Super Reaper Composite Fuel Tank Mold Construction

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Mold Construction - Day 1

I decided to build a mold to make a Kevlar fuel tank for my Super Reaper turbine jet. I first started making a plug so I could create a mold. Here are the rough dimension of my tank.

Here is how the tank will look inside the fuselage.

The next step after the plug was finished to to from a parting board around the plug. I decide to split the tank in half with a right and left seam.

Another shot of the parting board showing the division on the plug.

Another picture of the plug with the parting board.

Because I am using the Sand/Epoxy method of building up my mold thickness, I needed to make sure the parting board would not sag. Since the parting board was constructed using 1/8" sheet balsa I decided to use 1/4" plywood for reinforcement. Notice the plywood is cut short of the balsa edge.

I measured the height of the parting board when it was taped on the plug's center line and cut 3/4" MDF blocks to place underneath the parting board. This will insure that the parting board stays along the plug's centerline during the molding process and also carry the weight of the Sand/Epoxy mix.

Just finishing up the MDF blocks.

The parting board is complete. Next will be the filling of the gap between the parting board and plug.

Before mixing up the gap filler (Epoxy and Cabosil) the plug has to first be waxed with some mold releasing wax. You need to put at least 5 to 7 coats of wax on the plug to sorta season the plug. With the waxing complete I will now apply PVA along the plug's centerline so the gap filler will not stick to the plug. I used some painter's tape to make sure excess mix does not flow onto the plug from underneath the parting board.

I poured out some PVA in a dish and used paper towel strips to apply the PVA onto the plug.

Just make sure to saturate the paper towel with the PVA before applying it to the plug.

The PVA has been applied to the plug and now needs about 2 or 3 hours to cure before I can apply the gap filling mix.

After the PVA dried I then placed the plug into the parting board and prepare to mix epoxy with cabosil to use as a permanent gap filler between the plug and parting board. Most people just use modeling clay, but if the need arises to make another set of mold, you can to apply the clay again. Once the epoxy and cabosil mix dries, it will be sanded down flat against the parting board.

I used a popsicle stick to carefully apply the gap filling mix around the entire plug as you can see in the picture.

Another picture showing where and how the mix was applied.

The mix has now been applied around the plug.

Another picture showing the gap filler applied around the plug.

I let the gap filler dry over night before separating the plug from the parting board. As you can see the gap filler formed a tight fit.

With the plug completely separated from the parting board you see how the gap filler hardened around the parting board edge. This will create a tight permanent fit around the plug for the upcoming molding process.

Another picture. Remember the gap filler will be sanded completely flat against the parting board.

You can see where the PVA is still stuck to the plug. The tape will be removed and the plug will be washed with warm water to remove the PVA.

After sanding the gap filler flat with the parting board, I decide to use tape to cover the parting board and fence walls to create a smooth and slick surface for making the mold. Since I did not have any clear tape in my shop but found a roll of postal tape I decide to use that.

With all 4 sides of the parting board fencing completed I am almost ready to start pouring the tooling resin inside. I used screws to attach the fencing so I could make for easier removal if necessary.

I decided to place the plug inside so you can see how the fencing will contain the tooling resin and epoxy/sand mix I will use to build up the mold thickness.

Another picture of the plug inside the parting board.

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