Hi Andrew
From the looks of your mold you are going to have to grind about 6- 10 mm off the front to get a nice shape. Keep this in mind if you decide to put anything in the fin. I don’t put anything that will absorb water in my fins. If by chance there is an unseen pinhole or something it could swell and split the fin or at the very least add some unwanted weight. The tube with the shot is a good idea but with IOM’s remember that we have a maximun fin/bulb weight. The corrector weight goes in the hull.
I drill a 3/4" hole about an inch or so from the top of the fin and put an aluminum plug in it. The plug has a threaded hole through it from side to side. I drill down from the top of the fin to meet the threaded hole and use a long screw to hole the fin on. Hope you understand that.
Astute is right about putting the uni in first. The uni doesn’t look as nice. I’m just hoping that one day I can pull a fin that doesn’t need paint and filler. Looking for that trick CF look! I have found though, that you can see the weeds on a white fin much better and you don’t have to pull your boat out of the water to check.
How thick is you fin going to be? My layup is for a fin that is about 6mm thick is yours is thicker you could probably get away with less CF. It is really expensive. I think there is about $20 or $30 of CF in my fins. You don’t want to experiment too much at that rate.
Don
I have gotten a few ideas from this thread so far, but have to wonder how you can build an accurate mold by hand. I can see machining two halves that would give you a symmetrical fin, but not by hand from wood.
Why not build a fin then make the mold from it? It would still not be as accurate, but you would KNOW what the finished fin would look like, and could keep sanding and filling until you had what you wanted.
Hew,
I would agree having two halves milled would be the best, but i think this method, not 100% by hand will work just fine. Tne fin thickness at the widest point is 5mm.
Hint/Tip/Suggestion/Crazy Thought …
Get a piece of gutter aluminum, valley roof flashing or similar - twice length of finished keel
Get some 3/4 inch plywood
Cut 1/2 profile of the camber/chord from 3/4 inch plywood
Make enough to allow spacing every 2-3 inches of fin length
Double that number
Cut a back-bone board that is slightly longer than twice the length of the fin
Attach the profile blocks along the length of the back-bone, equal distance
Take the aluminum, copper or whatever flashing/metal and lay along the forms and carefull bend the metal sheet to fit the desired profile.
(You can also do by hand/eye) and eliminate the supporting documents if fin is small enough fron to back.
Spray with PVA or wax for fabric release.
Lay up a layer of whatever composite creation you decide on - with as many layers/plies as desired.
Once cured, lift out the layup, and measure length of fin from one end - and then cut across the layup.
This gives you two pieces (halves) of the fin
End-for-end the pieces and place edges together and it “should” produce a shaped fin that is darn close to your shaped metal.
Glue both halves together and lay up a piece of 1 inch wide tape at leading edge to reinforce.
Seal top and bottom openings and finish fabrication for bulb attach and keel both attach
The general shape will be as good as eyeballing or trying to shape symmetrical out of wood by eye, but using the metal to form the basic shape is easy, fast and while not as good as a CNC milled plug, then having to build a female mold, then layup the composite schedule of materials - provides a definite cost effective keel blade.
Just a thought.
There are reasonably accurate ways to shape wood surfaces by hand. This method works great if you are stubborn and patient. The tail shape shown would make a good fin if made with strong enough materials.
http://www.charlesriverrc.org/articles/construction/markdrela_airfoilshaping.pdf
http://www.charlesriverrc.org/articles/allegrolite2m/tail_shaping.pdf
Oops, one more relevant url:
http://charlesriverrc.org/articles/allegrolite2m/tail_sand.pdf
Sorry to be a wet blanket but I’m with Hew; The pictures show me two pieces of ply with a hollow profile but I can’t see any means of accurately profiling or registering the two halves? When you laminate this the two halves will slide relative to one another and it won’t take much for the result to be a non-symeetrical fin. I think you need some registration pins and these need to be done accurately trough both pieces of ply before cutting the profile.
Assuming the two halves of the ‘mould’ are identical, I suggest laying them up seperately (uni CF| outer layer, then 45deg plain weave, inner layer of peel-ply :zbeer:vacuum bagged ideally), then demould them, remove the peel-ply and glue the two halves together.
You’ll still have a fin with less than optimal aerofoil section but you could improve this by cutting off the LE and gluiing a flat batten along so that you actually mould a fin with a flat leading edge; after assembling the two halves you could then add a LE profile and fair it in?
Ray
Ray,
good points, I had planned on drilling holes along each edge and using wing nuts and bolts to align both pieces. As for the leading edge, after the fin comes out of the mould i would be able to profile it, nothing a good sanding block could not take care of. I am going to vacuum both sides then glue them together afterwards.
Thank you all again for your input.
Andrew
Does anyone know what Claudio uses to build fins? Everything else he make looks real nice.
Andrew - do a search of his AC120 build thread. Not only does he have nice, sharop photos, but lists the composite materials and their order of layup for his fin.
Fin almost done, worked out great. I first Vacuum bagged the carbom skins then glued them together with mico balloons and epoxy. In the middle I wrapped a plastic straw with carbon cut offs, in a spiral pattern with epoxy, when all was wet I clamped both sides together. I just need to give light sanding and paint and trim to fit i fin box. Very stiff fin.