Regarding the cross-section shape of your handle, the shape you have drawn will not be stronger than a slightly flattened ellipsoid of the same dimensions, but it will probably look cool and give a nice grip
The "perfect shape" for a handle is a "Super-ellipse" (check out the Wiki for the maths of that... It was named and made famous by a danish Poet, Designer and Mathematician)
(My brother who makes custom knives, calls it "the round square" or "squircle" .. best grip in the world...
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If you can work out the geometry of milling/routing out the "inverse shape" of the handle, then that will be a very good way of making a mould directly
I have made high pressure moulds for smaller parts by milling the shape out in stainless steel or aluminium, but it is very time consuming to polish the inside of such moulds to the desired surface quality!!!
I do not make "resin escape" holes in my moulds, it the case of a handle mould like yours, it will be expelled out the ends (only way for it to go ...
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When I had written my post yesterday, and shut down my PC, the idea of the CF braided sleeves hit me as well.. a combination of that and ordinary CF fabric would be excellent, since the direction of the fibres in the braided sleeves would be at close to 45 degrees to the fibres in CF cloth just rolled around the circumference
- I'll explain: Ordinary CF reinforcement fabric has the fibre tows/strands oriented at 90 degrees to each other, if you add a layer of the same cloth, but turned 45 degrees to the first, you will have four strand/tow directions at 45 degrees to each other = very strong in all directions.
Thinking about the use of this tool, I would definitely go for a CF/Kevlar mix as one of the layers in the handle, which is what I do with my axe-handles. (I happen to have a small supply of braided Kevlar sleeve, leftovers from a batch custom made by a rope making company for a University project..
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