Garrie Hill's Female Mold Construction Instructions
Female Mold Construction

3/2010 - By Garrie Hill

OK, so you've labored for hours and hours. Now you have one beautiful tailbox plug. What now? How do you make a mold, to make a tailbox?
Follow along and I'll show you one way of going about it. 
 This step will begin the process of making the parting board. The parting board will create the flange area of the mold
halves. You will need two things for this step:

1) A dead flat surface to work on.
2) A piece of MDF (medium density fiberboard) DO NOT USE PLYWOOD It is not flat.

The plug needs to be rigidly supported in this position for the next stage. A series of sand bags is tucked in to accomplish this.
You might also want to push blobs of plasticene modeling clay in, in addition to the sandbags.

Now you will need a perimeter scribing tool. Using some of the 3/4" MDF, make a notched "L" . Attach a marking pen (Sharpie)
pointing down in the notch of the "L". A wrap of duct tape will do the job.

Now, using the scribing gage, mark all the way around the plug. This will create a transferred profile of the plug ( slightly
larger because the pen is offset to the outside) on the parting board. Do this carefully, as it will save time and aggravation in the following steps.

Using a sabre saw cut out the profile. Use the blade to cut in such a manner as to split the scribe line. After cutting, VERY LIGHTLY
SAND the two internal edges to deburr. 

Build legs for the parting board. Use more of the MDF. The legs' height will be such that when standing on the "dead flat"
surface, the upper surface of the parting board will be level with the equator of the plug (which is also sitting on the "dead flat" surface. Screw and glue
the legs on to the underside of the parting board. 

If you have done everything up to this point, the fairing plug will sit in the parting board with a small gap between it and the parting board. You will now need to sandbag the plug again, in preparation for filling the gap.

With the plug immobilized (sand bagged) and centered in the parting board, it's time to seal the board to the plug. You will need some plasticene modeling clay and a dull putty knife. Roll small balls ( 3/4 of a golf ball) of modeling clay in your hands to warm it up for pliability. Next roll the balls out into "snakes" with a cross section about 1.5 times the width of the gap. Gently press each clay snake into/along the gap. You want to have some of the clay above the plane of the surface of the parting board.

OK, here's where you use the dull putty knife. Hold the blade parallel to the parting board face, lightly place the end of the blade against the surface of the plug, and press down into the clay. When the blade contacts the parting board, draw it back away from the plug while maintaining the downward pressure.

Remember I said a dull putty knife? Here's why: You do not want to gouge or cut the surface of the plug! Still, be gentle with the putty knife; you can still do damage with too much pressure. Follow the "squishing procedure" (Yes, I know. This is a technical term I learned while working on my PhD in Technical Moldology.) all the way around the perimeter of the plug. Done properly, there will be clay in the gap joint, and no where else.

The next two steps are tedious; but necessary. Using a good quality carnuba wax ( Johnson's Traffic Wax Used for gym floors) wipe on a very thin coat.
After this thin coat cures (turns milky white) use a lamb's wool polishing bonnet to buff to a sheen. Repeat three time, varying the waxing pattern each time to guarantee coverage. Next, spray on a coat of a good mold release ( Sprayon S00311 Dry Film with PTFE), let dry and buff. Repeat three more times.

OK, here is another really important step. Use epoxy and 3/4 ounce per square yard bi-directional weave glass cloth. Paint an area with epoxy, and lay in a piece of the glass. Continue over the entire purple area. Tuck in the radius where the flange meets the plug carefully and sharply. You are building what will be the molding surface of one mold half. No wrinkles, bubbles, or gaps. Add two more full layers of 3/4 ounce glass cloth, adding epoxy as needed.

Now, layer on three layers of 2 oz./yd glass in the same way, adding epoxy as needed.
NOTE: Do not "stipple" the cloth down using the end of the brush. This will introduce air bubbles into the epoxy. NOT A GOOD THINGTM

Let the epoxy cure for eight hours. As epoxy cures, it evolves a wax on the exterior surface. After the epoxy has cured, gently, but thoroughly, wipe this wax off with an acetone soaked cloth.

After wiping the wax off the outside of the mold surface (lavendar), it's time to increase the stiffness of the mold without significantly increasing the weight. Cut a series of trapezoidal strips from blue or pink styrofoam. Make the strips about 2" (wide at the base) x 1" (wide across the top) x .5" tall. These strips will be very flexy; which is what we want. Using 3M #77 spray adhesive, glue the strips on to the outside of the half mold to create (as many as you deem necessary) a number of ribs. In this view, the ribs are yellow.

OK!! Almost done (with this side). Lightly spray the outside surface of the mold (and ribs) with 3M #77 spray adhesive. Dry lay one layer of 10 ounce glass cloth over this glue surface, carefully! Tuck it in neatly around the ribs and flange-to mold radius. No wrinkles. Saturate this layer with epoxy (remember, to flow the epoxy on, no stippling with the brush). Now add two more layers of 10 oz glass cloth. As you add cloth layers, push each layer down into the epoxy from the previous layer .... adding epoxy only where needed.

We've added the layers of epoxy/glass in two goes for a reason. As epoxy cures (it doesn't "dry") it gives off a considerable amount of heat. Trying to build up too many layers too quickly, can generate enough heat to warp the plug beyond use. You can generate enough heat to actually start combustion!

After this first half mold has cured (give it two days at 70 degrees F), you are ready to remove the parting board assembly. Gently work the dull putty knife between the mold flange and the parting board surface and work around the perimeter. Equally gently, lift the mold half and plug up and out. Do not attempt to remove the plug from the mold half. It will look something like this.

Clean up the exposed side of the plug. Wax the exposed surface (as before) and the exposed flange surface. Follow the instructions again to create the second halfmold. When done, you will have something that looks like this. Let everything cure for a few more days at 70 degrees F.

Gently work the putty knife between the two flanges and work all the way around the perimeter. Insert some wedges and continue to pry the molds apart. Depending on how well you did the waxing and spraying of mold release, the molds will pop off and free the plug. There is a better than even chance that the plug will be damaged in removal. Excrement happens.

Good luck!

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