pilott34

Hi guys,

Ive been doing some experimenting with making molds. I havent been too successful up until now, my first try was an F-15 drop tank. I ended up breaking the mold and I gave up...

Some time has gone by now and my curiosity levels are back up. So I figured I would try something easy like a square fuel tank. I went to home depot and bought some pink foam sheeting. I cut squares out and glued them all together. Then I sanded it down as close as I could get to a rectangle. I then rounded all the edges. I then used 1oz f/g cloth and some finishing resin and glassed the whole thing. I sanded it down, and it still had some high/low spots. I then coated it with some 6 min epoxy, and its drying as I type this thread. Here are a couple pics of what I have so far...

Mike

pilott34

I have built a box out of wood as a dam. I went and bought some plaster to make the mold out of. My plan is once the plaster is dry, to seal it with some west system or finishing resin. I also bought some PVA to coat the mold once complete.

Does all of this sound like the right process?? Am I missing anything?

Mike

esamart

Plaster mold is very stiff therefore part removal is harder. Consider if the parting line should be diaconally.

If you use wet seam the mold must have a access hole. Usual fuel plunger fitting size might be too small and the plaster mold thickness is rather thick which makes working with the seam work difficult.

bruce88123

Take a look at this "tutorial". Looks like a plan to me.
http://www.houstonhobbies.com/tips/c...r-fueltank.htm

dreadnaut

My Feedback: (5)

I think you are missing the ''draft angle''. If you try to mold a part with sides that are perpendicular to your parting line, it will be impossible to remove it from the mold, or the mold from the plug, without breaking it. For a piece that big I would use 5 degrees.

Newc

Out of curiosity, why are you doing this?

pilott34

Just trying to learn how to mold. No other reason. Ive just heard other people molding things and it caught my interest.

I see what you are saying about the draft angle. That makes sense. The plug I have is 6"X8" so its not really big. Ill see if I can put those angles on it though. I made the parting line out of tape so one side will fit into the other. I have some west system I was going to use on the glass.

Mike

Newc

Seems like a great reason to me.

From your addresses, are you in the service?

pilott34

yes...navy instructor pilot

charlieoneseven

Nice start with the plug pilott34, other than plaster I have used polyester resin with chop strand mat and bondo to make small molds. painting the surface of your plaster mold will help prep it for making parts. check out www.fiberglast.com they sell the duratec primer that is highly recommended for surfacing parts and molds and have some tutorials on the learning center page. Depending on what material you plan to make your parts is how to select mold materials. Epoxy parts need epoxy molds, polyester parts in polyester molds. Mixing the 2 materials isn't recommended. I prefer epoxy now using west systems due to it's variety of hardeners and sources available. Waxing and buffing the molds and plugs 10 times sometimes seems excessive but good practice before you spray the PVA that is the best method. Make 2 or 3 light coats with that instead of one heavy pass to preserve the details, I really like PVA it is self leveling and makes a smooth surface to cast parts against. Making the 2 halves of the mold key together is a good practice. I added graphite powder to the first coat of resin showing that goes against the plug to give the mold a durable surface and it makes wetting out cloth much easier when you have a black background. If you use epoxy be sure to use the right ratio of hardener or it will never harden right. Here is one I just finished I made the second half key into the first half flange by making 1/4" wide drill starts around the flange before spraying PVA on the plug and first half of the mold. I used clay against the part to seal it to the parting plane along with some tape to hold it in place without attacking the plug. You can also used a little bondo in the gap if you have waxed the whole plug before attaching the parting plane. I remember seeing someone making a tank like yours they made a 3 part mold leaving the seam exposed with the 3rd part out to apply seam tape. There is a big market for kevlar tanks right now and they are using screw in stoppers and various fittings glassed right in the tank. Joining them in the mold with thickened epoxy is common so don't get in to big a hurry to take them out if you plan to try that. Trimming the excess cloth hanging out of the mold while the resin is still soft is also prefered to waiting until the next day when you just about have to take it to the sanding wheel to trim it.

dreadnaut

My Feedback: (5)

I use Partall and wax it real good. It was recommended to me to use a heat gun to melt the wax before buffing it off. I have tried it and it does seem to reduce the number of coats needed. I usually use three now.

This is recommended, also because it reduces the friction coefficient of the mold surface. Slippery molds release better.


Charlie. - I haven't forgotten about the foam. I will be able to get to it after the first of the year.