CHAPTER XXIII
Sewing Machines
Fig. 132. Lock-stitch machine.
1. Bed Slide
2. Presser Foot
3. Presser Foot Thumb Screw
4. Needle Clamp
5. Needle Clamp Thumb Screw
6. Needle Bar Thread Guide
7. Needle Bar Bushing
8. Thread Cutter
9. Face Plate Thumb Screw
10. Slack Thread Regulator
11. Tension Spring
12. Tension Regulating Thumb Nut
13. Tension Discs
14. Thread Take-up Spring
15. Thread Guide
16. Presser Bar Lifter
17. Face Plate
18. Pressure Regulating Thumb Screw
19. Presser Bar
20. Thread Take-up Lever
21. Thread Guide
22. Arm
23. Spool Pin
24. Bobbin Winder Stop Latch
25. Belt Cover
26. Bobbin Winder Thread Guide
27. Balance Wheel
28. Bobbin Winder Pulley
29. Bobbin Winder Spindle
30. Bobbin Winder Worm Wheel
31. Stitch Regulating Thumb Screw
32. Bed
33. Throat Plate
34. Feed Plate
234. Different Types of Sewing Machines. There are two types of sewing machines in use—the chain-stitch and the lock-stitch. Sewing machines are made to run by hand, foot or mechanical motor power. This makes no difference in design or care of the stitching part of the machine. Motor and foot power run the machine faster than hand power.
The treadle of the foot-power machines swings on pivots. These should be kept oiled and clean from lint and thread. The large and the small wheels for the belt should be oiled at the axle.
235. Lock-Stitch Sewing Machine. A lock-stitch sewing machine (Figs. 132 and 133) consists of shafts and wheels which move the needle, feed plate and bobbin. The top thread is guided from spool to needle thru a tension so that only the needed amount passes forward each time the needle is raised after the thread has caught in the cloth.
When there is a difference in the size of the thread used on the machine, the tension must be adjusted to fit the thread, unless the tension is automatic. If the tension is not properly adjusted or the machine threaded properly, the thread will either break, tangle at the needle point, or draw the top thread tighter than the bottom one (Fig. 134).
A longer stitch is needed for coarse thread than for fine thread.
236. Feed Plate. A device below the needle called the feed plate (No. 34, Fig. 132) shoves the cloth faster or slower under the needle, according to its adjustment, thus making a longer or shorter stitch. This device is a rough plate which moves backward each time the needle is raised, and forward again when the needle comes down. While moving backward, the rough surface moves the cloth, but it drops slightly below the level of the table as it moves back into place, so does not affect the cloth. For short stitches, it moves with a short stroke, and for long stitches, with a long stroke. If the feed plate becomes gummed with lint and oil, the machine will not make even stitches and may fail to move the cloth. Sometimes it will fail to stitch. Improper threading may break the needle thread. Too tight a tension may break it. Too coarse thread for the size of the needle may break the needle. A bent, blunt pointed or incorrectly set needle may break.