Another method for repairing badly damaged threads in wood is by using
epoxy with a filler.  Used in the marine world and indeed is used as
the initial thread where a strong and well anchored thread is needed.
Can be used in place of a cross grain plug.

Drill out the screw hole to a diameter less than the screw head and
a little deeper than the screw.  Clean up the screw then, holding the
head with pliers, drop wax from a candle onto the thread.  Now hold the
candle under the screw to spread the wax and leave only a thin layer.

Fill the hole with an epoxy plus filler (fine saw dust may work) mix.
The level will drop in a minute or two as it soaks into the wood.  The
screw will be pushed into the epoxy so ideally the epoxy should not
spill over.  Use West System epoxy or in Australia we have Bote-Cote
as well.

Place adhesive tape over the underside of the hole in the part to be
fixed to prevent epoxy adhering.  Push the screw through the tape,
assemble and secure using more tape or clamps.  When cured the screw
can be unscrewed and tape removed.

I've read that a stubborn screw can be removed by heating to soften the
epoxy using soldering iron held to the screw head.

Graeme Krigsman
Melbourne, Australia