Singer 620 - Trouble-Shooting Guide; Chainstitch Adjustments; Machine Settings for Chainstitch; Chainstitch Throat Plate Checks

TROUBLE-SHOOTING GUIDE
Chainstitch Adjustments
If sewing defects are encountered in chainstitch-
ing, the procedure given below should be followed
in adjusting the machine. After each step, check
the chainstitching operation. If the machine sews
satisfactorily, no further adjustment is needed; if
the machine does not chainstitch properly, proceed
to the next step.
Machine Settings
Check the machine to be sure it has been set
for chainstitching in accordance with the instruction
book; use 50 mercerized cotton or “A" silk thread,
size 14 needle, between 8 and 12 stitches per inch.
Check chainstitch performance.
Chainstitch Throat Plate
Check loop-retainer bar for free action; i. e., the
bar should move front to back with no binds. In the
front position, the bar should extend approximately
3/32 inch beyond the edge of the throat plate.
Check chainstitch performance.
When the bar is depressed against the throat plate,
there should be visible clearance (approximately
0.010 inch) under the rivet head. The bar should also
soring 3cc:< into oosition when ’he pressure is re-
iecsea. Check chainstitch performance.
Check ‘he alercea ‘co in -he car -or :narc eases
cr burrs. Chec;< c.nainsnrch cer-cr-nc nce.
Machine Adjustments
Check the radial setting of the bobbin case as
instructed on pages 15 and 16, Service Manual for
Class 600 and 603 Machines. The setting should be
to the center, or to the right hand side of the needle.
If radial setting is to the center of the needle, move
it slightly to the right hand side. Check chainstitch
performance.
Genrly raise or lower the pull-off finger, by form¬
ing up or aown until the finger is as close to the top
of the hook as possible but still maintaining thread
space. Check chainstitch performance.
CAUTION: Do not burr or nick the thread-handling
edges of the pull-off finger during forming.
Check for thread clearance in a 12-stitch-
per-inch setting by rotating machine by
hand. If thread clearance is sufficient,
perform normal stitching test.
_
21