----- Original Message -----
Sent: Thursday, December 08, 2005 5:10
PM
Subject: Re: [PSUBS-MAILIST] making
hemispheres [was "manipulator arms"]
rick
I know that making the mold is a pain but this sounds like a
great oportunity for the kids to get involved. I have had some good success
using low density foam for the fillers and have even used paper machey over
chicken wire before.
I assume you know that
fiberglass shrinks as it cures and can compress a male mold tight
espescially if you dont use enough pva or if you try to go orver 270 degrees
of radius. all of the nose cones that i build are two pieces then
joined for that reason
start with the bucking frames
for the support of the outer shell of the mold
I assume that you are trying a for true
hemisphere at this point if you are tyring for a modified shape like the k 350
fairing as long a the center line of the radus stays the same this
trick will still work. stuff the mold voids with anything untill you are about
a 1/4 inch shy of the inner surface of the fairing. i forgot to say to
make a radius block for the design shape with a mount point at the center of
the bucking blocks and the lower edge. now apply the expanding foam to
the out side. after hard trim to match radius block. apply a thin coat of
bondo to the surface to fill any voids and seal the surface. Fair the mold
again rember that we will only be using a little over half of the mold for
about 190 degrees of the radius. glass the mold using thin bi directional
cloth. fair again. apply the final coat of resin and do not touch anymore the
mold is done. remember that most of the material in this mold are flamable so
slow cure resins are prefered less you want a nice fire.
time to start on the fairing.
apply pva to the mold, be generous this is the release agent. after dry apply
the first coat of glass and continue to build to the desired thickness . matt
can be used but will require more fairing. caution low blushing resins or
laminating resins should be used at this point. or just dont stop untill all
layers are applied. with the dried fairng still on the mold mark for edge cuts
and final fair. remove from the mold trm edges and install any internal
supports as needed.
i know that this sounds like a
lot of work but it really is not.
the frames are just circles of
3/4 ply spaced about 12 inches apart with a dowel running up through the
center. fillers can be chicken wire and paper machey/ styrafoam basically any
thing that is light wieght and some what ridgid. expanding foam any hardware
store. bondo any auto paint store
rick m
----- Original Message -----
Sent: Tuesday, December 06, 2005 11:00
AM
Subject: Re: [PSUBS-MAILIST] making
hemispheres [was "manipulator arms"]
An idea I've considered is buying a large
exercise ball and inflating it till it was quite firm. I'd use that as
the male mould. Take the female off that one and use it every time I'd
need to rebuild the nosecone. Like when my obstacle avoidance
sonar failed.
Needless to say it wouldn't have any surface
patterns, ribs, seams, etc. At least I'd try to get a seamless
one. Less work later on to grind off funny lines and "made in China"
labels.
One consideration is that the ball would
probably not be to scale. Could possibly use only part of the arc of
the ball for the nosecone. That way the scantlings could be faired
into the cone.
Rick L.
Vancouver
----- Original Message -----
Sent: Sunday, December 04, 2005 3:37
AM
Subject: RE: [PSUBS-MAILIST]
manipulator arms
As a matter of fact Rick, check out Brian Lula's observatory
construction pics for ideas on your spherical mockup. Not that second
monster of his, but the first one he built in his yard.
http://www.heavensgloryobservatory.com/
Ahh...too many interests, not enough life to do it all!
Joe
From: "Joseph Perkel" <joeperkel@hotmail.com>
Reply-To:
personal_submersibles@psubs.org
To:
personal_submersibles@psubs.org
Subject: RE:
[PSUBS-MAILIST] manipulator arms
Date: Sun, 04 Dec 2005
02:49:49 +0000
Rick,
"Want to start the hull mockup but have
not yet figured out how the make a hemisphere form plywood
yet."
There are good hints about this within the
homebuilt astronomical observatory community.
Joe