Ok, so this is how i joined my kite race/ windsurf fins.
first i removed the inserts, then decided on the angle opposed to each other and weather to have them set at anhedral or dihedral.
cut the required angles and check all is good. i then had some carbon rod from inverted umbrella which i cut to make some dowels. i drilled into the tuttle head on both sides, i bonded them into one side when set i cleaned up and filled holes on other fin with resin then bonded and clamped with milled carbonizes resin. check fitment of dowels before using resin. in this one i even used a stainless bolt with a nut on the other end and placed it in where the insert holes were at the back of the wing. just check first where your holes will be!! just for a bit more security but this is optional.
Bond
once set, sand back as necasary and shape the foil profile on the underside. on the lower side in the middle i ground down below my final required shape. this was to take the carbon patch of ud cardon and a bit of kevlar. build up carbon running the ud across the join. build up higher so you can sand back to finished shape. i vacuumed this patch on both sides.
Sand back to required shape, drill holes, i used countersunk brass tube inserts in the holes. this was so the clamping forces was not direct on the carbon/ join etc. i have used the this wing without these but i put them in after. the forward swept wing i put them in straight away.
tidy it up, dash of paint, etc job done.
i made winglets from the tips i cut off of the fins. it worked really well using the dowels and is strong as.
they work really well and are strong. if you like them you can then make a mould from them so if you need to one day, you can replicate it.
Simple as that and pretty quick to do.