Sewing Machine Needles

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The size of the shoulder depends on the size of the shank and the blade. The blade The end of shoulder to the top of eye is the blade. The blade contacts the material being sewn during sewing, the blade is subjected to higher frictional forces. The blade has a long groove and a short groove. The blade is sometimes made smaller in diameter over a part of its length extending from just above the eye. This is done to minimize needle – cloth friction. Care should be taken to avoid making the needle too blade diameter in this way.
Long groove The long groove is the protective channel for the needle thread during the cycle of stitch formation. The sewing thread is subjected to high abrasion during sewing as it penetrates through the material so many times. The long groove gives somewhat protection for the thread. Short groove This is the reduced area above and below the eye of the needle and is situated at the loop-taking side of the needle. It assists the formation of loop. Scarf or clearance cut This enables a closer setting of the hook or looper to the needle. It is just above the eye on the loop taking side of the needle.
Scarf permits a close setting of the shuttle hook or looper to the needle. Eye The eye is the hole which goes through the blade from the long groove to the short groove. It enables to pass the needle thread. To avoid thread breakage during sewing, the eye should have a smooth surface. The thread should pass freely through the eye but not too loosely. Otherwise it will interfere with proper loop formation. Point The point of needle can have different shapes. The type of point should be correctly chosen in order to prevent any damages to the material being sewn. The main function of the point is penetration of the material.
Tip Tip is the extreme end of the point. Tip also can take different shapes. Needle manufacturers commonly recommend sharp tip round point needles for stitching the majority of woven cloths. Round tip and ballpoint needles are recommended for knitted fabrics. 3Types of needle points There are two main types of needlepoint. (i)Cutting point (ii)Cloth point The selection of the type of the point depends on the material to be sewn. Some types of materials such as textile fabrics (woven, knitted or non-woven) have spaces within the structure, while some other types such as leather or plastics does not have gaps in the structure.
Cloth point needles Cloth point needles are mainly used for sewing textile materials. These enable the needle to penetrate fabrics whether woven, knitted or non-woven, easily without damaging the yarns or fibers. There are different types of cloth point. (i)Round ball point (ii)Light ball point (iii)Medium ball point (iv)Heavy ball point Round point As you can see in the figure. 2 the round point has a semi circular shape and the cross-section is having a circular shape. This type is widely used in sewing machines to sew textile materials such as warp knitted fabrics and light to medium weight woven fabrics.
Figure 2 Round point needle Light ballpoint The point of the needle takes a ball shape as in the figure 3. The cross section is circular. It has a less possibility to damage the material since it is having a ball-shape. The diameter of the tip is one quarter of the blade diameter. Figure. 3 Light ball point Medium ball point :- The shape of the medium ballpoint is similar to the light ballpoint but the diameter of the medium ball is larger than the light ballpoint. It has a greater penetration power than the light ballpoint. You can see the shape, cross section of the medium ballpoint in figure 4
Figure 4 Medium ball point Heavy ball point :- Very much similar to the medium ball point but the diameter of the tip is about half of the blade’s diameter. This type is used to sew medium to heavy weight woven fabrics and elastic materials. It is clearly seen in the figure 5 Figure 5 Heavy ball point Cutting point needles This type is used to sew leather and non-textile materials, which do not have gaps within the structure. Needle must be able to cut the material layer to facilitate its penetration. Therefore this type of tips have cutting edges.
The cutting points are made with a variety of shapes to suit for different types of materials. The common types are Narrow wedge point Cross point Narrow twist point Narrow reverse point Triangular point & Square point Narrow wedge point In this type of tip, the point is at right angles to the sewing direction. You can clearly understand it from the figure 6 Figure 6 Narrow wedge point This type is most commonly used and is suitable for shorter length stitches and for light to medium grade leather. Cross point The cross section of the cross point takes a lens shape.
Here it is parallel to the sewing direction so that short stitch lengths are not feasible with this type of point. Therefore it is only suitable for long stitch lengths. You can see it clearly in the figure
The difference between the narrow twist point and the narrow reverse point is that the cuts made by them are at opposite directions. Figure 9 Narrow reverse point Triangular point As its name implies, the cross section is triangular in shape as shown in figure 10. Although it has a good penetration power, the loss of strength in the material is due to the cutting effect, which is very much higher than in other types. This type is suitable for hard & thick leather. Figure 10 Triangular point Square point The cross section takes squared shape as shown in the figure 11 The loss of strength in the material due to the cutting effect is higher.
This is best suited for leather, which has a coarse surface structure. Figure 11 Square point 4Needle sizing There are different types of sewing machine needles now available. The needles are also available in a wide range of sizes. The selection of the correct size of needle is essential to make a good seam. If the needle is too small for the thread, it is difficult to pass the thread through the eye as well as it will not fit properly in the long groove and will subject to a high abrasion. If the needle is too big it will make poor control of stitches and tends to make slipped stitches.
In order to select the best needle size, there should be common methods of sizing. Different manufacturers use different methods or scales to give the size of needles. The commonly used systems are metric system, inch system and the singer system. The metric system The metric system is related with the diameter of the needle blade above the scarf, but not at any reinforcement of the blade. The diameter in millimeters multiplied by hundred gives the metric number of needle. For an example, Nm 80 sewing machine needle has a blade diameter of 0. 8mm. The inch system

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2.3.15 Consider a manufacturing process that is producinghypodermic needles tha

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2.3.15 Consider a manufacturing process that is producinghypodermic needles that will be used for blood donations.Th ese needles need to have a diameter of 1.65 mm—too bigand they would hurt the donor (even more than usual), toosmall and they would rupture the red blood cells, renderingthe donated blood useless. Thus, the manufacturing processwould have to be closely monitored to detect any significantdepartures from the desired diameter. During every shift ,quality control personnel take a sample of several needlesand measure their diameters. If they discover a problem, theywill stop the manufacturing process until it is corrected.a. Define the parameter of interest in the context of thisstudy and assign an appropriate symbol to it.b. State the appropriate null and alternative hypothesesusing the symbol defined in (a).c. Describe what a Type I error would be in this study. Also,describe the consequence of such an error in the contextof this study.d. Describe what a Type II error would be in this study.Also, describe the consequence of such an error in thecontext of this study.2.3.16 Recall that the two errors discussed in this chapterwere regarded as “false alarm” and “missed opportunity.”In some fields, these errors are also regarded as “consumer’srisk” and “producer’s risk.” With regard to the previousexercise about the hypodermic needle manufacturing process,do you think the Type I error is the consumer’s risk orthe producer’s risk? What about the Type II error?
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2.2.19 Consider a manufacturing process that is producinghypodermic needles tha

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2.2.19 Consider a manufacturing process that is producinghypodermic needles that will be used for blood donations.These needles need to have a diameter of 1.65 mm—too bigand they would hurt the donor (even more than usual), toosmall and they would rupture the red blood cells, renderingthe donated blood useless. Thus, the manufacturing processwould have to be closely monitored to detect any significantdepartures from the desired diameter. During every shift ,quality control personnel take a random sample of severalneedles and measure their diameters. If they discover aproblem, they will stop the manufacturing process until itis corrected. For now, suppose that a “problem” is when thesample average diameter turns out to be statistically significantly different from the target of 1.65 mm.a. Identify the variable of interest and whether the variableis categorical or quantitative.b. Write the appropriate hypotheses using appropriate symbolsto test whether the average diameter of needles from themanufacturing process is different from the desired value.c. Suppose that the most recent random sample of 35 needleshave an average diameter of 1.64 mm and a standarddeviation of 0.07 mm. Assign appropriate symbols tothese numbers.d. Suppose that the diameters of needles produced by thismanufacturing process have a bell-shaped distribution.Sketch the distribution of the average diameter of samplesof 35 needles, assuming that the process is not malfunctioning.Be sure to clearly label the axis of the graph andprovide values for what you think the mean and standarddeviation for this distribution should be.3.3.4 According to a 2011 report by the United StatesDepartment of Labor, civilian Americans spend 2.75 hoursper day watching television. A faculty researcher, Dr.Sameer, at California Polytechnic State University (Cal Poly)conducts a study to see whether a different average appliesto Cal Poly students. Suppose that for a random sample of100 Cal Poly students, the mean and standard deviation ofhours per day spent watching TV turns out to be 3.01 and1.97 hours, respectively. The data were used to fi nd a 95%confidence interval: (2.619, 3.401) hours/day. Which of thefollowing are valid interpretations of the 95% confidenceinterval? For each of the following, statements, say whetherit is VALID or INVALID.a. About 95% of all Cal Poly students spend between 2.619and 3.401 hours/day watching TV.b. There is a 95% chance that, on average, Cal Poly studentsspend between 2.619 and 3.401 hours/day watching TV.c. We are 95% confident that, on average, these 100 CalPoly students spend between 2.619 and 3.401 hours/daywatching TV.d. In the long run, 95% of the sample means will be between2.619 and 3.401 hours.e. None of the above.
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