Happy HCS-1201-30, Maintenance Manual

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Adjustment of moving knife and fixed knife
3-6-8
1. Remove needle plate.
2. Check if knife drive shaft has no backlash in up and down
direction.
If backlash is found, adjust it referring to [3-6-6 Exchange
of moving knife].
3. Adjust slant of fixed knife with [upper adjustment screw]
and [lower adjustment screw] that fix fixed knife.
<Note> Rub these screws together to the extent that you
don’t feel resistance.
4. Cut thread and check how well it is cut.
Use two polyester threads for checking.
5. Check several times and if no mistakes are found, finish
this process.