Does this sound like a good process?


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quinn
q
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I already posted about my carbon fiber helicopter boom, for that I decided I'll bite the bullet and do alloy molds. 
I also need a carbon fiber helicopter canopy. Similar shape to a football but a bit bigger and open at the back, I'll attach a pic of one. It will have pretty thin wall thickness, generally they are about a half mm, maybe .6 or .7. So only a couple layers of weave. 
I will be making my own design on fusion 360 and milling the plug on my cnc. The process that makes the most sense to me is milling each plug half (mold will be split down the middle lengthwise, right and left half) out of mdf or foam, spraying it with layers of duratec primer, sand and polish, then attach each plug half to a flat sheet of melamine or some other rigid plastic to create base for mold flanges and proceed to make fiberglass mold halves from that. I would prefer to skip the plug stage and go straight to milling the molds, but it just doesn't seem to work out as well as making fiberglass molds from a plug.  From the female molds I will vacuum bag a carbon fiber wet lay up. 
does this sound like a good plan or is there an easier/better way considering I have a cnc? Another variation would be attaching the 2 plug halves together to make a complete plug before applying duratec,  then split into 2 molds using the method shown in the air box video, but i feel that it will be less work to just attach the 2 halves to flat sheets for making the molds, just need to make sure both sheets are perfectly flat planes. 

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Steve Broad
Steve Broad
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quinn - 8/8/2018 3:08:45 PM
Lester Populaire - 8/8/2018 2:38:41 PM
quinn - 8/8/2018 2:08:36 PM
Another question, after I'm done with the part and it's removed from the mold, how am I gonna want to finish it? I've heard pva can leave a less that perfect finish. Is a clear coat pretty much inevitable? Also am I gonna be able to sand the seam line from the split mold? I would imagine since I'm not laying any kind of gel coat first or anything like that, the fabric is gonna be right at the surface. Since I'm using infusion, I don't really have the option of building up a layer of epoxy at the joint before lay up right?

I would use a chemical mold release. PVA does a really good job at releasing, but when working with spray tack you often time rip off the PVA film when repositioning the fabric which is no bueno. And as you said the surface finish of your part is only as good as the application of the PVA, so realistically you will have brush marks.
If your molds line up perfectly then you don't need any gel coat or anything. Just sand the Burr with the same grid sandpaper as the mold, or a little finer, and you will hardly see it.

Ok, what would you recommend as a chemical release? Preferably something affordable in very small quantity. The canopy surface is about square 0.2 meter and I'll only do a couple so no need to spend a bunch of money on expensive release that will expire. I imagine maybe I want to season my mold with a few runs using pva? I could just do a few single layer lay ups with fiberglass cloth just to help deactivate the mold surface before doing a canopy with no pva if that would help.

EasyComposites offers Easy-Lease at £6.80 for 100ml

quinn
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Steve Broad - 8/8/2018 8:30:07 PM
quinn - 8/8/2018 3:08:45 PM
Lester Populaire - 8/8/2018 2:38:41 PM
quinn - 8/8/2018 2:08:36 PM
Another question, after I'm done with the part and it's removed from the mold, how am I gonna want to finish it? I've heard pva can leave a less that perfect finish. Is a clear coat pretty much inevitable? Also am I gonna be able to sand the seam line from the split mold? I would imagine since I'm not laying any kind of gel coat first or anything like that, the fabric is gonna be right at the surface. Since I'm using infusion, I don't really have the option of building up a layer of epoxy at the joint before lay up right?

I would use a chemical mold release. PVA does a really good job at releasing, but when working with spray tack you often time rip off the PVA film when repositioning the fabric which is no bueno. And as you said the surface finish of your part is only as good as the application of the PVA, so realistically you will have brush marks.
If your molds line up perfectly then you don't need any gel coat or anything. Just sand the Burr with the same grid sandpaper as the mold, or a little finer, and you will hardly see it.

Ok, what would you recommend as a chemical release? Preferably something affordable in very small quantity. The canopy surface is about square 0.2 meter and I'll only do a couple so no need to spend a bunch of money on expensive release that will expire. I imagine maybe I want to season my mold with a few runs using pva? I could just do a few single layer lay ups with fiberglass cloth just to help deactivate the mold surface before doing a canopy with no pva if that would help.

EasyComposites offers Easy-Lease at £6.80 for 100ml

I didn't look at the shipping, but I assume it's similar to when I tried to buy s120 sealer. Like 60 bucks shipping for a 10 dollar item. Really sucks that I can't use the products from easy composites. Wish I could, but shipping chemicals from UK to US is just too expensive. Do you know of another product this would be similar to? Maybe similar to frekote? I looked into that a bit. Some guys swear by it, other prefer wax and pva

GO

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                     EasyComposites offers Easy-Lease at £6.80 for 100ml
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