one-off mold/plug construction for small-parts

[westsail42]

Greetings all,

Anyone have suggestions/ideas for building a quick-and-dirty plug for small one-off, non-cosmetic parts? That is strong enough for vacuum infusion.

I need to make some "tubs" that will be compartments for things like propane tanks, lazarettes, etc. Compartments that will be mounted on the underside and accessed from the top of a deck of a boat. Since they will be concealed, they dont have to "look nice".

I would like to use sandwich core infusion, so they need to be strong enough to withstand the vacuum.

One idea I got from one of the DIY channels.

1. Use scrap wood to build a frame on a base of plywood and use something like closet rod or moulding for the turn of the corners.
2. Take some stretch nylon fabric (from you local fabric store) and stretch it over the frame affix it to the base.
3. "Paint" the stretched nylon with a thin film of epoxy. This will give it enough rigidness when it sets for the next step.
4. Hand lay up one or two layers of glass over that. Sand and fair that to desired smoothness.

Voila, there is your plug from which the part can be VIP'd.

Sound reasonable? Any ideas or suggestions?

thanks!

[cristofa]

Robert

What size are these 'tubs'?

[westsail42]

Well, the largest might be enough to hold two 25 lb propane cylinders. Say maybe 18"w x 36"l x 30"h. About that size. Some smaller, maybe slightly larger.

[fiberglass jack]

get some 8x4 sheets of arborite the stuff they make kitchen cabnets from , make your box mould, for the corners use fillet wax, and your done. on the out side get some duct tape and seal the joints

[Toot]

First off, parts don't need to be incredibly strong for vacuum infustion. Although there will be considerable pressure on the part, the atmosphere will be the same on the outside and inside of the mold, so lots of strength isn't needed. The reason most molds are very strong has to do with preventing warping as the resin cures.

Just a thought though... If the parts are non structural, and aren't going to be seen much, why even bother with vacuum-infusion?

The way I would handle this is to use MDF (Medium-Density Fibreboard) and aluminum tape. Cut the MDF to the necessary sizes. Cover the wood in strips of aluminum tape (available for cheap at a hardware store, in the plumbing section). Then wax them with a mold release, and screw and glue them into the proper size. Fill any voids with clay. However, if the clay is in a crevice which is open to outside air, it will flow a bit, and for those spots, you may want to seal it up.


To save a few steps, you can even use existing containters. Shoeboxes, wrapped in aluminum tape works well. What about those $10 plastic containers they sell for various storage needs? You can probably wax right over those and pull a part off them.


Fiberglass Jack's suggestion of fillet wax sounds really interesting. I never heard of it until he mentioned it a few days ago. Most of the stuff I build is far from simple dimensions, but I can definitely see some applications for it. Not sure about what it costs though, and am not sure it's really necessary to go through the hassle for a one-time thing.

[Russ]

SOME GOOD IDEAS HERE.
The wax fillets are available in many shapes and sizes as well as sheet wax in many thicknesses. They are used to simulate part thickness when making a male / female matched mold. Bees wax is also used for lost wax patterns (IE) Hollow metal golf clubs. These are materials available from Kindt-Collins, or Freeman supply. They supply stuff to the pattern making trade.
You will enjoy just looking thru their catalogs. Russ

[westsail42]

Toot,

Yeah, I could do a hand layup. But I am trying to favor weight reduction without compromising strenght in this buildout I am doing. I am trying infusion, even on the smaller parts, to get experience in the process. I have all the tools and materials to do either and have been doing infusion experiments on small pieces in the garage. It DOES make a noticeable weight difference!