-- forwarded message, please reply to sender and MMD --

Hi Robbie,  Happy New Year to you and all on MMD.  Here is my 2 cents
worth on the discussion on laser cutting and water cutting of music
rolls and music books.


Laser cutting

We run a CO2 gas laser cutter on plastics but it is 1000 watts, which
focuses into a spot diameter of 0.2 mm so the energy per square
millimeter pretty high.  When I show visitors the machine I tell them
how dangerous it is, and if you put your hand underneath the invisible
beam, even 250 mm away, it will cut your fingers off, which is bad news.
The good news is it cauterises the stumps so you don't bleed to death!

The laser is programmed by a computer aided design (CAD) program which
converts each cutting point to X, Y and Z co-ordinates.  The computer
drives high speed servo motors and lead screws to move the laser head
around the cutting area; in our case it is 4 metres x 3 metres x 1
metre up and down.

The actual laser beam can be switched on and off as required. The laser
beam is generated in a large cabinet full of gas-filled glass tubes and
electronics, and the beam is reflected by a series of mirrors to the
laser head about 2 metres away.  It is very similar to light reflection,
except the mirrors and lenses are designed for infrared wavelengths.
The lenses and mirrors are water cooled.

There are other lasers which work the same way but are smaller and
lower power, for cutting paper, model aircraft pieces, engraving
plastic, etc.  They don't need water cooling, and the solid state laser
itself may be mounted on the moving X-Y mechanical components and have
just the one lens.  They often don't need the vertical Z-axis motion.

The problems that are inherent in a laser are

1. speed: as the servos must move the head and it has some weight and
inertia to overcome.  We only get around 10 meters per minute cutting
speed.

2. spot diameter: we get around 0.2 mm, so to cut a hole, say, 1 mm
diameter we'd have to move the beam in a circle.

3. focus point: there is one focal point, as with a magnifying glass,
and above and below that point the beam widens.  Admittedly it doesn't
increase much in spot diameter over a few inches, but if you cut
through a number of thicknesses of material the hole diameter will be
different from the top sheet, through to the centre, to the bottom.

The lowest power laser that I'm aware of is 200 watts power and has
just a simple X-Y positioning table, being used for cutting balsa for
model aircraft.  The cost, second-hand, was $10,000 Australian.

Now, these are commercial prices and I'm sure a hobbyist could adapt
and make one off at a lower cost, but people often underestimate how
much it would really cost.  Also, even a 0.5 watt laser will destroy
eye tissue, so they are not something to take lightly.  We tune our
laser by melting holes in furnace bricks (it turns the brick into
glass!) and whilst doing this one day a technician accidentally burnt
his upper arm.  It didn't look too bad but it took six months to heal
because of the damage it does to tissue.

However, I think you hit the nail on the head when you questioned the
cost and difficulty of using a laser versus a simple electro-mechanical
punch mounted on the X-Y head.  All the mechanics are the same except
that, instead of the complication of the laser, you have a solenoid
punch with interchangeable punches to suit any hole size.


Water cutting

I also have some experience with water cutting machines.  These consist
of a very high pressure pump (up to 20,000 psi), pumping water through
high pressure piping to a nozzle with a tiny hole in a diamond or
tungsten carbide disk.  The amount of water used is so small that you
can't see it and paper would hardly get moist, although in continuous
use a mist of water vapour builds up and is usually exhausted via fans.

Mechanically, either the entire pump unit moves on the X-Y-Z axes or
the table moves under a fixed head.  As you can imagine, it is no minor
plumbing matter to contain water at 20,000 pounds per square inch
pressure.  There are safety concerns about high pressure water cutters,
for obvious reasons.

Again, one has to question whether it is worth all the hassle. If you
look at the punch machine of Le Ludion (refer post by Philippe Crasse,
99-12-23 MMD, No. 2) you will see they have an electromechanical punch
driven by a high speed screw servo in the Y axis, i.e., across the
paper.  The music paper is fed between rollers, driven and controlled
by another servo to give the X axis, i.e., end to end of the roll.  A
computer tells the X and Y servos where to move and also operates the
punch.

This is fast, accurate, simple and cheap (well, relatively cheap --
I'm sure Philippe can vouch for how expensive it was to do the job
properly!).  However, notice how this commercial machine is built to
high engineering standards, to ensure speed, accuracy and low
maintenance.

Bob Essex (see post in 991106 MMD) has a similar approach on a hobbyist
scale that would be practical for someone to make a few rolls at home,
but as illustrated it may suffer too much wear and tear if operated on
a commercial basis, as Le Ludion requires.

The suggestion that a light pen could run back and forth across an
original roll, whilst a laser cutter or water cutter or punch follows
on a new roll synchronised to the original, would also work but would
be slow.  As you point out, how fast would it have to move to cover
every 0.1 mm or so across a roll, for the entire length, to check if
there is the start of a hole?

Someone explained they have found an array of photocells adequate
to read different formats of rolls.  This is much faster and probably
cheaper than a mechanical method.  If it is impractical for one array to
cover a range of hole spaces, one could have several tracker bars with
holes at the correct spacing for the system, with light pipes back to
the photocells mounted at a convenient spacing.

There are sites on the internet for lasers and laser cutters, as well
as sites showing construction of X-Y tables with servos, construction
and operation of hobby robots, computer software, etc., all of which
might promote further ideas to solve the music roll problem.

Sorry if I pour cold water on the innovative ideas put forward and
I certainly hope I don't cause offence, but as an engineer I look at the
simplest, best and lowest cost ways of doing a job and unfortunately,
however neat they might be, I can't see lasers or water cutters being
practical.  A combination of simple electromechanical, electronics and
computer power would seem to be the current "best" way.

However, just imagine having a laser roll cutter at the next Mechanical
Music Exhibition:

 "And for my next trick, would a gentleman from the audience -- Yes you,
  sir, waving your hand -- would you like to stand right where you are
  while I perform the amazing 'cutting the hand in half trick.'"

Regards, Colin MacKinnon
Sydney, Australia

 [ See the photograph of the Le Ludion punching machine at
 [ http://www.leludion.com/pag_ludion/perfo_e.htm (English)
 [ or  http://www.leludion.com/pag_ludion/perfo.htm (French)
 [
 [ A better description is given in the French text, which I translate
 [ loosely as, "Regarding the restoration of the old cardboard music,
 [ our video camera records the images, processes them, we freeze the
 [ image at the monitor, and then we mark the holes on a new medium."
 [
 [ -- Robbie