From: Brett Buck <buckbw@pacbell.net>
Subject: Re: building techniques
Date: 09 Mar 1999
Newsgroups: rec.models.rockets

"Jeffrey D. Gortatowsky" wrote:
>
> I've done some damn fine fillets if I do say so myself. Regardless of
> what glue I use the technique is the same.

   Glue for fillets?   I think a better choice might be SIG Epoxolite or
PGM&W Aeropoxy. Both are filled, slow-setting thixotropic epoxies that
are very strong and very easy to work with. They make beautiful and very
strong fillets. Neither is particularly sandable, but its easy enough to
get them perfect before they set that it really doesn't become an issue.
They will not flow, so its possible to use a rigid filleting tool of
appropriate radius to set the basic shape, let it set up partially, and
then smooth the surface with a water-dipped finger. Done correctly, it
needs no further prep.

    Aeropoxy is lighter and a little easier to sand, and probably
weaker. Epoxolite is very difficult to sand and very, very strong. The
big difference is the price - Aeropoxy is $14 for a 1.5 lb set, which is
a huge amount. Epoxolite is about $10 for an 8 oz set (16 oz total
volume).

    For application, a SIG glue gun or other syringe with the tip cut
off to a decent size is the way to go. The main trick is to not get it
slopped all over the place. I use masking tape at the edge of the
desired fillet radius, do the initial forming for the fillet, and then
remove the tape and feather the edges. Let it sit until it begins
getting stiff (about 20 minutes for Epoxolite), then glaze the surface
with a finger dipped in water.

     I've used this on both rockets and stunt plane fillets and it's
really the only way to go.

    I've tried an even lighter fillet system used by some of my toy
airplane buddies - Model Magic filler with thin CyA as a surfacing
agent. This seems to have potential. Apply it very sloppily (since it's
very difficult to wet-form), sand it to shape, then dribble on thin CyA
and buff it *very briskly* out with a paper towel. I haven't mastered
this yet, but the ones I haven't screwed up came out looking great and
very, very light. It can't be as strong as epoxolite or aeropoxy, but
ince in place it seems pretty durable.


     Brett