In MMD 010608 Pete Knobloch wrote:

> They are developing a scanner using 300 DPI technology that is more
> accurate than any of the old pneumatic systems are capable of.

Even if accuracy of the reading (scanning) technology were infinitely
fine, we'd still be in the same position.  We're talking about a
mechanical perforator, with discrete coarse-grained punch sizes and
step rates, not a laser cutter with an infinitely fine punch size and
infinitely adjustable step rates.  Either the leading punch or the
trailing punch will present problems.

Let's assume that the original slot was _about_ 1 inch long (we really
don't know because the original rolls either swelled or shrunk over the
years), and an original punch die that was _about_ 1/4 inch wide
(because we don't know if the machine had been well maintained when the
roll was cut).

Now that you think you know what is supposed to be the correct length,
you can adjust the perforator to stop punching ... when?  Just before
entering the last 1/4 inch of the original slot?  Just after?  By how
much?  What's the fudge factor?  When do you _start?_  Just after
entering the first 1/4 inch?  Just before?  What's the fudge factor?

Get this part wrong, and the slot will be 1/4 inch too long or too
short.  Even worse, it may be too early or late by 1/4 inch.  Does this
fudge factor remain constant over the whole scan?  Are you going to
make this fudge adjustment for each and every slot?

Okay, so we'll go for micrometer step rates.  Oops, we're still using a
1/4 inch punch -- the problem didn't go away, it just happen more often
now.  Okay, so we'll use a very thin punch.  How thin?  If it's razor
thin, then what's the maintenance cost of keeping it sharp enough?
Will it last through one whole role?  Or two, or ten?

What a mess.  Experience tells us that if it's getting this complicated,
then we're going down the wrong rabbit hole.

Now let's assume that we _know_ -- because we went to the trouble to
research, calculate and find out -- that the correct slot size is 8
punches with a punch size of 1/4 inch and a step rate of 1/8 inch.  Now
there is no guessing (no fudging).  Punch 8 holes, 1/8 inch apart, with
a 1/4 inch punch.  Done.  Perfect match.  The precise length in inches
or millimeters or Angstroms of the original particular slot is
irrelevant.  Suddenly the complexity goes away.  It's conceptually
simple, and mechanically simple.  That's how you get accuracy at a
competitive price.

This is what Dave Saul and Wayne Stahnke do.  Wayne's method determines
that the slot is 8 holes, with a 1/4 inch punch and a step rate of 1/8
inch.  He creates a computer data file that says precisely that.
Dave's perforator reads this data file, and cuts the roll as 8 punches,
with a 1/4 inch punch and a step rate of 1/8 inch.  Done.  Perfect
match.  At a competitive price.

George Bogatko
http://www.inluxeditions.com/

P.S. -- Please don't bring up projects to use laser cutters to recut
rolls.  It may be accurate, but you'd be paying about $100 per recut.
Besides, it isn't necessary to go that way.  This would be like buying
an IBM mainframe computer to process your shopping list.