SINGER 29K73 - Manual (Page 13)

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For perfect stitching, the tension on needle and
bobbin threads must be heavy enough to pull threads
to center of material and make a firm stitch, thus:
TENSIONS
Fig. 23. Perfect Stitch
If the tension on the needle thread is too tight, or
if that on the bobbin thread is too loose, the needle
thread
will lie straight along the upper surface of
the material thus:
The tension on bobbin thread is regulated by the
screw in Figs. 27 and 28 on the end of the shuttle
tension spring.
To increase bobbin thread tension, gradually tighten
screw. See Fig. 27.
To decrease bobbin thread tension, gradually loosen
screw. See Fig. 28.
When bobbin thread tension has been properly
adjusted, it is seldom necessary to change it because
a correct stitch can be usually obtained by varying the
needle thread tension.
BOBBIN THREAD TENSION
Fig. 24. Tight Neecile Thread Tension
If the tension on the bobbin thread is too tight, or
if that on the needle thread is too loose, the bobbin
thread will lie straight along the under side of the
material, thus:
Fig. 27. Increasing Bobbin Thread Tension
Fig. 25. Loose Needle Thread Tension
NEEDLE THREAD TENSION
The tension on the needle thread is regulated by
the thumb nut near the tension discs. See Fig. 26.
To increase the needle thread tension, tighten thumb
nut.
To decrease the needle thread tension, loosen thumb
nut.
NOTE: Tension on needle thread can be tested only
when the feeding foot is down.
Fig. 28. Decreasing Bobbin Thread Tension
MORE TENSION
LESS TENSION
Fig.26. Regulating Needle Threod Tension