[PSUBS-MAILIST] Fiberglass

Mon May 4 17:14:23 EDT 2015

Alan,
Tacky means weak hardener ratio or poor mix.  Tricky stuff!
Hank--------------------------------------------
On Mon, 5/4/15, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] Fiberglass
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Monday, May 4, 2015, 5:11 PM

 Hi
 Alan,
 Interesting comment
 about the polyester being designed for one shot. The
 polyester resin I used is from 3M and the instructions say
 that it you restart the job on a cured layer you should sand
 it lightly first - so that's what I did, since it took
 about a month to get the desired number of layers on. It
 didn't seem to have any bonding issues with layers
 applied on cured material. This particular 3M polyester
 cures fully in 2 hours, and didn't feel tacky after
 that, so perhaps this is brand specific.   
 Good point about the sections
 helping make the mirror versions of the MBTs. I made
 templates out of thin particle board to cut out the foam
 sections, and by flipping the templates was able to make
 mirror image tanks. 

 Best,

 Alec
 On Mon, May 4, 2015 at 4:33
 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:
 Hi
 Scott,some great ideas
 from Alec there.I like his
 idea of using sandwiches of thinner sheets of
 polystyrene.You should be
 able to trace a shape on one sheet, cut it out,
 thencopy around it on to
 the corresponding sheet of the mirror imageballast tank, to get two tanks that are
 identical.When I did mine
 I marked the hull with a felt pen as to where
 theballast tank was going
 to fit against it. I covered this area with
 plasticfood wrap. I then
 draped glass mat over it & epoxied about 3
 layers over this. Polyester resin will
 disolve the plastic food wrap. This approach may be a
 problemon vertical walls & there
 may be a similar appoach that works better.You need to embed this shape in to the polystyrene
 section by wire brushingout the
 polystyrene untill it's a good fit. Because of shrinkage
 of the fiberglass& warping it
 won't nessecarily be a perfect match & may require
 additional work.Once you have the
 polystyrene shape done you cover it with fiberglass & go
 overthe area you formed against the
 hull.I used epoxy because it can go
 straight on to the polystyrene (test it first)
 &you can spend a month slowly
 building it up, whereas polyester resin is
 designedto be laminated in one shot. It
 is air inhibited & remains tacky on the outersurface unless it has a wax additive.I once made a 1/4 size ambulance out of
 polystyrene using mainly achain saw.
 Great fun but one hell of a mess.Alan

 From: Alec
 Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
  To: Personal
 Submersibles General Discussion <personal_submersibles at psubs.org>

  Sent: Tuesday, May 5,
 2015 3:33 AM
  Subject: Re:
 [PSUBS-MAILIST] Fiberglass

 Hi Scott,
 Coincidentally your timing is really
 good, because I just finished four rather complex-shaped
 MBTs for the new sub. Since my sub is a one-off rather than
 a series production item, I used the method of glassing foam
 plugs that are then dissolved, rather than making molds. To
 summarize:
 - The plugs
 are a sandwich of many layers of pink home insulation foam
 from HomeDepot. When I did Snoopy's saddle tanks I cut
 out the sections with a hot wire, but this time I realized
 my jig saw does the job in about a tenth the time. Step one
 is to cut a whole bunch of sections and glue them together.
 If I weren't so tight-fisted, the ideal solution here
 would be to mill a single block of foam using CNC equipment,
 but I get by with what I have on hand if it'll save
 money - and a milling job would probably take quite a lot of
 it.
 - The glued
 sections are only a rough draft of the final form. Next you
 have to shape them until the steps between sections are gone
 and everything is nice and smooth. I use three tools to go
 from the draft to the final product, in this
 order:1) A plain old wood saw2) A
 Stanley Surform shaver, with flat and or rounded blade
 fitted depending on the surface. This thing is absolutely
 essential and I use it for 99% of the job. See http://www.stanleytools.com/default.asp?CATEGORY=SURFORM+TOOLS+AND+BLADES&TYPE=PRODUCT&PARTNUMBER=21-296&SDesc=Surform%26%23174%3B+Plane+Type+%96+Regular+Cut+Blade3)
 Sand paper
 I'm
 afraid I have no scientific answer to ensuring symmetry. I
 just put the plugs side by side and do a bunch walking in
 circles, taking measurements, and using a level. The plugs
 won't come out identical, but close enough to be
 functional. This part is more sculpture than
 science.
 - Next, paint
 the plugs with several coats of water-based paint. This is
 to prevent the resin from dissolving them. Water-based
 because if not you run the risk of the paint dissolving the
 foam.
 - Now apply
 layer after layer of wetted fiberglass cloth. I don't
 mean all in one sitting, I mean iteratively for about a
 month. There are two main considerations then, cloth and
 resin.
 I can't
 give you a specific recipe for cloth or the cost for cloth,
 because I used a combination of material I already had on
 hand and new stuff. I have purchased from http://www.fibreglast.com
 in the past, but this time found lower prices on eBay for
 what turned out to be perfectly good material. Mostly I used
 6.5 oz (quite light) cloth so that it would drape better,
 but that depends on the shape of your tanks. For instance,
 on the inside face that goes against the hull, you can get
 away with much heavier material since its a gentle curve in
 just one plane, and the same goes for any flat surfaces. But
 if you have compound curves or tight curves its way more
 challenging to drape cloth without forming air bubbles. I
 make the walls that go against the hull thinner, since they
 aren't going to be banging against things like the outer
 or upper faces will. On average I probably put down ten to
 fifteen layers of cloth. The pros use vacuum bagging to
 prevent bubbles. With my caveman fiberglass skills I just
 try to avoid them in the first place by selecting
 better-draping cloth, and when I get a bubble I remove it
 with a flap wheel before putting down the next layer. In the
 middle of my layup I put down several layers of Kevlar. This
 material is trickier to work with than fiberglass, it
 can't be sanded and once cured you can only really go
 through it with carbide tools. The idea is to increase
 survivability by making the MBTs puncture resistant. If I
 hit a rock or a dock I still expect the resin might crack,
 but it should be quite hard to put a hole in the Kevlar. You
 might think this hard layer should go on the outside, but I
 put it mid-schedule so I could sand imperfections out of the
 fiberglass layers above it. 
 This job (new sub, not Snoopy's
 tanks) took ten gallons of resin. Everyone will tell you
 epoxy is stronger than polyester resin. However, epoxy is
 $76 per gallon vs. $34 for polyester, and Snoopy's
 polyester tanks have held up perfectly well for years. So,
 for me, this is a case of cheaper-is-sufficient and I went
 with polyester.
 -
 Iteratively sand and fix imperfections with a fairing
 compound. I used West Marine's #410 fairing filler (http://www.westmarine.com/buy/west-system---410-microlight-filler--P004_120_004_016).
 You can do this with Bondo as well, but #410 is easier to
 sand.
 - Dissolve the
 plugs. When I made Snoopy's saddle tanks the pink foam
 dissolved instantly with gasoline. This time, despite being
 the same brand foam it was somehow gasoline resistant, but
 acetone did the job.  

 Best,
 Alec
 On
 Mon, May 4, 2015 at 9:22 AM, via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:

 Alec,

 I was curious if you could go into details about the
 making of your saddle tanks?

 *Where did you get the foam and fiberglass and what
 types did you use
 *How did you shape the foam to ensure symmetry 
 *Was there any difficulty or anything you would do
 differently

 Thanks,
 Scott Waters

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