Re: ATM Aluminizing: diffusion pump obtained

["James Lerch" <jlerch1@tampabay.rr.com>]

Dominic,

Congrats on the Diff Pump!

Here's a couple of things I've learned over the last year or so, while mucking
about with my system.

#1 1/4" thick glass isn't thick enough for the low voltage / high current
electrical pass-thru for the filament power.  Last January mine cracked while
coating an optic.  (BTW, nothing exciting happened when it cracked, it just
started whistling air into the chamber.)  The best explanation of why it
cracked, that I can come up with, is the heat from the filaments worked its way
backwards to the bolt going thru the electrical pass-thru.  Since it was rather
chilly that day the glass was cold, and cracked from thermal shock.  I replaced
the 1/4" thick glass with a 3/4" thick piece, and no problems since then!

#2 Always evacuate the chamber before shutting down for the day, and store it at
low pressure. If stored at atmospheric pressure, moisture and oxides build up
and the next pump down will take substantially longer than normal!

#3 If you inadvertently cut your finger while clearing a path to the alluminizer
one day, DO NOT apply a petroleum jelly based anti-bacterial ointment to the
wound!  This is EVIL stuff to get in side a vacuum chamber!  The petroleum jelly
won't out-gas during pump-down.  It will happily hang around during the plasma
cleaning cycle. It will contentedly exist in a 2e-5 torr environment, but once
it see's vaporized aluminum it will produce a pressure spike like nothing I've
ever seen!  BTW, after you clean the chamber out with solvents, GO WASH ALL YOUR
HAND TOOLS, otherwise your doomed to repeat this miserable experience!

#4 No matter how larger your chamber, it won't be big enough :)

Finally, if anyone is interested, I'm currently building a 25" x 25" x 12" ID
chamber, and have some images of the project in this folder:
http://lerch.no-ip.com/atm/projects

Take Care,
James Lerch
http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site)

"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"