The Sewing Machine Needle

Structure of the sewing machine needle:

The functions of the sewing machine needle in general are:

a)      To produce a hole in the material for the thread to pass through and to do so without causing any damage to the material;

b)      To carry the needle thread through the material and there form a loop which can be picked up by the hook on the bobbin case in a lockstitch machine or by the looper or other mechanism in other machines;

c)      To pass the needle thread through the loop formed by the looper mechanism on machines other than the lockstitch machine.

With the functions of the sewing machine described it is now appropriate to study the details of the separate parts of the needle and their role in satisfactory seam construction and performance.

The shank is the upper part of the needle which locates within the needle bar. It may be cylindrical or have a flat side, according to how it is secured into the machine. It is the support of the needle as a whole and is usually larger in diameter than the rest of the needle for reasons of strength.

The shoulder is the section intermediate between the shank and the blade, the latter forming the longest part of the needle down to the eye. The blade is subject to the greatest amount of friction from the material through which the needle passes. In needles designed for use in high speed sewing machines the shoulder is often extended into the upper part of the blade to give a thicker cross-section which just enters the material when the needle is at its lowest point on each stitch. This supplementary shank or reinforced blade strengthens the needle and also enlarges the hole in the material when the needle is at its lowest point, thus reducing friction between it and the material during withdrawal after each stitch. Alternatively, the blade can be gradually tapered along its length from shank to tip, as another way of reducing friction.

The long groove in the blade provides a protective channel in which the thread is drawn down through the material during stitch formation. Sewing thread can suffer considerably from abrasion during sewing as a result of friction against the fabric and a correctly shaped long groove, of a depth matched to the thread diameter, offers considerable protection to the thread.

The short grove is on the side of the needle which is towards the hook or looper and is a groove which extends a little above and below the eye. It assists in the formation of the loop in the needle thread.

The eye of the needle is the hole extending through the blade from the long groove on one side to the short groove on the other. The shape of the inside of the eye at the top is critical both in reducing thread damage as the needle penetrates the material and in producing a good loop formation.

The scarf or clearance cut is a recess across the whole face of the needle just above the eye. Its purpose is to enable a closer setting of the hook or looper to the needle. This ensures that the loop of needle thread will be more readily entered by the point of the hook or looper.

The point of the needle is shaped to provide the best penetration of each type of material according to its nature and the appearance that has to be produced. It is also the part of the needle which must be corrected selected in order to prevent damage to the material of the seam being sewn.

The tip is the extreme end of the point which combines with the point in defining the penetration performance.

Sewing machine needles can be classified based on the below:

        I.            Needle type number – is based on the eye of the needle, finish, groove, point, shaft and total length.

      II.            Needle size number – Needles are available in a wide range of sizes and the choice of size is determined by the fabric and thread combination which is to be sewn. Different needle manufacturers use their own nomenclature to describe needle sizes but the simplest sizing system is the metric one. The metric size or Nm of a needle is related to the diameter at the point at the middle of the blade above the scarf or short groove but below any reinforced part. This measurement, in millimetres, multiplied by 100, gives the metric number. Thus a diameter of 0.9mm is an Nm 90; a diameter of 1.1mm is an Nm 110.

    III.            Length – is the distance from the top of the needle to the centre of the eye.

    IV.            Shape – Refers to the shape of the blade, which can be straight or curved.

      V.            Point – based on the shape and size of the point the needles are classified as:

Needle Point shapes

Cutting edge needle stitches on leather

1.      Set point – Have a fine, sharp point and thus are used for stitching of woven fabrics as they pierce between the adjacent yarns in the compactly woven fabric structures and do not break the yarns. There three sub-types possible:

a)      Slim set point – Are used for blind stitch on fine and densely woven fabrics as they can penetrate the yarns of the fabric without rupturing them.

b)      Set cloth point – Has a slightly rounded point that displaces the yarns of the fabric without damaging them. This is the most versatile point shape.

c)      Heavy set point – The point of these needles is strongly blunted making them best suited for button sewing.

2.      Ball point – As the name suggests, this needle type is identified by its rounded, smooth point which makes its way in between the yarns in woven and knit constructions. This point does not pierce into the yarns, but displaces them away making a hole to guide the needle thread through it.

a)    Light ball point – are used for sensitive fabrics such as knits, to prevent damage to the loops.

b)      Medium to heavy ball point – are used to sew with elastomeric threads and on elastic material containing rubber.

3.      Cutting edge/ point – Are used for sewing leather, films, coated or laminated textiles. The Philips screwdriver shaped pint of this needle cuts through these fabrics making a large enough hole to allow the thread to pass through it. The possible shapes of the point could vary from triangular to star shape, having sharp sides and sharp blade.

Needle needs to be replaced when

• Broken or shredded threads
• Skipped or uneven stitches
• Puckered or damaged fabric
• Popping sounds made by the sewing machine

A bad or improper needle can:

1.      Damage the fabric.

2.      Fray and break the sewing thread.

3.      Increase downtime.

4.      Give poor seams that cannot withstand strain.

5.      Result in poor quality stitching, skipped stitch etc.

6.      Can damage the sewing machine itself by damaging the hook and looper points.