RE: [ATM] "Render Unto Ceasar. . . . "

[artbianconi@blast.net]

Absolutely! I got the recipe for it from Stephen Hawking while he 
and I were lifting weights at the gym!

You realize of course, you've ruined everything. Now I must wake 
up before writing!

Of course it's 3 to 12 pounds per cubic foot!

Thanks for the heads-up

Art



On 26 May 2004 at 15:15, Royston_Jeremy@emc.com wrote:

Hello Art,
 Are you sure about the density of 3 to 12 lbs per cubic inch? 
Even
lead only has a density of about 0.43 lbs/cubic inch

Jerry

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-
bounces@atmlist.net] On
Behalf Of artbianconi@blast.net Sent: Mittwoch, 26. Mai 2004 
15:09 To:
Daniel Fundo Cc: atm@atmlist.net Subject: Re: [ATM] "Render 
Unto
Ceasar. . . . "


Back in the sixties there was a popular foam core material whose
chemical origins I do not recall but which was referred to as Clark
Foam. It was said to be made in Europe but I could not verify 
that. It
was available in an assortment of densities from 3 to 12 lbs per 
cubic
inch and in various sheet thicknesses starting at 1/4 inch.

Clark foam, at least as a descriptive name, has disappeared from 
the
lexicon of today's composite enthusiasts but there are still many,
many alternative materials that can coexist with a wide variety of
resin systems without desolving.

You can get a free catalog from Aircraft Spruce by going to their 
web
site but, when it comes to tech specs, scope of materials, tech
support I prefer one group for composite materials: Fiberglast. 
They
too have a web site. 

Core material can be just about any low density substance. The 
best, of course continues to be the oldest of the bunch: Dupont's
honeycomb but the cost is prohibitive and it resists bending 
around
very tight radii.

The most friendly, in my opinion, and most suited to OTA's is a 
low density foam core that is cut into small squares and held 
together with a fabric scrim. It's much the same method used for
holding small  bathroom tiles together (like you use for making 
mirror
tools).

It's perfect for wrapping around a mandrel when making a tube.. 
Depending on size and thickness, it will impart a slight prismatic
effect to the glass unless you sand it lightly beforehand. It does
however, create an exceptionally stiff part and does offer a 
modicum
of compression resistance to threaded fasteners, something low 
density
foam cores lack.

I personally prefer end grain balsa as a core material, especially 
in
areas where stress concentrations are likely such as the primary 
cell
attachments, the attach points for the EQ mount and perhaps 
the
focuser.

The most fun, however, is to be had when you uncover 
something that's common but not normally considered for this 
application. 3M, for example makes a red insulation material that
comes in a roll about 30 feet long. It's about 6 inches wide and
perhaps 3/8 inches thick. It's in the building department at 
Loews and
Home Depot. 

My first attempt to use it was a failure but only because I did not
use a microballoon mixture between it and the glass layup. I 
know
better but got lazy and the result was poor peel strength. 

These foams do not stand up to resin systems that employ an 
MEKP hardener. That's the hardener of choice for most 
Vinylester based mixes. Unfortunately, that the most likely to be
found in auto parts stores and Home Depot!

MEKP is dangerous! The fumes are highly toxic and the P in 
MEKP is for the Peroxide chemistry which will blind you should it
splatter into your eye. 

Safer polyester resin systems like West are not nearly as risky 
and will not desolve any of the foam cores. Even junk styrofoam 
can withstand it.

Good luck

Art Bianconi


On 25 May 2004 at 23:15, Daniel Fundo wrote:

<< I am finding numerous core materials that are equal to or 
better
than structural foam and less expensive. One thing is clear: there 
is
absolutely no excuse for the continued use of sono tubes for an
optical system.  >>

Art,  I agree......fiberboard tubes are too heavy.  I got hold of 
some
foam packing material that is phenominal  Its almost as light as 
high
density styro, but it's hard......takes a bit of pressure to put a
fingernail into it, but its still flexible.  I cut (with some
difficulty) some thin strips and laminated them with epoxy and 2 
oz
'glas.  The strips were rigid as hell and only weighed a few 
ounces.
Better than aluminum at the least.  Wish I could find out what 
the
foam board is called.  Just for kicks, I'd like to make a Dr.
Seuss-looking telescope......sort of an organic, free form, 
functional
sculpture.

*****-----
Dan F.


_______________________________________________
ATM mailing list http://www.atmlist.net/


_______________________________________________
ATM mailing list http://www.atmlist.net/