[PSUBS-MAILIST] fiberglass shell

Wed Aug 12 17:48:45 EDT 2020

Brian, four ft dia is a big cone. My suggestion would be to cut a plug out
of styrofoam with a hot wire. Once rough sanded, skim coat with drywall mud
and finish sand. Seal with Famwood Glaze Coat epoxy. Coat with a mold
release agent and then layup a few layers of fiberglass to create the mold,
then pull your part from the mold as usual. Should require minimal  finish
work when complete. I will be doing this method in the next couple of weeks
on a number of parts on the SeaQuestor.
<https://www.google.com/shopping/product/2218908236661412942?client=firefox-b-1-d&biw=1536&bih=732&sxsrf=ALeKk00jVHGImFc7d1zoPp9a7X5UYH7agg:1597268543519&q=home+depot+epoxy&oq=home+depot+epoxy&gs_lcp=Cgtwcm9kdWN0cy1jYxADMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADICCAAyAggAMgIIADoECCMQJzoECAAQGDoGCAAQCBAeUO7iAVjz7gFg2PQBaABwAHgAgAFOiAGTA5IBATaYAQCgAQGqAQ9wcm9kdWN0cy1jYy13aXrAAQE&sclient=products-cc&uact=5&prds=epd:12209065553474892030,prmr:1&sa=X&ved=0ahUKEwiHr9SQ0ZbrAhWRsJ4KHRbcBhcQ2CkI5gU>
Best Regards,
David Colombo

804 College Ave
Santa Rosa, CA. 95404
(707) 536-1424
www.SeaQuestor.com

On Wed, Aug 12, 2020 at 7:08 AM Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Ian, Alan,  Thanks for your observations !    the cone I have to make will
> have to be pretty large , like around 4' in diameter .  It be easier to do
> a straight hemisphere but I was thinking more of a elongated cone shape .
> I'll have to play around with some parabolic shapes.   Yes I guess I've
> been looking at too many of Hank's videos, but I would like to keep the
> expense down .  Seems like a hole in the ground would be pretty cheap, I
> could get a couple of hombre's to dig the hole for me , and maybe get a
> plastering person to do the form as well.  I spent so much time on my
> previous mold it was just insane, so many steps !
>
> Brian
>
>
>
>
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Ian Juby via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] fiberglass shell
> Date: Wed, 12 Aug 2020 09:45:29 -0400
>
> Hi Brian,
> I've done a lot of working with (and sculpting with) plaster of paris - I
> love the stuff, but think you'll find it just makes a mess in this case
> because the surface will be near impossible to finish properly. Partly
> because of the size of area you need to work really, really fast just as
> it's setting up. How big does the cone need to be? And can it be spherical
> or does it have to be cone shaped?
> If I may suggest, a good old dollar store beachball or sports ball makes
> an excellent mold. You can inflate it to the right size, and then plaster
> that and put plastered burlap on the outside of the plaster to hold its
> shape. Simply deflate the ball to remove it, and now you have a nice, even,
> smooth finish plaster mold which will be much more easy to release your
> fiberglass from. And your fiberglass winds up with a super nice, smooth
> finish.
> Further to that, but along the same idea, you can get tons of cheap,
> inflatable pool toys that may have a cone shape you can use as well if you
> need a cone shape.
> Just be aware that pressure changes will occur in the inflatable because
> of temperature variations. Namely, plaster will both heat up the ball and
> the air in the ball, and so the ball will expand. This was a fatal problem
> for me because I was trying to make a huge globe, so I either had to make
> it in two halves (and the halves would invariably wind up different sizes
> because of the variable expansion of the ball as a mold) or make one sealed
> sphere, which both trapped in the heat and the outward pressure of the air
> expanding inside the ball would stress the plaster mold and crack it. I had
> to have tolerances that were too tight so the two halves would match to
> make a sphere. But in your case, I suspect you have some tolerance and room
> for error on the size of the cone/sphere? So that shouldn't be a problem
> for you then.
> Do you have access to a wood lathe? Can you turn a stryrofoam blank and
> produce a mold from that? Or apply the fiberglass straight to the
> styrofoam? Sculpting fiberglas and getting a decent finish is a pain.
> You've got the right idea to make a mold in which to cast the cone - that's
> the best way.
> For what it's worth, here's one short article on sculpting a fiberglass
> nose cone:
> https://www.apogeerockets.com/education/downloads/Newsletter413.pdf
> But by far and away, the best thing is to start with something cone-shaped
> and the right size already.
> Oh - if you can get away with a sphere, you can blow-mold a sphere as
> well.
>
> Ian
>
> On Wed, Aug 12, 2020 at 12:32 AM Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Alan,   I could coat the plaster of paris with resin and then polish that
> really well , then apply mold release to that , then shoot gel coat over
> the mold release , then fiberglass and resin over the gel coat.  I would
> bury some sort of lever underneath the cone so I could pry it out of the
> ground.
>
> Brian
>
>
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] fiberglass shell
> Date: Wed, 12 Aug 2020 16:24:28 +1200
>
> Hi Brian,
> I am hearing alarm bells. The plaster of Paris will have to be pretty dry
> & any
> resin from your fibreglassing would suck in to it unless you gave it
> several coats
> of shellac first then put on a mould release wax. This is from memory from
> a long
> time ago. Also I have vague memories of coating polystyrene with pva glue
> which
> doesn't dissolve the polystyrene, & fibreglassing on to that.
> Will take a big block of polystyrene.
> Alan
>
> On 12/08/2020, at 3:14 PM, Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Hi All,
>                I"m thinking of doing a fiberglass nose cone for the front
> of my sub which will have flotation foam in the top part of it.  This time
> rather than make a whole mold assembly I was thinking I would dig a large
> hole in the shape of the nose cone, use plaster to get it smooth and then
> just put fiberglass against the inside of the plaster.  Then lift the thing
> out and break off the plaster.
>
> Brian
>
>
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