"David Hare-Scott" writes:
No and I am by no means an expert on these things but I will have a guess.
The heavier line pulls harder due to centrifugal force and this is slowly
unreeling it, luckily at a useable rate. In any case bless the day that you

A centrifugal force can undoubtedly be identified here, but I discounted
it as being the principal factor accounting for the line playing out at
the perfect rate because, were it the principal factor, then it would seem
to lead to a run-away condition: the more line that unreels the faster it
would unreel until it hit the metal cutter and then it would keep on
unreeling and chopping off pieces until none remained! This does not
happen. Despite using it on vastly different areas of grass, varying
from sparse dry summer grass to thick wet buffallo, it continues to feed
out automatically, apparently, as needed and not to excess.

The spool rotates because a dozen teeth (*) on its underside mesh with a
dozen teeth on a plate on the shaft of the electric motor. The only way
it can play out more line is for the two sets of intermeshing teeth to
slide over each other by at least one-twelfth turn. Normally this is
brought about by tapping the head on the ground, causing the two sets
of teeth to separate. As I never tap it on the ground, the teeth must
be sliding under load. I've been anticipating they may all get ripped
off, but it hasn't happened yet. Touch wood!

The limited pressure of the flimsy spring that presses the teeth on the
spool onto the toothed drive plate must be allowing slippage, but not
to excess, otherwise I would hear the change of sound as the metal cutter
came into play to trim off the excess line.

(*) there's probably a better term than "teeth" but none springs to
mind ATM
--
John Savage (my news address is not valid for email)