kramer714
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I'm starting on a new rocket for m-n hybrids. I have never liked the 'fill in the corners' centering ring bulkheads I have used on other projects. Plus I like the idea of being able to use screws to attach bulkheads. The rocket i'm building is all fiberglass 7.5 inch diameter 144 inch long.
To make the bulkheads I machined a mold out of aluminum. It looks like a dog bowl, 7.5 inch inside diameter, 2 inches deep. I also cut a 2 inch hole in the bottom. There is a slight taper .005 inch from the bottom to top to help removing the part.
To make a bulkhead, first i plug the 2" hole with a test plug, these are the expanding rubber plugs used to check plumbing. It fill the hole and is recessed from the bottom. I wax the tool with Partall release wax. If done correctly you wax the tool, let the wax harden and buff it out (I have made 6 of these bulkheads, none stuck).
The materials I use are :
7.3 inch diameter plywood disk 1/4 inch thick for centering rings, 1/2 inch thick for shock cord mounts.
2-2 twill weave fiberglass cloth around 9 oz, 6 squares cut 12X12 inch, clip the corners to make octagons from them.
Epoxy (I use commercial stuff, but West system would work fine)
Step 1) Mix the epoxy, I mix 150 grams for a bulkhead and have plenty left over.
Step 2) Take some of the epoxy and mix in milled cotton fiber to make a 'toothpaste' consistancy paste. Coat the entire tool with it. This gives a nice smooth finish.
Step 3) One at a time, place three layers of fiberglass in the mold using a stiff paintbrush press the dry glass on the wet tool until the fiberglass is saturated. work the edges up the sides without cutting, this can be done seamlessly using the twill weave. paint on a little more resin and repeat until there are three layers in the tool.
Step 4) paint epoxy on the wood disk, if I have any left over 'toothpaste' i use it up here. Carefully press the wood down onto the bottom of the bowl, wiggle it a bit until resin comes up from below.
Step 5) One at a time, place the three remaining layers of fiberglass in the mold using a stiff paintbrush press the dry glass on the wet tool until the fiberglass is saturated. work the edges up the sides without cutting, this can be done seamlessly using the twill weave. paint on a little more resin and repeat until there are three layers in the tool.
Step 6) Trim the top of the mold, leave some fiberglass sticking up but cut down the excess, press the inside corner down well, I use a top of a jar for this it gets into the corner better than a squegee.
Step 7) To demold, remove the expansion plug and, I use a 2" wood dowel and tap the part out, It does help to work the edge a bit with a screwdriver or thin shim. It usually takes one good hit and then the part taps out cleanly.
Step 8) Trim the top (I use a lathe) and cut in a hole if you are using it for a centering ring.
I don't have any pictures during the glass work (sticky hands don't mix with digital cameras), if there is enough interest I can have my kid take pictures next time I make one.
Mike
View attachment AUT_1566.JPG
View attachment AUT_1564.JPG
View attachment AUT_1563.JPG
View attachment AUT_1560.JPG
View attachment AUT_1562.JPG
To make the bulkheads I machined a mold out of aluminum. It looks like a dog bowl, 7.5 inch inside diameter, 2 inches deep. I also cut a 2 inch hole in the bottom. There is a slight taper .005 inch from the bottom to top to help removing the part.
To make a bulkhead, first i plug the 2" hole with a test plug, these are the expanding rubber plugs used to check plumbing. It fill the hole and is recessed from the bottom. I wax the tool with Partall release wax. If done correctly you wax the tool, let the wax harden and buff it out (I have made 6 of these bulkheads, none stuck).
The materials I use are :
7.3 inch diameter plywood disk 1/4 inch thick for centering rings, 1/2 inch thick for shock cord mounts.
2-2 twill weave fiberglass cloth around 9 oz, 6 squares cut 12X12 inch, clip the corners to make octagons from them.
Epoxy (I use commercial stuff, but West system would work fine)
Step 1) Mix the epoxy, I mix 150 grams for a bulkhead and have plenty left over.
Step 2) Take some of the epoxy and mix in milled cotton fiber to make a 'toothpaste' consistancy paste. Coat the entire tool with it. This gives a nice smooth finish.
Step 3) One at a time, place three layers of fiberglass in the mold using a stiff paintbrush press the dry glass on the wet tool until the fiberglass is saturated. work the edges up the sides without cutting, this can be done seamlessly using the twill weave. paint on a little more resin and repeat until there are three layers in the tool.
Step 4) paint epoxy on the wood disk, if I have any left over 'toothpaste' i use it up here. Carefully press the wood down onto the bottom of the bowl, wiggle it a bit until resin comes up from below.
Step 5) One at a time, place the three remaining layers of fiberglass in the mold using a stiff paintbrush press the dry glass on the wet tool until the fiberglass is saturated. work the edges up the sides without cutting, this can be done seamlessly using the twill weave. paint on a little more resin and repeat until there are three layers in the tool.
Step 6) Trim the top of the mold, leave some fiberglass sticking up but cut down the excess, press the inside corner down well, I use a top of a jar for this it gets into the corner better than a squegee.
Step 7) To demold, remove the expansion plug and, I use a 2" wood dowel and tap the part out, It does help to work the edge a bit with a screwdriver or thin shim. It usually takes one good hit and then the part taps out cleanly.
Step 8) Trim the top (I use a lathe) and cut in a hole if you are using it for a centering ring.
I don't have any pictures during the glass work (sticky hands don't mix with digital cameras), if there is enough interest I can have my kid take pictures next time I make one.
Mike
View attachment AUT_1566.JPG
View attachment AUT_1564.JPG
View attachment AUT_1563.JPG
View attachment AUT_1560.JPG
View attachment AUT_1562.JPG
