On 24 Sep 2006 02:28:05 -0700, "Lou" wrote:

Ok, I've made a few pieces to try out using 1/4" foam and fiberglass on
both sides. When I cut the pieces to shape with my band saw, small
strips (1/4" or so) seem to want to seperate. Is this common or did I
mix the epoxy wrong? The big parts are staying together, the fiberglass
itself is staying to gether but the small parts are seperating from the
foam.

Lou
I'm going to need to make some assumptions, so I'll start by assuming
that you are using epoxy such as the West System and that the foam is
the blue building material trade named Styrofoam. I'd suggest staying
away from the white foam or bead board which isn't nearly as strong.

Another assumption is substituting the word seal for prime. Typically
the foam is "sealed' with either a layer of epoxy, resin, or
microsphere or Q-cell mix (microspheres are mixed with the epoxy or
resin to reduce the weight, fill voids, and still give a good bond.)

Usually the microsphere mix works better than straight epoxy for
sealing the foam, but follow the directions for what ever you are
working on.

So... based on the above... I'll start out by saying I believe what
you are seeing is normal. I'll also note that small sandwiches of
fiberglass and foam are no where near as strong as pieces with larger
areas. I rarely see a sandwich made smaller than one inch and then
there are flanges of 3/4" to nearly 3" depending on the use.
The only pieces I've seen that didn't have a flange when they were
created were control surface ribs and bulkheads.

As far as cutting sandwiches, I cut oversize and sand to shape. As
Neal said, using the Dremel cut off rather than a band saw is a good
idea as are patience and a good dust mask. (not one of the little
fiber ones either)

NOTE the pages pointed to by the links below are relatively large with
lots of relatively small photos. A few of the photos in the
builder's diary link to larger versions. I'm using Vinyl Ester Resin,
but other than viscosity and cure time epoxy is going to work much the
same.

Control surface rib construction shown a bit over half way down on the
following page
http://www.rogerhalstead.com/G3_file.../glasair12.htm

Bulk head construction is shown about half way down the following page
with the bonding in place a bit farther down.
http://www.rogerhalstead.com/G3_file.../glasair10.htm

I'm guessing this problem is pretty much a function of size.
Small sandwiches with open edges are not strong until they have been
bonded into place. Both the ribs and bulkheads shown above are very
fragile until bonded into place and this foam is much stronger than
the blue Styrofoam (TM) Follow the instructions on what ever you are
building and good luck.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com