Table 3-1. Operator troubleshooting - continued
TEST OR INSPECTION
DARNING SEWING MACHINE
Step 6. Check for sharp, rough, or burred edges on rotary-sewing hook, bobbin case, or tension
If defective parts are found, notify next higher level of maintenance.
Step 7. Check thread size against needle size, variety, and class.
Be sure you have selected the rightthread weight for the needle being used (It may
be too heavy).
If the wrong thread is being used, remove thread and rethread machine with the
correct weight thread.
Step 8. Check that thread is left-twist thread.
If thread is right-twist thread, remove thread and replace with left-twist thread.
Rethread machine (para. 2-12c).
Step 9. Check that thread being used is not damp, old, or dried out.
Discard damp, old, or dried out thread. Rethread machine with fresh, dry, smooth,
left-twist thread of the correct weight (para. 2-12c).
BOBBIN THREAD BREAKS.
Step 1. Check that bobbin case is threaded correctly and installed correctly.
Thread and install bobbin case correctly (paras. 2-12d through 2-12g).
Step 2. Check bobbin to see that it is not so full of thread as to keep it from revolving freely in the
Remove excess thread until rounds of thread are even with the rim of the bobbin
Step 3. Check that rounds of thread on bobbin are not lapped over one another and check that
rounds of thread are evenly wound across the bobbin (no ridges or valleys in the rounds).
Use a correctly wound bobbin, or remove thread and rewind bobbin correctly with
proper thread (paras. 2-12d through 2-12g).