[Noisebridge-discuss] Laser cutter : The Lens, the Lens!

[Martin Bogomolni]

Yesterday I showed Rob how to clean the laser cutter, align the laser
path, and how to clean the laser lens optics correctly to prevent
damaging them.  While doing so, I noticed the laser's lens in the
carrier is chipped.   I wish I had thought to take a photo and post it
while the lens was out of the carrier.

It's important to note that infrared wavelength mirrors are _not_ made
of glass.   This class of lenses are made of ZnSe (Zinc Selenium) and
they are about as soft as a fingernail.   You cannot put any sharp
pressure on these lenses, aluminum (and even dust) will scratch the
lenses, and you can snap one trivially in half in your fingers.   They
are truly remarkable optics, and often gold coated.

In any case, when assembling the lens holder there should have been a
silicone O-ring or soft spacer that prevents the aluminum from
directly contacting the top of the lens.  This is not the case (and it
may have come from Full Spectrum that way... they aren't known for
doing the best job of assembly) so the top of the lens has a circular
scratch, along with the chip on the side of the lens.

The chip isn't in the field of view for the focus, so this lens is
working -just fine- for now, and doesn't need immediate replacement.
That said, I think due to the chip on the side, and the compromised
top of the lens, that it will eventually crack or shatter on it's own.
  I recommend that NoiseBridge purchase a backup lens and keep it on
hand, to prevent a long-ish future downtime on the laser.

Replacement lenses are available from Full Spectrum laser for $250,
and if you need to buy the lens from eBay you'll spend about $60 +
shipping.  You should look for listings like "Dia 12mm ZnSe Focal Lens
f CO2 10600nm 1.06um Laser Engraver Cutter Focus 63.5mm"

-M