Re: [PSUBS-MAILIST] Fiberglass Plug

Good Evening Dan,

I appreciate you taking the time to give use some good fabrication data to chew on. I'm lucky I have a good CAD program to be able to see a 3D mock up of a composite fairing when it is attached to the main hull. I can see from your description that it might be easier for me to go the cedar/pine strip canoe mock up route. Since I can make perfect symmetrical cross sections as close together as I like, I should be able to get a pretty good shape with not to much in the way of dips and humps to deal with. I can sand the wood surface with a DA sander and then cover the wood with a thin layer of fiberglass then sand that and then apply bondo. Once all that is smooth I can; primer, gel coat, mold wax, PVA mold release and start to make my mold. I have also had some trouble with the mold release agent. I was trying to make a mold of a glass head and I was brushing the PVA mold release agent onto the glass and it would just bead up like water on a ducks back. I figured I would need to wax the glass surface and then use a pot sprayer to apply the PVA mold release. I have not had time to get back to that project to I don't know if that will work or not. As you know if the PVA doesn't go on smooth the gel coat applied over top of it will reflect that. I've been told it's best to apply two good coats of PVA.

Some time back when I was thinking of a plug for a larger project, I was thinking about spackle ( or as I call it sheetrock mud) since it is very cost effective. I know how to use mud since I used to make a living applying it to every surface that came before me. : )'

Yesterday I was down at a local composite fabrication shop that makes pontoons for aircraft called Aerocet. They had an amazing system there that is leading edge. I spent a couple of hours talking with the owner and his lead CAD engineer and I'm still trying to unload all the data stored in my brain. They make there plugs first in 3D CAD models and then have them 5 axis CNC cut out of high density foam down a little below the final surface desired. Then they apply a thick layer of fiberglass composite and then once that is cured they CNC the fiberglass surface to the exact surface they desire. This is then covered in gel coat before a mold is made from it. I may be working for them in the near future.

The resin used doesn't eat the high density foam since it is a much different material then styrofoam. Doc, builder of the Bionic Dolphin, used latex house paint to cover one or more of his prototype styrofoam plug molds before he waxed them in preparation of making a mold off of them. I guess the latex paint doesn't eat the styrofoam. He also did a none working prototype and was able to cover the latex painted surface with fiberglass but he may of put a automotive primer over the latex paint first. I'll have to ask him. He started his mold plug with a large block of styrofoam and then drew top, bottom, and side profiles or which he could use a hot knife wire type cutter the get the rough shape.

http://www.bionicdolphin.org/tom/source/construction.html

http://www.bionicdolphin.com/cms/gallery/photo/index4.html

"Once I had the approximate size worked out I checked the volume my MBT would have and tweaked the shape some"

I can see how having a CAD model of your MBT's can make it easier to check your internal volume. Now days with all the people in the PSUB group that have CAD skill's a person should be reasonably be able to get some good data on a design there working on. I was thinking Dan, that if you still have your MBT molds for your version of the K-350, people might wish to hire you to make them a set of fiberglass tanks, like yours for there own K-350 project. Or some one could perhaps buy your molds or a copy of them so they could make there own and/or manufacture more for selling to other PSUBers, if your not interested in manufacturing them.

I still think it would be educational to see any pictures of you making your mold plugs if you come across any in the future.

Regards,

Brent

"The trouble with bucket seats is that not everybody has the same size bucket."

From: " Dan. H." <jumachine@comcast.net>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] Fiberglass Plug
Date: Wed, 31 Jan 2007 08:46:08 -0500

Brent,

The plug can be mocked up in many ways. I'm not familiar with 3D CAD but I imagine working it out on a computer and then making wafers of the plug and cutting them out of something would be about the easiest. If not CAD I know you can do the same with technical descriptive drafting. (Old School) But that's time consuming and you can't get a 3D feel on flat paper. Once you have wafers, of maybe half inch thick something, you could fill in or grind off the excess to form the smooth 3D shape. I kind of did that but didn't use anything so technical. I waited until I had my hull built to design my fiberglass so I could see it all in real life.

With my hull already built, I cut two shapes out of one inch Styrofoam, one for the X axis and one for the Y, taped them to the hull and walked around it reshaping until I was satisfied. Once I had the approximate size worked out I checked the volume my MBT would have and tweaked the shape some. Following this approximate shape I cut a stack of one inch thick Styrofoam pieces and glued them together with construction adhesive. My sheets of Styrofoam were stacked flat on the horizontal against the finished hull. Form there it was a matter of sanding off the sharp edges that were sticking out farther then the surface I wanted and then filling in the rest.

Actually I sanded the Styrofoam a bit smaller then what the finished plug would be so I was sure to cover it all with plaster.

Once my Styrofoam was to shape, I applied plaster of Paris to all the larger sunken cracks and crevices. Plaster of Paris doesn't shrink when it cures and cured to it's full depth fast. That was then sanded to shape or a bit below.

After that I started with spackling compound. Spackling compound sands easier then plaster of Paris so it's best if you remove any plaster that you think will be to high before applying the spackling compound. Also spackling compound cures slower and shrinks some. It's better to apply it thinner and more times then to thick and have it not cure to depth. With the spackling compound, it's a matter of applying even coats until the entire plug is coated with it. Apply enough so you can sand it to the finished shape.

Once you start block sending on it you'll find dips. You can apply a bit more to them and resand. It's a simple matter of applying spackling compound and sanding over and over until your happy with it. It's done exactly like a body man would does body work on a car, only the spackling sands much easier then body putty. Keep feeling with your hands and eyeing it up until all your curves are smooth with no roller coaster looking surfaces. If you think your getting out of shape, make some cardboard templates of one side and fit it to the opposite side to see if your curves match. Remember, you can't see both sides at the same time anyway so if it looks good to you as your studding it, it should look great to the casual observer late on. Be sure you have no Styrofoam showing through because the fiberglass resin will eat it away.

Once your happy with the plaster plug, give it several coats of wax to fill the finer sanding scratches and then mold release if you want to. If I remember correctly, I had a tough time applying the mold release to the waxed surface. Even if your mold stuck on the plug in some spots, you could just destroy the plug to get it all out.

You still have a second chance to repair small defects by working on the inside of your mold but it's tough working on the concave inside rather them on the convex outside of the plug, so get it as close as you can. Also, for durability, all repairs to your mold should be done with auto body filler.

When your satisfied with the mold, wax it and apply mold release, then the jell coat and lay up the glass. Even on the finished part it's not that difficult to repair spots with fiberglass resin body putty. You'll be painting the entire sub anyway. By now your body man skills should be pretty good!

I have a friend in the body shop business. He never did fiberglass plug and mold stuff but he was a great help in teaching me how to work on achieving the surface I wanted by feeling the imperfections and work them out.

There you have the long story. I hope it helps. The best teacher maybe trial and error. Take it slow and be observant as you go.

I'll look around to see if I have any more pictures.

Dan H.

----- Original Message -----

From: Brent Hartwig

To: personal_submersibles@psubs.org

Sent: Sunday, January 28, 2007 5:13 PM

Subject: Re: [PSUBS-MAILIST] Fiberglass Hull

Dan,

I've enjoyed seeing your custom fiberglass work on Persistence. I've been looking into different ways of producing mold plugs and was interested in how you made yours. I think I've seen most of the pictures of your sub available on the internet. How ever there is only one pic I've seen of one of the mold plugs you made up and I would love to see any other pictures of you forming the plugs if they are to be had. From what I know now if I were to try to make those plugs I would render section drawings with outside measurements from my CAD work onto transparency's and then use a overhead projector to enlarge them to the proper size. Once they are projected onto a sheet of plywood or thick MDF which is vertical up against a wall, I could trace the outline of the drawing onto the plywood then cut it out. These plywood sections are then attached to a strong back and then covered with inch wide by 1/4" thick strips of pine or cedar with a bead and cove milled into the tangent edges like used on a stripper canoe or kayak.

www.actionfish.com

Then I can sand and bondo to my hearts content, then primer, gel coat, mold release wax, and apply PVA mold release agent twice. Is there an easier way to make plugs or is this basically what I need to do? I've also seen plugs CNC machined out of high density foam, but that can be cost prohibitive for larger applications.

With regards to composite pressure hulls made out of fiberglass, kevlar, carbon fiber, etc., when using a high quality epoxy resin or other resin they do have some compressive strength. Look at the Bionic Dolphin which has a carbon fiber outer hull and a kevlar inner hull with syntactic foam sandwiched in between. For the lay up he is using vinylester resin which is not as strong as epoxy resin and he's not going that deep with the craft for a number of reasons not really having to do with the main composite hull collapsing. However Doc is putting an extreme amount of hydrodynamic external stress on the hull when jumping and crashing into the waters surface. Of course the syntactic foam is taking a certain amount of this stress off the outer and inter hull.

http://www.redrockstore.com/resin.htm

http://stinet.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=AD0605963

Regards

Brent

" The difference between genius and madness is a fine line called success."