What are the most important things to know in sewing engineering?
The basic rules of feed adjustment and tension settings, the effect of the thread check spring, sewing parts, and basic adjustments using an adjustment gauge.
The basic rules of feed adjustment and tension settingsThread tension and stitch formation are directly connected with the feed adjustment. The thread tension must be greater than the sum of resistances (friction) on the thread while it is passed around the hook. During the sewing action the needle thread is subjected to strain caused by friction and tensile forces, especially the peak loads caused by acceleration and subsequent pulling forces on the thread. Friction of the thread in the material and on the sewing parts is at its lowest when the needle penetrates while the workpiece is still over the needle hole. This is the reason for the basic rule of feed adjustment (not applicable to needle-feed machines): the feeding movement should take place as late as possible, theoretically not until the take-up lever is at the top of its stroke. The feeding movement must be completed, however, when the needle enters the sewing material again.
The effect of the thread check springIndirectly this increases the tension on the thread while it is resting in the thread tension and is subjected to a sudden pulling force. Consequently, the tension on the moving thread (when it is pulled through the tension mechanism) is less. This is more favourable for the required smoothness and elasticity of the seam and lessens the tensile strain on the thread and its proneness to breakage.
Sewing partsEquipment of a sewing machine with the optimum sewing parts (needle plate, feed dog, presser foot, guides, etc.) is often decisive for seam quality, sewing reliability and the sewing output of the machine.
Basic adjustments using an adjustment gaugeThe basic adjustment of the sewing machine comprises the optimum adjustment of the machine, as determined by calculations and extensive trials. In the final stages of production every sewing machine is adjusted to its basic settings with the aid of gauges and tested for its sewing reliability according to a specified programme. Every mechanic should be able to check and correct the basic settings of a machine using adjustment gauges in a relatively short time. Experience shows that 90% of all sewing disturbances are due to incorrect basic adjustments. Only the remaining 10% are due to real sewing problems which can be remedied by normal means, e.g. use of the correct machine type or special sewing parts.