Thank you everyone, for your comments on cutting surfaces and tools.
As it happens my wife, Beryl, is a keen patchworker and I have had an
eye on her circular fabric cutting knife for some time.  The trick will
be to sneak it away when she's not looking.

About two weeks ago she came back from a trip to the patchwork shop and
said "They had these special plastic cutting mats on special at $5 each,
so I bought a couple for my girlfriends.  Do you want to see if they
fit your roll repair thing?"  I took one down to the basement and was
staggered to discover it was _exactly_ the right length (to within a
millimetre) for my repair table and was usefully wider than a roll.
Should I decide to start using Terry Smythe's technique of trimming
along the edges this mat will be ideal.

BUT --- I'm still worried about the tape adhesive right at the edges
of the roll causing successive turns of the roll to stick together.
I suppose no comments on that means no one has had any really bad
experiences of that nature.  All the same, I'm going to proceed very
carefully.

Yes, Terry, I will try to make some photos of the roll table available.
This may take a week or three because most people take some summer
holidays here in Australia just after Christmas, and I'm going to need
some help. But it will be done eventually.

John Phillips.