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Re: [PSUBS-MAILIST] making hemispheres



rick
about have an hour with a long board will do it.if you are talking about the mold
the fairing on will depend if you used matt or cloth and what type or fairing compuond you used. i would not use bondo underwater one of the west system fillers is probably the best for this,
 
rick m
 
----- Original Message -----
Sent: Thursday, December 08, 2005 9:34 PM
Subject: Re: [PSUBS-MAILIST] making hemispheres

Hi - hey, thanks for the great rundown on the nosecone glassing.  This goes into my keeper file.
 
I admit it wasn't quite the project I was looking forward to.  You mentioned it's not really that big a deal.  One concern I do have is the final fairing process.  I imagine that for the final smoothness you're using a vibrating sander of some sort over the bondo?  Or is it a hand-sand all the way . . .
 
So many finished fibreglass products I've seen are absolutely perfect - I'm used to looking at boats and aircraft.  There must be hours of, um, suffering involved here?
 
Rick L
----- 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