----- 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