Brother FAX-170 Service Manual page 20

The cutter gear (Q) is a two-stepped gear whose inside gear is a one-tooth sector gear.
While the cutter gear (Q) rotates by one turn for one stroke of the upper blade of the cutter,
the one-tooth sector gear slightly turns the platen gear (H) clockwise via the reverse gear (I)
to feed the recording paper back into the equipment. This prevents the upper blade of the
cutter from scratching the leading edge of the remaining paper.
One-tooth sector gear
I (Reverse gear)
Q (Cutter gear)
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