SEWING MACHINE TYPES


Deutsch: Nähmaschinenmechanismus. English: An ...
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Sewing is a creative and interesting skill. The knowledge of sewing give a confident feeling when it is applied to the construction of garments. The earlier method of sewing by hand is not applicable for all stages of garment making. Therefore, considerable emphasis is given to machine sewing. There are several machines in the market today, each with its own desirable features and advantages. Sewing machines range from most basic having only simple lock stitch to the electronic machines that use advanced computer technology having various functions for example piping, binding, ruffling, pleating, darning, hemming and even making buttonholes and attaching fasteners. A good sewing machine is required to obtain quality products. One has to be familiar with the characteristics of different types of machines for selecting appropriate machine, depending upon the ability and requirements of the person.

TYPES OF SEWING MACHINES:

Sewing machines are now available in various models such as domestic model, tailor model, industrial model, portable and cabinet models. They may be operated by hand, treadle or electric motor.

Hand – Operated Sewing Machine:

This is the simplest form of sewing machine which is operated by hand. A detachable handle provided to the flywheel is used to operate the machine. This machine is generally suitable for domestic purpose because it does not help in speeding up the work.

Treadle Sewing Machine:

This machine is exactly like the hand sewing machine but it is operated by foot using an additional stand. In this type the balance wheel is operated by a belt with the help of lower stand, which is driven by feet. This machine operates faster than that of the hand-operated machine. This machine is suitable where there is no power supply. When handling
this machine both the hands are free to handle the fabric, speeding up the work. Even some of the heavy-duty machines are operated by this method.

Electric Sewing Machine:

This is the fastest sewing machine. One needs practice to handle it. In an electric machine the balance wheel comes to motion by a belt, which is attached to an electric motor.

PARTS OF A SEWING MACHINE AND THEIR FUNCTIONS:

The basic structure of sewing machine is the same whether it is hand-operated sewing, treadle sewing machine or electric sewing machine. The basic parts of a sewing are listed below and seen in Fig.1

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1. Spool pin: It is fitted on top of the arm to hold the reel.

2. Thread guide: It holds the thread in position from the spool to the needle.

3. Tension disc: The two concave discs put together with the convex sides facing each other. The thread passes between the two. The tension of the thread is adjusted by a spring and nut which increases or decreases pressure

4. Take up lever: It is a lever fitted to the body of the arm. Its up and down motion feeds the thread to the needle and tightens the loop formed by the shuttle.

5. Needle bar: This is a steel rod to hold the needle at one end with the help of a clamp. Its main function is to give motion to the needle.

6. Bobbin case: This moves into position to catch the top thread and form the stitch as the needle is lowered into the bobbin chamber.

7. Presser foot: It is fixed to the presser bar to hold the cloth firmly in position when lowered.

8. Presser foot lifter: A lever attached to the presser bar for raising and lowering the presser foot.

9. Stitch regulator: This controls the length of the stitch.

10. Bobbin winder: A simple mechanism used for winding thread on the bobbin.

11. Fly Wheel: When this is made to revolve, it works the mechanism of the motion

12. Clutch or Thumb Screw: This is in the center of the fly wheel and it engages and disengages the stitching mechanism.

13. Slide Plate: A rectangular plate, which facilitates the removal of the bobbin case without lifting the machine.

14. Needle Plate or Throat Plate: A semi-circular disc with a hole to allow the needle to pass through it.

15. Feed dog: This consists of a set of teeth fitted below the needle plate. It helps to move the cloth forward while sewing.

16. Face plate: A cover which on removal gives access to the oiling points on the needle bar, presser bar and take-up lever.

17. Spool pin for bobbin winding: Spool of thread is placed on this at the time of bobbin winding.

PREPARATION FOR STITCHING

Before starting actual machining, you should check that the needle of the machine is of correct size, is sharp and correctly set. The bobbin should be evenly set. Briefly, the various steps of prepreparation are:

• Winding the bobbin
• Upper Threading
• Drawing the bobbin thread
• Tension adjustments
• Pressure and feed adjustments
• Selection of thread and needle

A perfect stitch can be obtained only when the thread selected is suitable to the material to be stitched and the needle is of the correct size. For stitching on delicate thin fabrics, use fine thread and fine needle. For heavy fabrics, needles and thread size should be larger. The following Table 1 will be a guide to help selection of appropriate needle and thread sizes.

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Types of Threads

The natural fibre threads available in the market are cotton and silk. Synthetic threads are usually made from polyester and terylene. Threads whether natural or synthetic are produced in various thickness: higher the number, finer is the thread and smaller the number, coarser is the thread. It is important to remember that the same thread should be used for the bobbin and top spool.

Selection of needles

Machine needles are selected according to the weight and other characteristics of the fabric, as well as the thread type being used for construction. Generally, a needle should be fine enough to penetrate the fabric without damaging it and yet have an eye, which is big enough so that the thread does not fray or break. Needles come in various sizes, from very fine (size 9) for light weight fabrics to thick (size 18) for very heavy weight and dense fabrics.

COMMON MACHINE TROUBLES

The sewing like any other machine, gives troubles of stitching like thread breaking, uneven stitching, puckering, bending and breaking of needle, looping of threads, skipping of stitches, etc. Little problems with the sewing machine can be very irritating and time consuming. They can happen to even the most experienced seamstress. A person operating the machine should be able to rectify these and solve the problems. Some of the common machine problems are listed below:

• breaking needles
• looping of stitches
• skipping stitches
• variation in stitch length
• puckered seams
• upper thread breaking
• lower thread breaking
• machine not feeding properly
• machine working heavily
• layers feed unevenly
• fabric does not feed in straight line
• cause damage to fabric
• Puckering on both layers of fabric
• Puckering on under layer only
• Shows feed marks on the under side
• Fabric is damaged or holes around the stitches

CARE AND USE OF SEWING MACHINES

A sewing machine needs care for its smooth running. It should be cleaned and oiled regularly to ensure satisfactory sewing and long life. When not in use, your machine should be covered to prevent dust accumulation on it. Use a small dry brush or old toothbrush and soft cloth to remove dust and lint. You should always remove lint deposits, dust and thread bits before oiling any part of the machine. Use a pointed instrument like a needle to pick out the bits of thread and lint that cannot be brushed out.

It is necessary to oil and lubricate the machine periodically. If the machine is used everyday, oil it once a week. After oiling, wipe off the surplus oil and place a piece of folded fabric under the presser foot to absorb any excess oil. To oil thoroughly, remove the upper thread, needle plate, slide plate, face plate, bobbin case, needle and presser foot. Oil the holes on the underside first, after cleaning and then proceed to the upper side. Use only few drops of oil in each hole. Never use coconut oil. Machine oil of different brands may be used for different models of sewing machine, but should be used as recommended in the instruction book.

If the machine becomes gummed with oil, put a drop of kerosene or petrol in each oil hole and joints and run it rapidly for several minutes. Wipe off and re-oil it with machine oil. The motor of electric sewing machine should be greased periodically.

Summary
The knowledge of sewing give a confident feeling when it is applied to the construction of garments. The various parts of a sewing machine and their functions helps one  to understand the working of a sewing machine. A brief up on the common machine problems help us to understand and rectify the problems. Above all the care of sewing
machine is rather important for a long service of the machine.

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Sample Warping


This warping process, which was developed for sampling purposes, gives full proof of its performances during this production phase of new items. This particular process is composed of several warping operations which wind up a limited thread length and place on the warping width several bands of different colours to get the colour variants of the fabric. This kind of warps can be obtained also by section warping, which however involves a considerable loss of time owing to frequent cone changes and definitely higher investments in raw materials. In practice a cone per colour is sufficient to obtain any required warping sequence. The machine is composed of a small creel where the cones of the warping sequence are placed, by a thread guide which winds up a preset number of meters (selectable with a pattern or a control device) taken from the cone according to the thread sequence in progress. The latest solution with revolving creel permits to wind up to 12 threads at a time at a winding speed of max. 1200 meters/minute. Once the winding operation is concluded, the threads are beamed on a weaver’s beam which follows the usual production cycle. The machine manufacturers proposed initially two solutions for this kind of warpers: the first solution envisaged a vertical development of the winding blanket, whereas according to the latest solution the threads are pre-wound on a drum before being wound on the weaver’s beam. The warp length in this last model varies from 7 to 420 meters; some weavers consider this length as normal for their productions and therefore use this system side by side with the traditional sectional warping machine. It is evident that the correct use of this machine permits to feed the weaving machine in a very short time while minimizing the use of materials and labour, especially if an automatic drawing-in equipment is available upstream.

Simple Spot Designs


Designs in which the ornament consists chiefly of small, detached spots or figures are employed and where elaborate figure ornamentation is not desired. Spotted effects are produced in cloths in different ways—e.g., by employing fancy threads in which spots of contrasting color occur at intervals, and by introducing extra warp or extra weft threads which are brought to the surface where the spots are formed. In the following, however, only the system of producing spot figures is considered in which the spots are formed by floating the ordinary weft or warp threads on the surface of the cloth in an order that is in contrast with the interlacing in the ground. The figures show most prominently when the warp and weft threads are in different colors or materials; but if the two series of threads are alike the difference in the reflection of the light from the different weave surface is sufficient to render the figures clearly visible. Other things being equal, the weft usually forms brighter and clearer spots than the warp: (1) because it is more lustrous and bulky
on account of containing less twist; and (2) because cloths generally contract more in width than in length, the weft thus being brought more prominently to the surface than the warp.

Methods of drafting spot figures

Simple spot figures are readily designed directly upon point paper, and the outline may be first lightly indicated in pencil, as represented at A. The squares are then filled in along the outline, as indicated at B, and this is followed by painting the figure solid, as shown at C. If the ground weave is plain, in painting the outline, the moves should be in odd number of squares, as shown at D, in order that the edge of the figure will fit correctly with the plain marks. If only short floats are required in the figure a simple weave (e.g., a twill or sateen) may be inserted upon it in a color of paint that is in contrast with the first color as represented by the blanks E. On the other hand, the binding marks may be inserted in such a manner as to give a special appearance to the figure as indicated at F. The prominence of the figure is usually reduced about in proportion to the firmness of the binding weave, but, as a rule, a float longer than 0.5 cm should not be made or the structure will be too loose.

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Spot figures which are rather intricate may be sketched upon plain paper and then be drafted upon design paper in the manner illustrated at I, J, and K.

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Distribution of spot figures

It is only in special cases, when a spot is arranged to fit in the cell of a colored check, that a figure is used only once in the repeat of a design. Generally, two or more figures are contained in the repeat, and it is necessary for them to be placed at a suitable distance apart, and evenly distributed over the repeat area. The repeat must be at least so large that
the figures do not encroach upon each other, and the factors which influence the number of ends and picks in a repeat are as follows:

(a) The size and shape of the figure;

(b) the number of figures;

(c) the amount of ground space required;

(d) the number of threads in the repeat of the ground weave. Even distribution of the figures is secured by employing a simple weave—such as plain and certain sateens—as the basis of the arrangement.

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A method of distributing figures upon design paper, that will be found applicable to any shape of figure, is illustrated, which shows the spot L arranged in the order of the 5-sateen base given at M upon 30 ends and 40 picks. As shown at N, the figure is first painted in near the bottom left-hand corner of the sheet of point paper, and the square which is nearest its centre is marked, as indicated by the cross on the fifth end and sixth pick. From the marked end and pick the repeat is divided in both directions into as many parts as figures to be used—in this case five; and lines are lightly ruled in pencil on the spaces, as represented by the shaded lines in N. It will be seen that the vertical lines occur at intervals of six ends and the horizontal lines at intervals of eight picks to correspond with the division into five parts each way of the repeat of 30 ends and 40 picks. Then, as indicated by the rosses in N, the squares where the divisional lines intersect are marked in the order of the sateen base. The final stage in designing the figures consists of copying the first spot square by square in the same relative position to each centre mark, as shown at O.

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In the plain weave basis the figures are arranged in alternate order, as shown in the example given and the corresponding design indicated at A. In this case, as there are two figures in the repeat, the number of ends and picks in he design are divided into two parts from the eighth end and pick which form the centre of the first spot.

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Theory and calculation of cover factor


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The figure shows projected views of two woven cloths of different construction. At A the warp and the weft threads cover the area of the cloth only partially, but at B the cloth area is covered completely with no spaces left between the adjacent warp yarns, and it will be seen that the relative closeness of yarns in a woven cloth is dependent upon the ratio of yarn diameter, d, to yarn spacing, p. This ratio known as relative cover, can be defined as the proportion of a projected view of a given area of cloth which is covered by threads, and will have a scale from 0 to 1, although it may also be expressed as percentage cover with a scale from 0 to 100 per cent.

d/p = relative cover,
(d x 100)/p = percentage cover

It is preferable to express warp and weft relative cover separately, as the cumulative value of cloth cover does not indicate the comparative importance of each set of yarns which is essential for the determination of certain cloth characteristics.

From the relationship shown above it will be obvious that if d= p. the value of relative cover is one, and this is regarded as the theoretical maximum cover. In practice, however, this value can be exceeded  considerably in any one direction, either through yarn distortion, or, by forcing the threads into different planes, especially if the relative cover of the opposite set of threads is reduced correspondingly.
The relative cover for one thread system can be calculated as follows by considering an area of 100 x 100mm:

Area per thread = 100 x d
Area covered by n threads of one system = n x 100 x d
Therefore, relative cover = (n x 100 x d)/(100 x 100) = (n x d)/100

Example: The cloth represented at A is specified as follows: Warp — 25 tex cotton, 267 ends/100 mm; weft—36 tex cotton, 334 picks/100 mm. Find the relative warp and weft cover. (Subscript 1 refers to warp, subscript 2 to weft.)

Warp relative cover = (n1 x d1)/100
= (267 x (25)/(26.7))/100
= 0.50

Weft relative cover = (n2 x d2)/100
= (334 x (36)/(26.7))/100
= 0.75

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