From: Aplanatic{at}aol.com
To: atm{at}shore.net
Reply-To: Aplanatic{at}aol.com


Hi Scott,

I've made three carbon-fiber tubes for various applications including a low
thermal expansion tube for a Schmidt camera.

If you require a low TCE tube you must use as little epoxy as possible,
otherwise the process is very similar to making a fiberglass tube.  I don't
think there's a compelling reason to use carbon fiber for an OTA unless the
TCE is of concern.  If it is, then vacuum bagging would be a good idea to
reduce the epoxy content as much as possible.  I've never used vacuum
bagging and my best tube has a measured TCE of 8 ppm/C.

I've purchased the materials for the tubes from these folks:

http://www.acp-composites.com/acp-sbwf.htm

Their prices are reasonable.

To make a tube I first build a form using plywood disks spaced about
8" apart. The plywood disks are center supported on a 2" diameter
aluminum tube.  I then wrap the plywood disks with a single layer of 10 mil
plastic sheet.

Be warned that it's quite an undertaking especially for a large tube.  You
can find a lot more info on tube construction methods in the archives from
Dave Pitou and others.  These archived posts deal with the layering
structure, foam and hexcell cores, etc.

-Dave Rowe-

> Anyone have experience with fabricating carbon fiber telescope tubes? My
> usual method of wooden construction is going to be too heavy for what I
> am trying to build currently. I am thinking I need a vacuum
> bagging
> setup to make it work. Anyone have any tips?

--- BBBS/NT v4.00 MP