the design and cording plan respectively for a
twill cloth requiring eight treadles.
[Illustration: FIG. 38.]
The hand loom is practically obsolete in the cotton trade, but it is
still extensively used in silk manufacture, where power looms, as at
present constructed, are not found advantageous for weaving the finer
classes of goods.
The chief shedding motions in power looms are tappets, dobbies, and
jacquards.
There are various kinds of tappets, the simplest and best for plain
or twill weaving being those shown at Figs. 38 and 39. The former is
the more general arrangement. In this the tappets are placed under the
loom, inside the framework. In the arrangement shown at Fig. 39 the
tappets are placed _outside_ the loom, and thus a larger amount of
floor space is taken up by the latter than the former.
Outside tappets are mostly used in the Yorkshire weaving districts, and
are commonly made for weaving with about eight shafts. The top levers,
with “half moons,” are centred at the cross rods EE (Fig. 39), and the
heald is lifted from both sides of the loom. The top levers are very
useful for equalizing the shed, as the connection with the upright rod
can be altered without difficulty.
[Illustration: FIG. 39.]
In a power loom there are two horizontal shafts, the top shaft A (Fig.
38) and the bottom shaft B. The former is used for working the slay,
by means of the crank C, and the connecting rod or “crank arm” D (Fig.
38). The bottom shaft is used for “picking,” and for this purpose it
is necessary that the shaft should revolve at one-half the speed of
the top or crank shaft. The toothed wheel on the bottom shaft must
therefore contain twice the number of teeth in the wheel on the crank
shaft which drives it. As a plain cloth contains two picks to the
round, and the bottom shaft makes one revolution for two picks, the
tappets are fixed to the bottom shaft. Each tappet acts upon treadle
bowl E, and therefore the size of the bowl will require to be taken
into consideration in shaping the tappets. For weaving plain cloth four
staves are usually taken, in order to prevent overcrowding the healds
on each stave, the ends being drawn through the staves in the order 1,
3, 2, 4. As the staves are fastened together in pairs, this is the same
as two staves.
The kind of movement to be given to the staves is very important,
especially in quick-running looms. The staves should be moving quickest
when they are level, and their speed should gradually decrease as the
shed opens. It is obvious that a movement of this kind will put as
little strain as possible on the warp, and therefore cause the fewest
breakages. The depth of the shed should only be sufficient to allow
the shuttle to pass, therefore the “lift” or stroke of the heald is
dependent upon the depth of the shuttle used. The shed when opened
should remain open only long enough to allow the shuttle to pass
through.
_Example._--What lift should a tappet have to make a plain cloth,
the other arrangements in the loom being as follows: Sweep of slay
5½ inches, distance of healds from cloth 8 inches, heald connected
to treadle 24 inches from fulcrum, distance from fulcrum to centre
of treadle bowl 16 inches, size of shuttle 1½ inch broad, 1¼ inch
deep?
Assuming that the tappets are under the loom, as in Fig. 38, the
treadle bowl E is 16 inches from M, and the heald connected 24
inches from M. If slay moves back from cloth 5½″, and the shuttle
is 1½″ broad and 1¼″ deep, it follows that the shed must be 1¼″
deep, or a little over, at a point 4″ from the cloth (5½-1½ = 4).
Then if the heald is 8″ from cloth, the stroke of heald may be
obtained--4: 8 ∷ 1¼: 2½″ stroke of heald, and as 24″ treadle: 16
∷ 2½: 1⅔ lift of tappet required.
To obtain the proper shape of the tappets for a plain cloth, the lift
or stroke of the tappets to give the required lift to the healds must
be obtained. If the lift of the heald is required to be 4 inches, and
the centre of the treadle bowl E (Fig. 38) is situated 12 inches from
the fulcrum of the treadle M, the heald being connected to the treadle
at, say, 18 inches from the fulcrum, the lift or stroke of the tappet
will be obtained as follows:--
As 18 : 12 ∷ 4
4
----
18) 48 ( 2⅔ lift of tappet
36
--
12
In some makes of looms the staves are connected to the treadles at
a point between the fulcrum and the treadle bowl, the fulcrum being
at the front of the loom. This necessitates a larger lift of tappet
than lift of heald. The tappets in this case are very large, and are
preferred by some manufacturers.
[Illustration: FIG. 40.]
=To construct a tappet for a plain cloth from the following
dimensions.=--Lift of tappet, 4 inches. Distance from centre of
shaft to nearest point of contact with treadle bowl, 2 inches; dwell
one-third of a pick. Diameter of treadle bowl, 2 inches.
At a radius of 2 inches describe the circle A (Fig. 40). This circle
represents the distance from the centre of the shaft to the nearest
point of contact with the treadle bowl.
At a radius of 3 inches describe the circle B. One inch added for
radius of treadle bowl.
At a radius of 7 inches describe the circle C. Four inches added for
lift.
The circle B represents the centre of the treadle bowl when the inner
circle of the tappet is acting upon the bowl.
The circle C represents the centre of the bowl when pressed down by the
tappet.
The pattern being a plain one, the circle must be divided into two
equal parts, and each half-circle will then represent one pick. By the
line DE divide the circle into two equal parts. Then, as the healds
must have a pause or dwell equal to one-third pick when at the top and
bottom of their stroke, divide each half-circle into three equal parts
by the lines FK, GH. Divide FH and GK each into six equal parts, and
divide the space between the circles B and C into the same number of
unequal parts, the largest being in the middle, gradually decreasing
towards the circles B and C.
From the corners of these unequal spaces, and with the radius of the
treadle bowl in the compasses, describe circles representing the
position of the treadle bowl at different parts of its movement.
Draw the curved line touching the extremities of the treadle bowl. This
gives the outline of the tappet.
As previously stated, the movement of the heald must be quickest when
the shed is nearly closed, and must gradually decrease in speed as the
shed opens. The unequal spaces into which the lift of the tappet was
divided give this eccentric movement to the heald. The curve of the
tappet will approach nearer to a radial line as the shed closes, and
the heald approaches the centre of its stroke. Referring to Fig. 40, it
will be seen that the treadle bowl is at rest from F to G and from H
to K, or one-third of a pick at both the top and bottom of the stroke.
Therefore the time allowed for change, or for moving the heald from
top to bottom, or _vice versâ_, is equal to two-thirds of a pick. If a
dwell equal to half a pick is required, it can be obtained by dividing
the pick into four equal parts and taking the middle two parts for
dwell. If two-thirds dwell is required, divide the pick into six parts
and take four parts for dwell.
It is usual to give the tappet which operates the back heald a slightly
larger lift than the tappet which operates the front heald. The
difference required can be easily calculated. In looms with the fulcrum
of the treadles at the front, and the healds connected to the treadles
between the fulcrum and the treadle bowls, some of the required extra
lift is obtained by connecting the back heald to the treadle at a
point further from the fulcrum than the front heald is connected. In
looms with the fulcrum of the treadles at the back of the loom, and
the tappets acting between the heald and the fulcrum, there will be a
greater difference between the size of tappets in proportion to the
lift than in the former case.
Tappets for twills, and other simple weaves, having more than two picks
to the round, are usually placed upon a counter-shaft, but outside
tappets are usually worked loose upon the bottom shaft.
The following example will illustrate the principle of constructing
twill tappets:--
Draw a tappet for a 3 up and 1 down twill. Distance from centre of
shaft to nearest point of contact with treadle bowl 3 inches, lift 3
inches, bowl 2 inches diameter, dwell ½ pick.
[Illustration: FIG. 41.]
At a radius of 3 inches describe the circle A (Fig. 41). At a radius of
4 inches describe the circle B (one inch added for treadle bowl). At a
radius of 7 inches describe the circle C (3 inches added for lift).
There being four picks in the pattern, divide the circles into four
equal parts by the lines DE, FG. Then each quarter-circle represents
one pick, and the tappets must be made to make one revolution for four
revolutions of the crank shaft. As the dwell of the heald (when the
shed is open) must be equal to half a pick, or half a revolution of the
crank shaft, divide the first pick into four equal parts by the points
O, L, M; make DP equal to DO, and FN equal to FM, and rule lines from
P, O, M, N to the centre. The distance OM represents the half-pick
dwell, and the distances OP and MN represent the half-pick which will
be allowed for changing the heald from bottom to top of its stroke, and
_vice versâ_. Divide OP and MN into six equal parts, and the lift of
tappet, or the distance between the circles B and C, into six unequal
parts, the largest in the middle and gradually decreasing towards
the two circles. From the corners of the unequal spaces describe the
small circles representing the treadle bowl at different parts of its
stroke, and draw the outline of the tappet touching the extremities of
these circles.
A tappet of this shape acting upon a treadle bowl two inches in
diameter will take the heald down for one pick and allow it to go up
for three picks. The heald will be held stationary for exactly half a
pick when at the bottom of its stroke, and will begin to rise slowly,
and gradually increase in speed as it approaches the centre of its
stroke, and will gradually decrease in speed as it approaches the top
of its stroke. The downward movement will be an exact counterpart of
this. In this kind of tappet it will be noticed that the heald, when it
gets to the top (if it is required up for more than one pick), remains
stationary until it is required to come down. Thus the heald remains at
the top while the circles revolve from N to P.
For this twill there will be four treadles, each treadle being operated
by a tappet of the same shape; but the tappet operating each succeeding
treadle will be placed one quarter of a revolution later than the
previous one.
The size of the treadle bowl has a very appreciable effect upon the
shape of the tappet, more especially when there are several picks to
the round. The movement imparted to the _centre_ of the treadle bowl
will be the exact movement given to the heald as far as regards dwell
and eccentricity, and as the tappet acts on the treadle bowl at a
distance of 1 or 2 inches from the centre, the required amount of dwell
and eccentricity must be given to the centre of the bowl, and the shape
of the tappet obtained accordingly. It will be noticed at Fig. 41, that
to give a dwell of half a pick to the centre of the treadle bowl, a
slightly longer dwell is on the tappet at the inner circle; and as the
size of the treadle bowl increases, this hollowing out of the tappet
must be increased in order to keep the dwell of the heald the same.
Fig. 42 is a drawing of a tappet for a 3 down, 1 up, 1 down, 1 up (six
to the round) twill. Centre of tappet shaft to nearest point of contact
with bowl 4 inches, lift of tappet 2 inches, bowl 1½ inch diameter,
dwell one-third of a pick.
[Illustration: FIG. 42.]
To construct this tappet:--At a radius of 4 inches describe the circle
A. At a radius of 4¾ inches describe the circle B. At a radius of 6¾
inches describe the circle C. As there are six picks to the round,
divide the circles into six equal parts by the lines D, E, F, G, H, I.
As there is one-third pick dwell, divide each pick into three equal
parts, and take the middle one for dwell. Rule the lines L, M, N, O, P,
Q, R, S to the centre, and divide the spaces allowed for change into
six equal parts, and the distance between the circles B and C into
six unequal parts, as in the previous examples. From the corners of
the unequal spaces describe the circles representing the movement of
the treadle bowl, and obtain the shape of the tappet accordingly. It
will be noticed that at point L the treadle bowl begins to dwell, and
remains stationary until it reaches the point S, when it begins to go
up. The heald will thus be down for the first, second, and third picks,
up for the fourth, down for the fifth, and up for the sixth.
[Illustration: FIG. 43.--Woodcroft’s Tappet.]
[Illustration: Fig. 44.
Woodcroft Section Tappet.--Sect. 1, riser (heald-up); sect. 2,
faller (heald-down); sect. 3, left-hand riser; sect. 4, neutral
riser; sect. 5, right-hand riser; sect. 6, left-hand faller; sect.
7, neutral faller; sect. 8, right-hand faller.]
=Woodcroft’s Section Tappets= are much used in weaving heavy
goods, such as velveteens and corduroys. They are made with various
numbers of sections to the round. A single tappet plate of one twelve
picks to the round is given at Fig. 43. Sections are sometimes made in
two kinds only. These are termed “risers” and “fallers,” according as
they raise or depress a heald respectively. Each heald requires one
plate and lever L, and as the tappets revolve, the lever L is moved up
and down. When the lever L is lifted, the heald is moved downwards.
A difference in the character of the shed produced by these tappets
as compared with ordinary tappets will be noticed. When the lever L
is lifted for two or more picks in succession, it comes down about
half-way each pick. This is unavoidable in section tappets consisting
only of “riser” and “faller” sections, which must join together
exactly wherever inserted, thereby causing all the healds to come
towards the centre of the shed after every pick. If there are twelve
sections to the round, any pattern repeating on three, four, six, or
twelve picks may be woven.
It is sometimes considered an objectionable feature of section tappets
(as represented in Fig. 43) that they cause all healds to be brought
level after every pick, thereby producing jerky shedding. This
objection, however, has been overcome by the construction of eight
distinct varieties of sections, as shown in Fig. 44, whereby healds
may remain either up or down for several picks in succession on the
“open-shed” principle, as with ordinary box-plate tappets cast in one
piece.
OSCILLATING TAPPETS.
Another form of shedding device, which embodies certain features of
ordinary rotary tappets and dobbies, is that known as the oscillating
or rocking tappet, an example of which is shown in Fig. 45. This type
of shedding motion consists of a series of plates, B, cast with upper
and lower projecting ridges, C, D, and fulcrumed on shaft A, upon which
they oscillate in a manner indicated by arrows, E. A movement in either
direction represents one pick. On each side of the rocking shaft A, and
oscillating with the tappets, is a pattern chain, F and F′, composed
of bowls and bushes threaded upon spindles, G. Pattern chains, which
represent odd and even picks respectively, are rotated alternately and
intermittently, one spindle for each pick, thereby causing elbow-levers
H to be raised or depressed, according to whether a bowl or a bush is
presented underneath them respectively. The vertical arms of H act upon
loose plates, I (termed “duck-bills”), which are fulcrumed upon short
studs, J. Grooves may thus be formed between either the upper or lower
ridges of tappet plates, and the upper or lower edges of “duck-bills,”
which grooves, by acting upon treadles K, governing healds, will
operate the latter in a manner determined by the pattern chains.
[Illustration: FIG. 45.]
Oscillating tappets are situated at one end of a loom, above the
crank shaft, from which they are driven by wheel gearing and suitable
connecting arms. They are chiefly employed on looms weaving fustians
and similar heavy and strong fabrics.
In plain looms with under tappets, the healds are generally connected
round a top roller or cone, so that when the tappet is pressing one
stave down, it is also taking the other stave up. The shedding is thus
positive. For weaving twills, satins, and such weaves, either spring,
roller, or pulley top motions are used. Where spring tops are used,
the tappet pulls the heald down, and the spring pulls it up again. Of
course, the speed at which the heald moves upward will be controlled by
the shape of the tappet exactly as it is in its downward stroke, but in
the up stroke of the heald, the tappet is only acting negatively. With
roller tops the movement is positive, as the rollers are so constructed
that as one stave is taken down by the tappets another is taken up. If
two staves are taken down, two will be taken up, and the tappets must
be constructed so as to allow this. It is very important also that the
tappets should be of the proper shape, and the exact counterpart of
each other, so that any one stave is allowed to go up at exactly the
same speed, and with the same amount of eccentricity in its movement,
as any other stave which is being taken down by the tappets. Fig. 46
shows the top roller arrangement for plain cloth. Straps are connected
to the staves over the rollers K, K^1; so that when one stave is taken
down by the tappet, the other is taken up.
[Illustration: FIG. 46.]
[Illustration: FIG. 47.]
For three staves the arrangement of rollers as shown at Fig. 47 is
used. The diameter of B must be twice that of A. Sometimes a pulley is
used at C, but when it is a roller, it is fitted into slots at the ends
so as to allow of its being lifted. The diameter of C is immaterial,
but the reason for B and A being as 2: 1 is that when the first heald
is taken down, either the second or third must be taken up the same
distance. Suppose the first stave is pulled down a distance of 4
inches, the strap E, being fastened to the roller A, which is half the
size of B, will be taken up only two inches; and as the tappets are
constructed so as to allow only one heald to go up each pick, if this
heald is the second one, the third being immovable, the second will be
taken up 4 inches, or the same distance that the first was taken down.
If the strap E were fastened to B, the stave would be taken up eight
inches instead of four. This arrangement of rollers is suitable for a 2
and 1 twill; either 2 down and 1 up, or 1 down and 2 up.
[Illustration: FIG. 48.]
[Illustration: FIG. 49.]
For four staves the arrangement shown at Fig. 48 is used. The relative
size of the rollers in this case is immaterial. If the first stave is
pulled down by the tappet 4 inches, and the second is the one allowed
to go up, it will be taken up the same distance. If the first is being
pulled down 4 inches, and the third is the one allowed to go up, the
fourth being immovable, the strap A is pulled down 2 inches, and B
lifted two inches, and the third stave will be lifted 4 inches. If any
one of the four healds is pulled down, another will be lifted the same
distance. This motion can be used for either a 3 and 1 twill or a 2 and
2 twill, or any four-stave pattern with the same number of staves going
up as are going down each pick. The arrangement shown at Fig. 49, in
which the top roller is dispensed with, is sometimes used for a 2 and 2
twill. It will not work a 3 and 1 pattern. The principle of this will
be understood by carefully following the movement of staves in weaving
a 2 and 2 twill. The draft used with Fig. 49 must be 1, 3, 2, 4, or the
first end must be drawn through the first stave, the second end through
the third stave, the third end through the second stave, and the fourth
through the fourth stave. If the pattern is the one shown at Fig. 50,
in which the first and second ends are down for the first pick, it is
obvious that to effect this the first and third staves will be down for
that pick, and the second and fourth staves will be up. For the second
pick the second and third ends are down, and as these are drawn through
the third and second staves respectively, these staves must be down for
the second pick. As the third is already down, it is only necessary to
take the second down, which will pull the first up as required. The
changes in this pattern will be easily understood from the following:--
1st pick: 1st and 3rd staves down, 2nd and 4th staves up.
2nd pick: 3rd and 2nd staves down, 5th and 3rd staves up.
3rd pick: 2nd and 4th staves down, 1st and 3rd staves up.
4th Pick: 4th and 1st staves down, 3rd and 2nd staves up.
[Illustration: FIG. 50.]
[Illustration: FIG. 51.]
Fig. 51 shows a top-roller device for five healds, with bottom heald
staves connected to treadles that are operated by tappets, J, fixed
upon a shaft underneath, but a little in front of the healds, and
driven by a train of wheels from a pinion, B, on the end of the crank
shaft A. This top-roller motion is designed for a five-end weave in
which either one heald only or else four healds, must be raised or
depressed for every pick, uniformly. Therefore, four of the five healds
must be suspended from one pair of rollers C, and one heald from
another pair of rollers D, with both pairs of rollers firmly secured
to the same shaft. Also, in order to obtain the proper leverage that
will ensure the four healds that are suspended from rollers C, exactly
counterbalancing the one heald suspended from rollers D, the diameters
of the pairs of rollers C and D must be in the ratio of one to four,
respectively.
All shedding motions of this type are based on the principle of
equilibrium, whether they are designed as top-roller motions, to
operate above the healds, or as stocks and bowls to operate below
the healds. Therefore, in all top-roller motions, the diameters of
the rollers on the same shaft must always be in inverse ratio to the
number of healds suspended from them. Likewise with stocks and bowls,
the leverage of the stocks must be in inverse ratio to the number
of healds to which the respective ends of the stocks or levers are
connected.
[Illustration: FIG. 52.]
An arrangement for seven staves is given at Fig. 52. The two pulleys
A and B, on the same centre, are in the ratio of 3: 4, and the pulley
D must be twice the diameter of C, the relative size of the remaining
pulleys being immaterial. If the first stave is pulled down, say, 6
inches, and the seventh stave is the one allowed to go up; then the
strap E will be pulled down 2 inches, and the strap F taken up 1½
inches, the strap G 3 inches, and the stave 6 inches, which is the same
distance that the other stave was pulled down. It will be the same with
any other healds in the set. If one stave is taken down, any other one
left loose by the tappet will be taken up the same distance. Instead of
the pulleys A and B, a lever may be used with its two arms in the ratio
of 3 to 4, the four staves being connected to the shorter arm, and the
three staves to the longer arm.
In some looms the positions of tappets and roller heald-motions are
inverted: tappets being fixed above, and roller motions below, healds.
In such cases the roller motions are known as “stocks and bowls,” which
terms, however, more correctly describe those devices consisting of a
combination of levers and bowls, or rollers, and not those consisting
of rollers upon shafts. In either case, they are based upon the same
principle of leverage, and act in an exactly similar manner to each
other. These devices are very limited in their scope, as regards
variety of weaves for which they are suitable, and may only be employed
for weaves of a regular character, in which the number of healds up
and down is the same for every pick. Of course, any number of healds
in a set may be up or down as required, but when once that number is
selected, and healds are tied up accordingly, it may not be changed
without re-tieing up.
[Illustration: FIG. 53.]
Fig. 53 shows a front and end elevation of what is known as the
Yorkshire shedding motion, in which tappets are cast upon a sleeve
slid upon one end of the second motion or picking shaft D, to operate
treadles, M, fulcrumed at N. Connecting rods, J, connect treadles,
M, with quadrant jacks, O, secured to cross-bars, K. These serve as
fulcra for the jacks, which are connected to upper heald staves, P, by
means of straps and cords, R, whilst bottom heald staves are attached
by cords to springs, S, for the purpose of pulling healds down, after
being raised by the tappets.
PICKING.
As soon as a warp-shed is sufficiently opened by the healds, the
shuttle, containing weft, is propelled through it. That operation is
termed “picking,” and may be accomplished by either of two types
of picking motions known as “over” and “under” picking motions. The
“over-pick,” also known as the “cone” and Blackburn pick (Fig. 54),
is in most general use, especially for narrow and quick-running looms
weaving light and medium-weight fabrics; whilst the “under-pick” (Figs.
56 and 57), of which there are many modifications, is chiefly confined
to medium and broad looms, which require a picking motion capable of
developing greater force. A shuttle is propelled by a picker made of
hide, which is connected by means of a leather strap to the picking
stick A (Fig. 54). The upright shaft B is the fulcrum of the lever.
The cone C is the short arm of the lever which receives the force from
the picking tappet D. The tappet is so shaped that as it revolves it
gives a sudden quick movement to the cone-shaped stud, and therefore to
the shuttle. It is obvious that as the shuttle must move from one side
of the loom to the other, and back again, for two revolutions of the
crank shaft, the picking tappets must be placed on a shaft whose speed
is one-half that of the crank shaft; therefore the bottom shaft in the
loom on this account is made to move at the required speed, and the
picking tappets are placed on this shaft at opposite sides of the loom.
[Illustration: FIG. 54.]
The chief requirement in a good pick is that as little force as
possible shall be wasted in the loom. The relative positions of the
tappet shaft and cone should be such that the force is exerted as
nearly as possible in the direction of the dotted line E at right
angles with the upright shaft B. It is impossible to effect this
throughout the whole course of the stroke, but it is obvious that if
this is approached as nearly as possible, the pick will be smooth, and
the wear and tear reduced to a minimum. A very considerable amount of
power is wasted if the direction of the force is too much downward.
The direction of the force is at right angles to a line drawn tangent
from the cone at the point of connection with the picking tappet. Thus
in Fig. 54 the direction of the force is indicated by the dotted line
M, which is at right angles to the dotted line N, drawn tangent to the
cone at the point of connection with the tappet.
[Illustration: FIG. 55.]
The intensity of the force depends on the length of the stroke of the
tappet and on the suddenness of the curve of the working face. If in
two looms the length of tappet is the same, but in one the portion of
a revolution occupied in making the stroke is less than in the other,
there will be a greater intensity of force in the loom with the quicker
stroke. In Fig. 55 the portion of a revolution occupied in making the
stroke is indicated by the angle AB. If this angle is increased, the
force of the pick will be lessened, and if the angle be decreased, the
force of the pick will be augmented. It will be understood from this
that if the picking tappets are short the pick is liable to be harsh.
If a fair length of tappet is given, a smoother and better-timed pick
can be made. The curve on the picking tappet gradually approaches
a radial line as it nears the end of the stroke, but the combined
influence of the change in the position of the cone and the backward
movement of the slay causes the shuttle to move quickest in the early
part of its movement in the box.
There is a relation between the length of the shuttle-box and the
length of the picking tappet. If the tappet is a short one, the
shuttle-box must be short; and if a longer tappet is used--the leverage
of the picking arm and other parts being the same--the shuttle-box will
be longer.
It is obviously inadvisable to have too short a tappet, as the movement
of the shuttle in the box must in that case be extremely sudden, in
order to have the necessary force.
[Illustration: FIG. 56.]
[Illustration: FIG. 57.]
An underpick motion is given at Fig. 56. A picking treadle, A, centred
at C, is pressed suddenly down by the picking bowl B, which is fastened
on to the wheel on the bottom shaft in the loom. A strap, E, connects
the treadle and the picking lever. In Fig. 57 this connection is shown.
The strap from the treadle is fastened to the quadrant, and as the
treadle is pressed suddenly down, the picking lever H is moved forward.
The shape of the curve E, which the picking bowl strikes, regulates
the character of the movement given to the lever H, and it is well
not to have the curve too small and sudden, or the pick will not be
satisfactory. The curve on the treadle in Fig. 88 (p. 120) is perhaps
better than the one in Fig. 56, as it is longer, and is therefore not
liable to be so jerky.
There are numerous other picking motions, which chiefly differ in the
mechanism for actuating the picking lever.
=Beating up the Weft= is the third primary movement in weaving.
This movement is performed by a crank on the top shaft in the loom and
a connecting rod or crank-arm which connects the crank and the slay
together. This is shown at Fig. 38, where the crank C and crank-arm
D give a reciprocating movement to the slay S. The slay moves upon a
rocking shaft, E, as a fulcrum, and when the crank is at the front
centre the slay-swords should be perpendicular, or nearly so. Sometimes
the fulcrum is taken a little forward, but it is never advisable to
have the slay over the perpendicular when in contact with the cloth.
The movement of the slay should be eccentric. It is obvious that
when the slay is at the back of its stroke its movement should be
sufficiently slow to allow time for the shuttle to pass through
the shed; and that when beating up, the speed of the slay should
be sufficient to knock the weft firmly into the cloth. A crank and
crank-arm give the kind of movement required.
The eccentricity of the slay’s movement depends upon the length of
the crank and crank-arm, and upon the position of the crank-shaft in
relation to the point of connection of the crank-arm with the slay. The
position of the crank-shaft in relation to the connecting pin varies in
different makes and widths of looms. We shall see that the position of
the shaft and the direction in which the loom runs have an important
bearing on the force exerted by the slay in beating up the weft. For
ordinary looms the usual position of the shaft is a little below the
level of the connecting pin when at the front centre, and when the
shaft is in this position the movement of the slay is the most even
and least eccentric. To obtain this position of the crank-shaft in a
diagram, first draw the line SA (Fig. 58) to represent the slay-sword
when the reed is in contact with the cloth; this we will assume is
perpendicular. We will suppose SA to be 24 inches, S being the rocking
shaft and A the connecting pin which connects the crank-arm with the
slay. Suppose the loom we are dealing with to have a 3-inch crank and a
12-inch crank-arm. Describe the arc AN from the centre S, and mark off
on the arc a distance from A equal to twice the length of the crank. As
the crank is 3 inches long, mark off the point B, 6 inches from A. This
point B represents the position of the connecting pin when the slay is
at the back of its stroke.
[Illustration: FIG. 58.]
From A, rule the line AX in such a position that the arc AB makes
the least possible departure from it. It will be found that this
necessitates AX cutting the arc AB at a point a little past the middle
of the arc. With the length of the crank and crank-arm, viz. 15 inches,
in the compasses, from A as the centre cut the line AX at E, and this
gives the position for the crank-shaft which will give the least
possible eccentricity to the slay. This will be obvious, as the nearer
the connecting pin moves on the straight line AX, the less will be the
eccentricity of the slay.
That the movement of the slay in the back half of its stroke is slower
than in the front half can easily be proved by taking the length of the
crank-arm in the compasses, and, after bisecting the arc AB at C, from
C marking off the points D and H on the crank circle. It will be seen
that both these points are somewhat inside the top and bottom centres
of the crank indicated by the dotted line, and therefore the slay moves
from C to A and back, the front half of its stroke, in less time than
it moves from C to B and back to C. The reason for this eccentricity or
unevenness in the movement of the slay is that when the crank is moving
from the back centre to the top centre the crank-arm is oscillating
and opening an angle with AX while the slay is moving forward, and
therefore while the crank is making this quarter of a revolution, the
connecting pin of the slay will move something less than from B to C;
and while the crank is moving from the top centre to the front centre,
the crank-arm is straightening or closing the angle while the slay
is moving forward, and thus the connecting pin will move a greater
distance than from C to A while the crank is making this quarter of a
revolution. When the crank moves from front to bottom centre the angle
is opening while the slay is moving backwards, and therefore the pin
will move a little more than from A to C; and when the crank moves
from bottom to back centre the angle is closing while the slay moves
backwards, thus retarding the velocity of the slay.
[Illustration: FIG. 59.]
This will be better understood from Fig. 59, where CD is the
crank-arm, and ED the crank at the top centre. A is the position of
the connecting pin when at the front of its stroke, and B its position
when at the back of its stroke. The dimensions are as in Fig. 58--viz.
12-inch arm, 3-inch crank--and for simplicity we will assume the
connecting pin moves on the straight line AE. From A to B is 6 inches,
and therefore it is obvious that AC is something over 3 inches, and
that the connecting pin moves this distance whilst the crank is making
the quarter of a revolution from top to front centre. The distance AC
can be obtained as follows. It is obvious that CDE is a right-handed
triangle, and therefore CD^2 is equal to CE^2 + ED^2. Therefore
CD^2-ED^2 = CE^2, and having obtained the length of CE, we can subtract
this from AE, which leaves the length of AC. The formula will stand
thus--
CD^2 - ED^2 = CE^2
12^2 - 3^2
144 - 9
∴ 135 = CE^2
and CE = √(135) or 11·6189
length of AE = 15·0000 inches
11·6189 inches
-------
AC = 3·3811 inches
The answer may be obtained in one calculation as follows:--
AE - √(CD^2 - ED^2) = AC
or 15 - √(12^2 - 3^2)
15 - √(144 - 9)
15 - √(135)
15 - 11·6189 = 3·3811
We thus see that the connecting pin moves 3 inches + 0·3811 inch while
the crank is moving from the top to front centre. It will also move the
same distance while the crank moves from front to bottom centre.
When the crank is moving from the bottom to the back centre, the
connecting pin will move 3 inches - 0·3811.
3·0000
0·3811
------
2·6189 inches,
and the same distance when the crank moves from back to top centre.
It is often necessary in comparing looms to obtain the distance
travelled by the connecting pin for a smaller movement of the crank
than a quarter of a revolution.
Suppose it is desired to find the distance travelled by the connecting
pin while the crank moves through 30 degrees to the front centre.
Take a 4-inch crank and 12-inch crank-arm. In Fig. 60, ED is the crank,
4 inches, and DC the crank-arm, 12 inches, the angle O = 30 degrees. P
is the position of the connecting pin when at front of its stroke.
[Illustration: FIG. 60.]
To find the distance CP. From a table of natural sines we can obtain
the sine of an angle of 30 degrees, viz, sin 30° = 0·5, and therefore,
knowing the length of ED, viz. 4 inches, we can obtain the length of
DN, it being 0·5, or half of ED, in an angle of 30 degrees.
Having two sides of a triangle, we can obtain the third side thus:
ED^2 - DN^2 = EN^2 and
CD^2 - DN^2 = CN^2
Having obtained the length of CN and EN, we can easily obtain CP by
subtracting CF from the length of crank and crank-arm together. Working
out the problem in figures we get--
ED^2 - DN^2 = EN^2
4^2 - 2^2 = EN^2
16 - 4 = EN^2
12 = EN^2
∴ EN = √(12) or 3·4641. And
CD^2 - DN^2 = CN^2
12^2 - 2^2 = CN^2
144 - 4 = CN^2
140 = CN^2
∴ CN = √(140) or 11·8321
and 11·8321 + 3·4641 = 15·2962
Therefore CE = 15·2962 inches, and subtracting this from PE, which is
16 inches (12 + 4 = 16), we get 16-15·2962 = 0·7038 as the distance CP,
which is the distance moved by the connecting pin for the 30 degrees
movement of the crank.
The complete formula is as follows:--
PE-[√[(ED^2-DN^2)] + √[(DC^2-DN^2)]] = CP, or distance moved by the
connecting pin for the given number of degrees through which the crank
moves, ND being obtained from a table of sines.
To find the distance moved by the connecting pin while the crank moves
through 5 degrees--say, from 30 degrees to 25 degrees in beating up.
To solve this it will only be necessary to subtract the length of CE
when the crank is forming an angle of 30 degrees from the length of CE
when the crank forms an angle of 25 degrees. In the previous example
we found that for 30 degrees, CE = 15·2962 inches, and therefore
proceeding in the same manner for 25 degrees, we get from table of
sines, sin 25° = 0·4226, and 0·4226 of 4 inches 1·69; therefore ND
=1·69 inches, and
4^2 - 1·69^2 = EN^2
16 - 2·856 = EN^2
13·144 = EN^2
∴ EN = √(13·144) or 3·626
and 12^2 - 1·69^2 = CN^2
∴ 144 - 2·856 = CN^2
141·144 = CN^2
∴ CN = √(141·144) = 11·88;
therefore CN = 11·88 inches, and CE will equal 11·88 + 2·626, or 15·506
inches, when the crank is forming an angle of 25 degrees.
15·506 length of CE for 25 degrees
15·296 length of CE for 30 degrees
------
inches 0·210 distance moved by pin whilst crank moves
through 5 degrees, from 30 degrees to 25
degrees, in beating up.
In this manner it is easy to calculate the distance travelled by the
pin for any number of degrees moved by the crank, and by comparing the
velocity of the slay in different looms, the force of the beat up can
be compared.
_The force exerted by the slay varies as the square of its velocity._
Thus, if in two looms where the _weight_ of the two slays and the
tension on the two warps are the same, the velocity of the slay in one
loom is twice that of the other at a certain point in the beat up, the
force of the former slay at that particular point will be four times
the force of the latter, 1^2: 2^2 ∷ 1: 4.
We can thus compare the force exerted by the slay in different looms at
any point of the beat up.
The force of the beat up is chiefly exerted upon the pick when the
crank is nearly at the front centre, and the force exerted will also
depend considerably upon the tension on the warp; but the slay is doing
some work in beating up from the moment the reed begins to move the
pick forward.
Possibly the most reliable method of comparing the force of the beat
up in different looms is to calculate the time occupied by the slay
in moving through a specified distance at the front of its stroke in
beating up. This necessitates a rather different calculation to the
preceding examples, but is equally as simple.
[Illustration: FIG. 61.]
Suppose it is required to compare the force exerted by the slay in
beating up (say the front 1 inch of its stroke) in two looms, one with
a 12-inch crank-arm and 3-inch crank and the other with an 11-inch arm
and 4-inch crank. The weight of the slays, the speed of the looms, the
tension on the warps, and the timing of the primary movements, the same
in each case.
In Fig. 61 the smaller circle represents the 3-inch crank and the
larger one the 4-inch crank. CP = 1-inch, CB = 11-inch arm, and CD =
the 12-inch arm. It is obvious that if we can obtain the two angles
made by the cranks, viz. ∠ CAB and ∠ CAD, we shall be able to get the
time, or fraction of a revolution, occupied in moving the slay from
C to P. As we know the three sides of the triangle we can obtain the
angle enclosed by any two sides, and what is required in this case is
to obtain the angles BAC and DAC. In triangles of this kind where there
is no right angle, we can obtain the cosine of the angle as follows:--
CA^2 + AD^2 - DC^2
------------------ = AQ, the cosine of angle DAC,
2CA.AD
and CA^2 + AB^2 - BC^2
------------------ = AN, the cosine of angle BAC.
2CA.AB
The proof of this formula is given in Euclid, Book 2.
Having obtained the cosines of the two angles, we can find the angles
themselves by referring to a table of sines and cosines.
Then as AP = 15 inches,
CA = 14, AD 3 inches, DC 12 inches, BA 4 inches, BC 11 inches; and
reducing the formulæ to figures, we get:
14^2 + 3^2 - 12^2 196 + 16 - 144
----------------- = -------------- = 0·7262 cosine,
2 × (14 × 3) 84
and by referring to a table of sines, we find that cosine 0·7262 =
angle 43° 26´, therefore angle DAC = 43½°, about. Also
14^2 + 4^2 - 11^2 196 + 16 - 121 91
----------------- = -------------- = --- = 0·8125,
2 × (14 × 3) 112 112
and by referring to a table of sines and cosines, we find cosine 0·8125
= angle 35⅔°.
We thus find that to move the connecting pin 1 inch to the front of
the stroke, in the loom with 11-inch arm, the 4-inch crank will move
through 35⅔°, and in the loom with the 12-inch arm the 3-inch crank
will move through 43½° for the same movement of the slay. Assuming
the force exerted by the latter to be 1, the force of the former will
be as 35⅔ squared: 43½ squared ∷ 1: _Ans._
It may be as well here to give a short explanation of the system of
obtaining angles by sines and cosines.
As the crank moves forward it is obvious that the line DQ will become
shorter, and as the angle becomes larger the line DQ will increase in
length. In trigonometry, the ratio between the length of the line DQ
and the radius AD is called the _sine_ of the angle, and if the radius
is 1, the length of DQ will be the value of the sine. In an angle of
30° the sine is exactly ½ the radius, and the relation between the
radius and the sine for every angle is known, and arranged in “tables
of sines.” The length of AQ will also vary with the angle, and the
length of this line is called the “cosine” of the angle QAD. The
_cosine_ of an angle of 30° is therefore the same as the _sine_ of an
angle of 60°. When the sine is known it is easy to obtain the cosine as
follows:--
Cosine = √(1-sin^2). Thus for an angle of 30°, cosine = √(1-0·5^2), or
cos^2 = 1-0·5^2, therefore cos^2 = 1-0·25, or cos^2 = 0·75, ∴ cos =
√0·75 = 0·866. By reversing, the sine may be obtained from the cosine.
The value given to the sines and cosines must not be taken for the
_actual_ length of the lines; they are simply the ratio to the radius.
Thus in an angle of 30°, if the radius is 1 inch the length of the sine
will be ½ inch and the cosine 0·866 inch. If the radius is 2 inches,
the actual length of the sine will be 1 inch and of the cosine 1·732
inches.
TABLE OF SINES AND COSINES.
+--------+--------+--------+------+
|=Angle.=| Sine. | Cosine.|Angle.|
+--------+--------+--------+------+
| =0°= |=0·00= |=1·00= | =90°=|
| 1° | ·0175 | ·9998 | 89° |
| 2° | ·0349 | ·9994 | 88° |
| 3° | ·0523 | ·9986 | 87° |
| 4° | ·0698 | ·9976 | 86° |
| =5°= | =·0872=| =·9962=| =85°=|
| 6° | ·1045 | ·9945 | 84° |
| 7° | ·1219 | ·9925 | 83° |
| 8° | ·1392 | ·9903 | 82° |
| 9° | ·1564 | ·9877 | 81° |
| =10°= | =·1736=| =·9848=| =80°=|
| 11° | ·1908 | ·9816 | 79° |
| 12° | ·2079 | ·9781 | 78° |
| 13° | ·2250 | ·9744 | 77° |
| 14° | ·2419 | ·9703 | 76° |
| =15°= | =·2588=| =·9659=| =75°=|
| 16° | ·2756 | ·9613 | 74° |
| 17° | ·2924 | ·9563 | 73° |
| 18° | ·3090 | ·9511 | 72° |
| 19° | ·3256 | ·9455 | 71° |
| =20°= | =·3420=| =·9397=| =70°=|
| 21° | ·3584 | ·9336 | 69° |
| 22° | ·3746 | ·9272 | 68° |
| 23° | ·3907 | ·9205 | 67° |
| 24° | ·4067 | ·9135 | 66° |
| =25°= | =·4226=| =·9063=| =65°=|
| 26° | ·4384 | ·8988 | 64° |
| 27° | ·4540 | ·8910 | 63° |
| 28° | ·4695 | ·8829 | 62° |
| 29° | ·4848 | ·8746 | 61° |
| =30°= | =·5000=| =·8660=| =60°=|
| 31° | ·5150 | ·8572 | 59° |
| 32° | ·5299 | ·8480 | 58° |
| 33° | ·5446 | ·8387 | 57° |
| 34° | ·5592 | ·8290 | 56° |
| =35°= | =·5736=| =·8192=| =55°=|
| 36° | ·5878 | ·8090 | 54° |
| 37° | ·6018 | ·7986 | 53° |
| 38° | ·6157 | ·7880 | 52° |
| 39° | ·6293 | ·7771 | 51° |
| =40°= | =·6428=| =·7660=| =50°=|
| 41° | ·6561 | ·7547 | 49° |
| 42° | ·6691 | ·7431 | 48° |
| 43° | ·6820 | ·7314 | 47° |
| 44° | ·6947 | ·7193 | 46° |
| =45°= | =·7071=| =·7071=| =45°=|
| Angle | Cosine | Sine | Angle|
+--------+--------+--------+------+
We see from Fig. 61 that in a loom with a 4-inch crank and 11-inch arm,
the velocity of the slay is much greater when beating up than with the
3-inch crank and 12-inch arm.
The effect of the length of the crank-arm on the velocity of the slay
can easily be shown by a diagram or by calculation. If the length of
the crank-arm be altered without altering the length of the crank,
there will be found a somewhat quicker movement of the slay at the
beat up in the loom with the shorter arm. The difference is not so
great when the crank-arm is a long one in proportion to the crank. The
chief cause of the difference in the velocity of C in Fig. 61 is the
difference in the length of the _crank_. It is obvious that the longer
the crank the greater the angle which it will cause the arm to make,
and therefore the greater will be the acceleration of the velocity of C
when the angle is closing and the slay moving forward. Likewise, it is
obvious that the shorter the arm the larger will be the angle to close,
but the _principal_ thing to notice is that an increase in the length
of the _crank_ causes an increase in the velocity of the slay _owing
to the extra distance which it has to travel in each revolution_; so
that even if the crank-arm were lengthened in exact proportion to the
increase in the length of the crank, so as to keep the angle to be
closed in beating up the same, there would still be a considerable
increase in the velocity of the slay, caused by the extra distance it
has to travel. This lengthening of the crank has obviously much more to
do with the increase in velocity of the slay than the shortening of the
arm has.
The longer the crank the further back from the cloth will the slay be
taken, and assuming that the shed is open for the shuttle when the
crank is at the bottom centre, a long crank is obviously more suitable
for a wide loom, as, having to move further back, it will allow a
longer time for the shuttle to pass through the shed than a short crank
would; therefore the wider the loom, the longer the crank is required
to be to allow time for the shuttle to pass.
The time allowed for the passage of the shuttle may also be increased
by using a short arm so as to increase the eccentricity of the slay.
The longer the crank, the greater the velocity of the slay, therefore
a long crank is suitable for _heavy_ work, as it stores up more force
in the slay than a short one. The force may also be increased by
shortening the crank-arm, thus increasing the eccentricity of the slay.
[Illustration: FIG. 62.]
The position of the crank-shaft in relation to the connecting pin
has some effect upon the _eccentricity_ of the slay’s movement. Fig.
62 shows this, but to see clearly the effect it would be advisable
to make an accurate drawing to a large scale. Four positions of the
crank-shaft are shown. The one on the line A is just a little below
the level of the connecting pin, so that the pin moves as nearly as
possible on the line A when making the front quarter of its stroke.
The circle on the line B is the position where the pin moves as nearly
as possible on line B when at the back quarter of its stroke; D is any
higher plane, and C any lower one. Divide the stroke of the connecting
pin LR into four equal parts, and from S, with the crank-arm in the
compasses, cut the circles with the arc E, and from T cut the circles
with the arc F. It will be found that in the circle A, OP is slightly
longer than in any of the other circles; therefore this is the position
where the beat up is slowest. It will also be found that in the circles
B and C there is scarcely any difference in OP, therefore sinking the
crank-shaft from within reasonable limits makes very little difference;
if anything, there is a slight decrease in the size of OP as the plane
is lowered, but it is very slight, and the increase in the velocity
of slay would also be very slight. On the other hand, by raising the
crank-shaft to D a considerable increase in the velocity of the slay in
beating up takes place, as it will be found that in this circle OP is
much less than in the others.
At the back of the stroke it will be found that in the plane B the
distance XY is least; therefore there is here the least dwell of the
slay at the back of its stroke with the shaft in this position. This
is because the pin moves as nearly as possible on the line B whilst
the crank is at the back part of its stroke. As the crank is raised or
lowered the dwell at the back increases slightly.
Reversing the direction of the loom makes a difference in the beat-up.
It will be found that in the circle A, OP and ON are about equal,
therefore there will be scarcely any change in the velocity of beat-up
by reversing the loom; but as the shaft is lowered ON will be found to
become less than OP, and therefore a quicker blow is given by reversing
the loom if the shaft is in this position. If the shaft is raised, as
in the case of circle D, it will be found that ON becomes _greater_
than OP; therefore with the crank above A, reversing the direction of
the loom will cause a slower and weaker beat-up.
In the diagram, Fig. 62, the crank and crank-arm are the same length
for each position, the centre of the shaft being indicated by the
dotted arc.
_Timing of the Primary Movements._
[Illustration: FIG. 63.]
The primary movements, shedding, picking, and beating up, are timed
differently in relation to each other in weaving different classes
of fabrics. For plain cloths, or other cloths where a good cover is
required--that is, where the warp has to be spread--the crank should be
set about the top centre when the healds are crossing each other. At
Fig. 38 the loom is timed in this manner. When so timed it is obvious
that the shed will be considerably or altogether open when the reed is
in contact with the cloth. By sinking the centres of the healds below
a line drawn from the temple to the back rest, the upper portion of the
shed is always slack, and if the pick is beaten up in a crossed shed,
the loose ends of the warp are spread between the taut ones. In Fig.
63 the straight line AB is drawn from the front carrier A to the back
carrier B. The centres of the healds when level are on the line ACB,
the point C being a little way below the line AB. When one stave is
lifted a certain distance and the other goes down the same distance, it
is obvious that the upper portion of the warp will be slacker than the
lower portion, because the line ADEFB is shorter than ADGFB, and when
the reed beats up with the warp in this position the slack ends are
spread between the taut ones, thus giving a good cover to the cloth and
preventing the reed marks from showing. Each set of ends alternately
becomes slack.
Another advantage of beating up when the shed is crossed or partly
open for the succeeding pick is that the pick is held more firmly in
position than when the shed is not crossed, and therefore the picks can
be got in better.
In twilled cloths the boldness of the twill is somewhat affected by
the warp being spread, and these cloths are often preferred when made
without the healds having been sunk.
[Illustration: FIG. 64.]
If the dwell on the tappet is equal to one-third of a pick, as in Fig.
64, the line D will mark the point of the tappet when the crank is at
the top centre. When the crank has made one quarter of a revolution and
is at the front centre with the reed in contact with the cloth, the
point E will be acting on the treadle bowl. It will be seen that here
the shed is almost fully open. When the crank is at the bottom centre
the point G will be acting on the bowl, and the shuttle should just
be entering the shed. When the point H of the tappet is acting on the
bowl the shed will be commencing to close, and the shuttle must be just
leaving the shed. When the point I is acting on the bowl the crank will
be at the back centre, and when the crank reaches the top centre the
healds will be again level.
If the dwell on the tappet is more than one-third pick, and at the
commencement the crank is set on the top centre with the healds level,
the shed will keep open longer for the shuttle to pass through, and
would be more open when the crank reached the front centre. It will
be obvious that for a wide loom a longer dwell is required than for a
narrow loom.
By having the shed fully open before the shuttle enters the shed, the
warp is spread and a good cover put on the cloth, but all this dwell
is taken off the time which would otherwise be allowed for opening and
closing the shed, and therefore means extra strain on the warp.
If it is not necessary to spread the warp, the shed need not be fully
open until the shuttle is entering the shed. In this case the greatest
possible amount of time is allowed for opening and closing the shed,
thus putting as little strain as possible on the warp.
_Speed of Tappets._
As previously stated, the bottom shaft in the loom, being the one used
for picking, revolves at one-half the speed of the crank-shaft, and
therefore plain cloth tappets may be fastened on the bottom shaft.
Tappets of more than two picks to the round are usually fixed on a
counter-shaft, S (Fig. 65), in looms with inside tappets. Sometimes
the wheel E is geared directly into the wheel C on the bottom shaft,
but usually a carrier-wheel, D, is used to convey the motion from the
bottom shaft. The number of teeth in the carrier wheel has no effect
on the speed of the tappets, as it is used simply to fill up the space
between the bottom and counter-shafts.
[Illustration: FIG. 65.]
If the wheel on the crank-shaft A contains 45 teeth, and the wheel B 90
teeth, C 40 teeth, and E 60 teeth, the tappet-shaft S will be making
one revolution for three revolutions of the crank-shaft; therefore
these wheels will do for three-end twill tappets. This may be proved by
multiplying the drivers together and the drivens together, and dividing
one by the other, thus--
(90 × 60)
--------- = 3
(45 × 40)
It is usual to place two or three wheels on the bottom shaft of the
loom, so that any one of them may be geared into the carrier wheel D,
each giving the required speed for different tappets. If a 40 wheel,
a 30 wheel, and a 24 wheel are placed on the bottom shaft in such a
manner that they can be moved along the shaft and any one of them be
geared into the carrier wheel, any 3, 4, or 5 pick tappets can be
driven with these wheels. We have seen that a 40 wheel at C gives three
picks to the round.
Suppose the 30 wheel at C is geared into the carrier wheel, we get--
(drivens 90 × 60)
----------------- = 4,
(drivers 45 × 30)
or the relative speed of the tappets and crank-shaft are as 1:4;
therefore these wheels may be used for any tappets with four picks to
the round.
If the 24 wheel is at C, we get:
drivens 90 × 60
------- = 5,
drivers 45 × 24
and thus we get the proper rate of speed for tappets five pick to the
round.
Some loom makers use the wheel E as a change wheel. With a 24 wheel C
and a 36 wheel E we get three picks to the round, thus--
drivens 90 × 36
------- = 3
drivers 45 × 24
With a 24 wheel C, a 48 wheel E gives 4 picks,
With a 24 wheel C, a 60 wheel E gives 5 picks,
With a 24 wheel C, a 72 wheel E gives 6 picks.
_Example._--Find the number of teeth for the wheel C on the bottom
shaft to drive tappets seven picks to the round, wheel on tappets
63 teeth.
90 × 63
------- = 18 wheel. _Ans._
45 × 7
Woodcroft’s tappets, as a rule, are driven directly from the
crank-shaft. As these tappets are usually of a large circumference,
a large wheel on them is of no disadvantage, although sometimes
intermediate wheels are used.
If the tappets are twelve to the round, and the wheel on the tappets
contains 192 teeth, a driving wheel of 16 teeth will be required on the
crank-shaft.
192
--- = 12 picks to the round
16
For driving outside tappets, as in Fig. 39, a driving wheel on the
crank-shaft and two intermediate wheels are generally used. The
tappets are placed on the bottom shaft outside the loom, but they are
loose upon the shaft, and can, of course, be made to revolve at a
different speed to the shaft, either in the same or in the opposite
direction. This system of driving the tappets is shown at Fig. 66. The
wheel A, on the crank-shaft, drives the wheel B, on an intermediate
stud; the wheel C, on the same centre, drives the tappet wheel D.
[Illustration: FIG. 66.]
To find the wheel on the crank-shaft, or the first driver, the other
wheels being as follows: first driven wheel, B, 36 teeth; second
driver, C, 12 teeth; tappet wheel, D, 120 teeth.
Multiply the two driven wheels together, and divide by the given driver
multiplied by the picks to the round, thus--
36 × 120
-------- = 40 first driver, A.
12 × 9
To find the second driver for eight picks, the other wheels being:
first driver, A, 20; first driven, B, 40; second driven, D, 60.
The given driver multiplied by the picks to the round, 20 × 8 = 160;
the drivens multiplied together, 40 × 60 = 2400; 2400 ÷ 160 = 15 wheel
required.
To find either of the driven wheels, multiply the two drivers and the
picks together, and divide by the driven given wheel, thus--
_Example._--Find the wheel for the tappets, D, for 10 picks to
the round, the other wheels being: first driver, 16 teeth; first
driven, 32 teeth; second driver, 20 teeth.
16 × 20 × 10
------------ = 100 wheel required
32
To find both intermediate wheels, multiply the given driver by the
picks to the round, and as the product is to the teeth in the tappet
wheel, so is the required driven to the required driver.
_Example._--Find the two intermediates for 10-pick tappets, if the
wheel on the crank-shaft has 18 teeth, and the wheel on the tappets
120 teeth. The 18 × 10 = 180, and therefore the two required
wheels must be in the proportion of 180 to 120, the former being
the driven wheel. Thus a 36 driven and a 24 driver will give the
required speed to the tappets. That this is correct may be seen
from the following:--
18 × 24
-------- = 10 picks
36 × 120
That the required wheels must be in this proportion will be apparent
from the fact that if the wheel B has ten times the number of teeth in
A, then B is revolving at the speed at which the tappets are to move;
therefore if the wheel C has the same number of teeth that D has, the
speed of the tappets will remain the same.
FAST-AND LOOSE-REED LOOMS.
One of the most important motions in the power loom is that by which
the loom is stopped automatically when the shuttle is caught in the
shed or for some reason does not enter the shuttle-box. A motion of
this kind has always been considered necessary since the introduction
of the power loom. If the shuttle be caught in the shed as the reed is
beating up, it is obvious that great damage to the warp must result
unless the loom is brought to a sudden stop or the reed thrown out.
The oldest form of protector is the “stop rod.” In this the reed is
fast, and if the shuttle is caught in the shed or flies out, the loom
is brought to a sudden stop before beating up. Fig. 67 will illustrate
the principle of this motion. If the shuttle enters the box safely it
presses back the swell S, which projects inside the box and is held
there by a spring. As the swell is pressed back it raises the lever B
above the frog F as the slay beats up. If the shuttle for any reason
does not enter the box, the swell is not pressed back, and as the slay
moves forward in beating up, the lever B catches the frog F, which
is moved a little and applies the brake G, and also knocks off the
loom handle H, which removes the belt on to the loose pulley. Before
the application of the brake to this motion the frog was fixed to
the framework of the loom, and it will easily be understood that the
concussion caused many breakages. A stop rod protector was patented in
1791, but the brake was not applied until 1840 or thereabouts.
[Illustration: FIG. 67.]
The loose reed is a better way of preventing damage to the warp by the
shuttle being caught. If the shuttle is caught in the shed it throws
out the reed and stops the loom. Its action will be understood from
Fig. 68. A rod, C, runs underneath the shuttle-race at the back of the
slay, and the finger B is fastened to it. The reed is held in position
by a board, A, which is also connected to the rod C, as shown in the
diagram. If the shuttle is caught in the shed, it presses back the reed
and the board A, and lifts the finger B to the upper side of the frog
F, and as the slay moves forward it throws the board A further back and
the reed out at the bottom, and the lever H is brought into contact
with the loom handle, and the loom is stopped. If the shuttle passes
safely through the shed, the reed is not pressed back, and the finger
F comes under the frog as the slay gets to the front of its stroke,
and holds the reed comparatively fast. The disadvantage of the loose
reed is that the reed is not sufficiently firm to put a large amount of
weft into the cloth, but improvement is being made in this respect, and
loose-reed looms are to-day made for weaving fabrics for which it was
formerly necessary to have fast reeds.
[Illustration: FIG. 68.]
The invention of the loose reed is generally attributed to Mr. James
Bullough. It was invented about 1842.
THE WEFT FORK STOP MOTION.
[Illustration: FIG. 69.]
One of the most useful adjuncts to the power-loom is the motion for
stopping the loom when the weft breaks or runs out. Fig. 69 will
explain the principle of this useful contrivance. The grid A is placed
at the side of the reed between the reed and the shuttle-box, and the
fork is so placed that as the grid moves forward the prongs of the
fork pass through it. When the weft comes between the fork and the
grid it raises the end of the fork E, out of the way of the hammer
H, which is moved forward every two picks by a cam or lifter, D, on
the bottom shaft of the loom. If the weft breaks or runs out the fork
will of course pass through the grid, and it is so balanced that the
hook E will be caught by the hammer and the loom handle knocked off.
The invention of the Weft Fork Stopping Motion is claimed by several
persons, but it was perfected about the year 1842, when the brake was
applied to it. The action of this brake is illustrated at Fig. 70.
When the handle is pushed sideways in starting the loom it lifts the
rod R and the lever L, and thus takes the brake off. When the handle
is knocked off by the weft fork being caught, the lever L drops and
the brake is applied. The brake power can be regulated by altering the
position of the weight on the levers.
[Illustration: FIG. 70.]
In looms with change boxes at both sides the weft fork is often placed
in the middle of the loom. It is obvious that when several shuttles
are used there will always be some weft threads opposite the grid in
the ordinary weft fork motion, and this renders it inoperative in this
class of looms. It is therefore necessary to have a fork to feel for
each pick separately.
TAKING-UP OR COILING MOTIONS.
There are two distinct classes of taking-up motions--the positive, and
the negative or drag motion. In the former the cloth is taken up a
small but regular distance each pick, and the number of picks per inch
can be regulated to a fraction. Fig. 71 is the common form of positive
take-up motion. A ratchet wheel or “rack wheel,” A, is moved forward
one tooth every pick by a click or catch, M, operated by a projection,
G, on the slay sword. As the slay moves forward the rack wheel is moved
one tooth, and the holding catch or detent N prevents it from going
back. There are five wheels in the train, and the names usually given
to them are as follows: A, rack wheel; B, change wheel; C, stud wheel;
D, stud pinion; E, beam wheel. The emery taking-up roller is marked F.
The cloth, as it is woven, is drawn forward by the emery roller and is
wound upon the cloth roller, which is pressed against the emery roller
by weighted levers, and is turned by friction.
[Illustration: FIG. 71.]
The speed at which the emery beam roller is turned regulates the
number of picks per inch, and as changes are constantly required in
most weaving mills, the wheel B is usually taken as a change wheel.
As this wheel is a driver, a smaller wheel will make the emery roller
move slower, and therefore more picks will be put in the cloth, and a
larger wheel will drive the emery roller quicker, and as a consequence
a smaller number of picks will be put in. If the rack wheel has 50
teeth, the stud wheel 120 teeth, the stud pinion 15 teeth, and
the beam-roller wheel 75 teeth, the beam roller being 15 inches in
circumference, and if the change wheel used has 25 teeth, the number of
picks per quarter-inch will be 20.
This may be proved by multiplying the drivers together and by the
circumference of the emery beam roller in quarter-inches for a divisor,
and multiplying the drivens together for a dividend: the quotient will
be the number of picks per quarter-inch.
DRIVERS.
25
15
---
125
25
---
375
60 quarter-inches
----- in beam
22500
DRIVEN.
50
120
----
6000
75
------
22500)450000(20 picks per
45000 quarter-inch
------
0
When the cloth is taken out of the loom, rather more than this number
of picks will be counted, as there is not the same tension as when the
cloth is being woven. It is usual to allow about 1½ per cent. for
this shrinkage.
For the purpose of easy calculation the dividend of the loom is
obtained; that is, the change wheel required to give one pick per
quarter-inch. By using this as a dividend and dividing by the number
of picks required in a quarter-inch, the quotient will be the change
wheel required; and, _vice versâ_, by dividing by the change wheel, the
number of picks given by that wheel can be obtained.
To find the dividend of a loom--
Multiply the rack, stud, and beam wheel together for a dividend, and
the stud pinion and the number of quarter-inches in a circumference of
the emery beam for a divisor, and the quotient will be the mathematical
dividend. Add 1½ per cent. to this for the practical dividend.
With the wheels given in Fig. 71 the dividend will be as follows:--
15 stud pinion
60 quarter-inches in circumference of beam
---
900
50 rack wheel
120 stud wheel
----
6000
75 beam wheel
----
900)450000(500 mathematical dividend
4500
------
00
500
7 = 1½ per cent. for shrinkage
---
507 =practical dividend=.
Having the dividend, it is only necessary to divide by the picks to
obtain the change wheel required, or to divide by the teeth in the
change wheel to obtain the picks which it will give, thus--
507 507
picks --- = 39 change wheel change wheel = --- = 25⅓ picks.
13 20
The following are the wheels used by various loom makers:
+------+------+-------+------+-------------+---------+
| | | | |Circumference| |
|Rack |Stud |Stud |Beam | of beam in |Dividend.|
|wheel.|wheel.|pinion.|wheel.| inches. | |
+------+------+-------+------+-------------+---------+
| 50 | 120 | 15 | 75 | 15 | 507 |
| 60 | 120 | 15 | 75 | 15 | 609 |
| 50 | 146 | 14 | 90 | 15 | 794 |
| 50 | 100 | 12 | 75 | 15 | 528 |
| 60 | 100 | 12 | 75 | 15 | 634 |
+------+------+-------+------+-------------+---------+
_Example._--Find the dividend of a loom with a rack wheel 60 teeth,
stud wheel 100 teeth, stud pinion 12 teeth, beam wheel 75 teeth,
beam 15 inches circumference.
rack stud beam wheel
60 × 100 × 75
------------------ = 625 mathematical dividend
12 × 60 9 = 1½ per cent.
stud quarter-inches ---
pinion in beam 634 practical dividend.
It is not possible by changing one wheel only to obtain any number
of picks or fraction of a pick, as will be seen from the following
examples:--
507
picks --- = 12·67
40
507
picks --- = 12·12
41
507
picks --- = 12·07
42
For the lower number of picks the motion does fairly well, but for the
higher numbers of picks the changes cannot be made with sufficient
exactitude by changing a single wheel. Even in the lower picks it is
now required to make the smallest fractional changes.
An improved arrangement of wheels is now largely adopted. This is
Pickles’ motion. Fig. 72 shows the train of wheels. The change wheel B
is in this case a driven wheel, and therefore if a larger wheel is used
it will give a larger number of picks in the cloth, and if a smaller
wheel is used it will give a smaller number of picks; so that if the
wheels are so proportioned that the change wheel B has the same number
of teeth that there are picks per quarter-inch, it will always remain
so, whatever size the wheel is. If a 20 driven wheel gives 20 picks, a
30 will give 30 picks, and so on.
The wheel A is also changed, and this is usually called the “standard”
wheel. This is a driver wheel, and therefore a smaller wheel gives
more picks, and _vice versâ_. The wheels are so proportioned that if
A, the standard wheel, has nine teeth, each tooth in B, the change
wheel, represents one pick, and therefore, this wheel being a driven,
the number of teeth in it will also represent the number of picks per
quarter-inch. If an 18 standard wheel is used, it is obvious that the
emery beam will be driven twice as fast, therefore each tooth in the
change wheel B will then represent half a pick per quarter-inch. With a
27 standard each tooth in the change wheel B will represent one-third
of a pick. With a 36 standard each tooth in B will represent a quarter
of a pick per inch.
[Illustration: FIG. 72.]
The wheels mostly used are those in the diagram, and supposing we have
a 36 standard and a 45 change wheel, and taking the emery beam as 15·05
inches in circumference, we get--
B
24 × 45 × 89 × 90
-------------------- = 11·088
36 × 24 × 15 × 60·20
A ·166 = 1½ per cent. for shrinkage
------
11·254 picks per quarter-inch.
Thus with a 36 standard a 45 change wheel, B, gives 11¼ picks per
quarter-inch, or each tooth in the change wheel gives a quarter of a
pick per quarter-inch.
By changing these two wheels any fraction of a pick can be obtained.
Thus if 13½ picks per quarter-inch are required, the wheels used would
be an 18 standard and a 27 change wheel. For 13⅔ picks a 27 standard
and a 41 change wheel would be used, and so on.
The following examples will fully illustrate the principle of this
motion:--
+-------------+--------+------+
| Picks per |Standard|Change|
|quarter-inch.| wheel. |wheel.|
+-------------+--------+------+
| 20 | 9 | 20 |
| 15½ | 18 | 31 |
| 14⅓ | 27 | 43 |
| 14⅔ | 27 | 44 |
| 13¼ | 36 | 53 |
| 13¾ | 36 | 55 |
| 12⅕ | 45 | 61 |
+-------------+--------+------+
It is not always customary to change the wheels in the above manner, as
a different value is often given to each tooth in the change wheel by
altering the standard wheel, otherwise than by multiples of nine.
Any number may be made the basis of a train of wheels of this kind;
there is no reason why it should be nine more than any other number,
and in adapting looms from the ordinary five-wheel motion to this
principle, it is not necessary to get all new wheels, as sow of the old
ones may be made to form part of the train.
There are several kinds of negative or drag take-up motions. One of
the older forms is that given in Fig. 73. A lever, AB, centred at C is
weighted on the arm B. A small cam, D, on the crank-shaft presses down
A every pick and lifts the catch E, which operates the ratchet wheel
F. As the weights drop they act as a drag upon the ratchet wheel. A
small pinion on the same centre as the ratchet wheel drives the wheel
G on the cloth beam. The cloth in a negative motion is wound directly
on to the cloth beam, and thus there is no risk of damaging the finer
fabrics, as is the case when an emery beam is used, as in a positive
motion. The number of picks put in the cloth is regulated by the
weights on the lever B; the greater the weight the less the number of
picks, and _vice versâ_.
[Illustration: FIG. 73.]
The action of a negative motion is as follows:--As the slay beats up,
the cloth between the cloth beam and the reed is slackened a little,
and the weights on the lever at that moment act as a drag upon the
ratchet wheel F. The holding catch is usually a double one, and will
hold the ratchet wheel when taken forward the space of half a tooth.
By increasing the drag upon the ratchet wheel, a slighter blow from
the slay will enable the weights to act, and thus less weft is put
into the cloth. If a loom is regulated so as to put a certain number
of picks per inch into the cloth of a given count of weft, and weft of
a finer count is then used, it is obvious that the number of picks per
inch would be increased. If the weft varies in thickness the negative
motion compensates for this somewhat, by putting more picks in where it
is thinner, and thus a more even thickness of cloth is produced than
where a positive motion is used.
As the cloth is wound on the beam the circumference of the latter
gradually increases, and consequently there would be a gradual
alteration in the amount of weft put into the cloth, owing to the
difference in leverage. It is necessary, therefore, to count the cloth
and adjust the weights at intervals in order to keep the number of
picks regular.
[Illustration: FIG. 74.]
[Illustration: FIG. 75.]
Another kind of negative take-up motion is shown at Figs. 74 and 75.
This is now more generally used than the other kind. The cloth beam
A is driven by a screw, S. The ratchet wheel B is fastened to the
screw-shaft, and the method of operating the ratchet wheel will be seen
from Fig. 75, which is another view of the mechanism. A short lever,
E, is attached to the rocking shaft K, and as the slay moves backwards
from the cloth the weights W are lifted a little, and when the slay
moves forward, the weights, acting through the catch M, will take the
ratchet wheel forward a tooth, or half a tooth, as the case may be.
There is usually a double-holding catch N, which will hold the wheel
if taken forward half a tooth. When the ratchet wheel has made one
revolution, the wheel on the cloth beam will only have been moved one
tooth by the screw, so that the required slow movement of the cloth
beam is obtained by very simple means. There is a hand wheel, P, for
unwinding the cloth readily. The negative motion is used principally
in weaving the heavier classes of cotton fabrics and those in which
there is a large number of picks per inch, such as velvets, and similar
fabrics. Its advantages are that the cloth is wound directly on to
the cloth beam, and cannot therefore be injured by an emery beam, and
that it makes the cloth of a more even thickness, as it compensates
for any variation in the thickness of the weft; and its disadvantages
as compared with a positive motion are that it requires frequently
adjusting (less frequent, of course, when a very large number of picks
are put in, as in velvets), and that it does not put a perfectly
regular number of picks in the cloth, as a positive motion does. This
latter is the chief objection to it, as even in the lighter makes of
common velvets a positive motion is preferred on account of its giving
a more evenly picked cloth. In silk looms, where it is absolutely
necessary to dispense with an emery beam, a very large cloth beam is
used, and the cloth is wound directly on to the cloth beam although
the take-up is positive. The cloth beam is sometimes over a yard in
circumference, so that it will hold a fair length of cloth without
making much difference in the number of picks. The cloth is taken
off the beam frequently, or the gradual change in the thickness of
the cloth beam would cause the piece to get too thin. This would, of
course, not do for cotton goods.
Another ready method of obtaining any required pick in a positive
motion is used in the East Lancashire districts. Seven wheels are used,
as in Pickles’ arrangement, but the ordinary wheels of a 507 dividend
(or other dividend) are used, and in addition the two wheels B and
C, as in Pickles’ (Fig. 72), are introduced. The wheel B, the driven
wheel, is called the standard in this arrangement; and suppose it is
required to put 15 picks per quarter-inch in the cloth with the rack
wheel 50 teeth, stud wheel 120, stud pinion 15, beam wheel 75, beam
15 inches circumference. The standard used is a 24--this, it must be
borne in mind, is in this case a driven wheel. Then by multiplying the
dividend of the five-wheel motion, viz. 507·5, by 24, the teeth in the
standard, and dividing by the picks per quarter-inch required, we get
the product of the two drivers, A and C, thus--
507·5 × 24 standard B
--------------------- = 812
15 picks
This 812, then, is the product of the two drivers, and any two
convenient wheels which, multiplied together, give this number can be
used--thus 812/28 = 29. Therefore the two drivers may have 28 and 29
teeth respectively. The two wheels are found by experiment. If the
dividend of the five wheels is 609 a 20 standard wheel is used, and
the same drivers as in the preceding case will do. If it is required
to change only one wheel, and to have the arrangement such as to
give an exact number of picks, or half-picks, or quarter-picks, in
the quarter-inch of cloth, by taking the two drivers A and C of such
numbers that their product amounts to 507, the number of teeth in the
driven wheel B will always equal the number of picks per quarter-inch
exactly. Thus 507/13 = 39. Therefore if the drivers A and C have
respectively 13 and 39 teeth, every tooth in the driven wheel B will
represent one pick per quarter-inch.
Suppose half-picks are required exactly, the method of obtaining the
wheels is as follows:--Multiply the 507·5 by 2, which equals 1015, then
find two convenient wheels which, multiplied together, produce this
number; 35 × 29 = 1015, and the two drivers A and C may be 35 and 29.
This will cause every tooth in the driven wheel B to represent half a
pick exactly.
Thus with a 35 wheel A, and a 29 wheel C, a 31 wheel B will give 15½
picks per quarter-inch, the other wheels being the same as in an
ordinary 507 dividend motion.
The following examples will prove this:--
50 rack × 31 B × 120 stud × 75 beam wheel
------------------------------------------- = 15·27
35 A × 29 C × 15 pinion × 60 quarter-inches
and 15·27
0·23 = 1½ per cent. shrinkage
-----
15·50 picks.
When quarter-picks are required exactly, by changing one wheel
only--multiply 507·5 by 4, and the product of the two drivers A and C
must equal this. Then every tooth in the driven wheel B will represent
a quarter-pick per quarter-inch.
There are many methods of letting off the warp positively, but none are
likely to succeed in displacing the older and quite satisfactory method
of levers, ropes, and weights. The very fact of making the let-off
positive, causes too great a rigidity in the hold of the warp, which
is detrimental to the yarn. The frictional let-off is not likely to be
replaced in cotton goods weaving unless it be in some of the heavier
kinds of fabrics. Where it is a question of putting in as much weft as
possible, the positive let-off has an advantage.