Re: [ATM] Invar and machines

["lafotec" <lafotec@thewaynet.com.br>]

----- Original Message ----- 
From: "dezrteagle" <dezrteagle@cox.net>
To: <atm@atmlist.net>
Sent: Tuesday, November 02, 2004 6:01 AM
Subject: [ATM] Schmidt Camera Quandries


Hi Jim:

Here in Brazil it's the same. I have troubles trying to get some special
steels like AISI 440C and Invar stock. Villares Steel makes these, they are
in their catalogue, but to purchase you must pay for a full 3 tons furnace
charge, so there is only one steel vendor that sells these, and of course,
pieces are expensive and limited to some gages.
For not so wear resistance, AISI 420  can be used instead, but for Invar,
it's a different matter. Here there is no substitute at all. Epoxy Graphite
here is prohibited to civilians, since last year, when "government new
orders" (idiots) iniciated a "gun and hazardous material ban program". Now
only industry can get epoxy/graphite componds, Kevlar and so.
Non CNC lathes and mills are fine to us ATMs, except some chinese machines,
that haven't good bearings and are bad built, wearing fast and don't be able
to keep tight tolerances. Old and used machines, like Hardinges, Myfords,
South Bends, Emco Unimats, Schaublins and so, are much better than that
brand new  "Charlies".
Laercio.



Well, new to the list, but not to pushing glass. However I've embarked on a
trip into new territory: building my own (and first) Schmidt camera. I've
just finished an 8" f/2.2 primary for the camera, but have run across some
kinks in the rest of my plans. First, does ANYBODY know of a vendor who WILL
supply a small quatity of Invar 36 (for the skeleton) and won't hang up on
me when they find out I'm not NASA? My local metal haunts here in Phoenix
are: don't have it, can't order it, forget it! I've tried going the way of a
substitute (i.e. epoxy-graphite), same results. Second, paging through my
copy of Telescope Optics (thank you Rutten&Venrooij), the idea of flattening
the field with a Plano-Convex lens really caught my attention. My interest
stems from the amount of time that might be saved following this path, from
what I've been able to gather, the process of machining the film holders is
very time consuming (correct me if I'm wrong). Has anybody tried this? I
have a metal lathe and end mill, niether of which is CNC capable. If footing
the cost of half a dozen lens and a few hours at the old lathe and drill
press can give me a faster result, so be it! Many Thanks, counting on any
help!
Thanx-Jim
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