From: Roger Kulp <[log in to unmask]>
> Mike,Do you have the actual patent that shows how these records were
> made?If so,I think we would all be very interested in seeing it. Roger
I haven't found the patent yet, but I had read it and actually the
technique is very easy. The cutting lathe has to be set for very wide
spacing. To do four grooves, if the cut is usually 100 threads per inch,
set it for 25. Then cut the first recording which would be much shorter
than usual, about a quarter of normal time. Then reset the stylus at
the outer edge but turn the master 1/4 turn. Then cut the second
groove. It will lay down right next to the first one but leave space
for the other two. Then set the cutter at the outer edge but turn the
master another quarter turn. After cutting the third groove, the fourth
groove can be cut in the remaining space by again turning the master a
quarter turn.
If you need just three grooves, set the spacing at 33 1/3 threads per
inch and turn the master a third of a turn for the next two cuts. The
patent has a neat line drawing that illustrates the master with the
letters a, b, and c at the start of each of the three grooves.
Mike Biel [log in to unmask]
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