Leo has asked how I make my timber carbon fins.
Anybody else interested?
I've just started another 2 so I can document the process here if you like?
As with a lot of things I do, there's a lot of farting about, there's probably a much easier way of achieving something similar.
OK, I'll post pics as the project develops.
Hopefully there won't be anything from me tomorrow, there's wind forecast!!!!!
Got home in time to take some pics of initial progress.
This is the blank for the 24cm fin. I've thicknessed it to 6mm, (final thickness 8mm less 1mm each side allowance for carbon), cut out the profile and marked the centre line with a marking gauge, (that's the marking gauge on the vice).
Next step is to shape the foil on one side.
This is the 21cm fin, it's pine, the 24 is red cedar.
Doesn't show up very well, but the foil is shaped down to the centre line, I've used the right angle grinder in the back ground to remove most of the excess material, then hand sanded to get final shape.
More on how I do that tomorrow.
Got a bit more done today.
Roughed out the 24cm with the grinder.
Note the support under the fin to stop it bending and vibrating.
With the grinder I try to use continuous strokes from the base to the tip, starting at the leading edge in a series of bevels. I treat the trailing edge a bit different, centre the curved surface of the pad about 10mm in from edge, this helps produce the concave at the rear. I've taken it down to within .5mm of the centre gauge mark.
Not everybody will be happy using a grinder, for instance Pepe uses a belt sander with excellent results.
I prefer a flat sanding pad for shaping, but on timber it tends to clog. The pad in the pic seemed very clunky when I first used it, but as it wears out it self cleans, so I put up with it and doesn't feel so bad now.
Next comes hand sanding. I use 80grit paper on 2 pads for this, an ordinary flat piece of wood for most of the work and a firm foam pad for the trailing edge.
By running along the trailing edge, with the curved part of the pad, and the pressure about 10mm back, the concave is maintained.
I use a tyler's profile gauge to compare the timber to a printout of the foil I want.
EDIT. Press the gauge on to the fin, and the shape of the foil is impressed on it, the fin foil can then be compared with the print out. (does that help Keef?)
I have a line at 30deg (the fin rake angle) marked on the bench with horizontal lines across it. This lets me measure across the flow line.
At this stage I don't match the foil, there has to be an allowance for the carbon.
After shaping the foil on one side, the next step is the carbon.
On this fin I'm using 5 layers, 2 full length and 3 successively smaller. There's a mix of 50/50 woven cloth and unidirectional.
A mix isn't necessary, it could be one or the other, but if it's all uni the timber grain needs to be reinforced by running at least 2 layers at cross angles, about 10degrees should do.
Tomorrow I'll get some resin mixed and laminate the carbon on.
Looks like another masterpiece on the way mike a super cool thing 2 do on the forum
Keef, Mike's been making boards for decades. He has the eye of a craftsman. He pretty much gets CNC level accuracy with hand sanding and comparing his profiles by gauge to printouts of the profile he wants. Certainly much better than many fins made from G10 claiming to be CNC but looking like they were hand ground in Asia by someone on minimum wage with not much interest in the finished result.
i just foiled and glassed my first side and its in the bag
mmmmmmm
Laminated today, but first I'll go back to a shaping detail I missed yesterday.
When the fin's in the clamp, and I'm doing the rough work with the grinder, the area at the base in the clamp is untouched. DON'T leave it like this, the foil has to go the full length of the fin!
I didn't bother on an early fin and it de-laminated. By leaving the base thick a concave area is formed between the base and the main blade, when the carbon in this area is under tension, it's being pulled away from the timber.
Bender had a similar experience with his first wide boom mod, between the posts and the flat plate there was a very big concave, this pulled apart under load.
So, here's the start of the laminating process.
It's not meant to be an ad for west systems, I'm sure there are other resin systems just as good, it's just what I used today, I know it's a very good resin and it's available in Mandurah.
The funny looking contraption is my solution to getting an accurate mix with small quantities of 5:1 resin. It's a lever of 10:1 ratio so I can measure tenths of a gram.
In the left bottom corner is some very handy silicone foam sheet, above that is some soft mattress foam.
In the right hand bottom corner is squeegee and Keef's roller, (tried it first time today), and very important, GLOVES, don't play with epoxy without them, epoxy is one of those nasty chemicals that seem quite benign, but slowly creep up on you. After too much exposure you become sensitised, and then all hell breaks loose.
I weighed the carbon at 32grams, typically I use 1.5 times the amount of resin to wet it out, so I weighed 45g of resin and 9g hardener giving me a bit left over to bog one of hardie's fins.
Sorry I don't have any picks of the glassing process, my hands had too much resin on to touch a camera.
But I started by spreading resin over the fin with the squeegee, putting the full length woven carbon over that, then using the roller to smooth it out and draw the resin up into it. spread more resin over that, and repeated process until all 5 layers where on both fins.
Moved them close together trailing edges not quite touching, placed the silicone rubber sheet over them, then the mattress foam, then a flat board and a lot of weight.
This should squash the carbon down, forcing out excess resin and any air bubbles.
The same effect can be achieved with a vacuum bag, but for small jobs like this I find it easier to just plonk on the anvil.
In the foreground is a bottle of vinegar, I use this for cleaning squeegee, roller and gloves. It doesn't act like a thinner, seems to break down the epoxy so it can be removed with a cloth. Doesn't work as well with brushes, it's hard to wipe every bristle!
For that you need a thinner, acetone is no good for epoxy, but the thinner for epoxy paints works great, (not sure how safe it is, smells like you wouldn't want to inhale too much).
If I can get to the fins before the resin goes too hard, I'll cut the excess carbon off with a sharp knife. If not it'll be a hack saw job, we'll see.
Maybe maybe not, but just in case - - -
Speaking of weight, that's main the reason I only shape one side first. If both side were shaped the weight would distort the timber, sitting on a flat side is reasonably safe.
Just had a look in the shed, and the resin was exactly right, gone off enough but not too much.
It needs to be in a firm jelly state, not at all sticky but not quite hard either.
It just takes a minute or so to quickly run around the edge with a sharp knife to trim the excess off.
Be very careful though, the bond strength is far from good at this stage. To see what you're doing, the carbon needs to be underneath. The knife also needs to be used from underneath, so that the pressure is against the carbon into the timber. If the knife is pushing away from the timber it'll probably cause a delam.
Here's how it looked when I removed the weights and foam.
And after trimming.
checked with the gauge, and they're both a tad thick, I'm too used to making 9% foils.
Guess I'll have to loose a bit of carbon.
Yoyo, how do you feel about a 9% base tapering to 8% about half way up?????
Keef reminds me to point out, the blank must be straight and square with no twist before the process is started!
Got skunked today, so came home and got a bit more done.
Roughed out the other side, same way as before, except this time I used some heavy foam on the screw side of the clamp, to protect the fin.
Marked about 5 to 10mm in from the edges with marking gauge.
Then removed the timber inside the marks with a chisel and sandpaper
Next I have to figure out where the screws go and remove the timber there. Then I'll fill with a micro fibre bog. This protects the timber from any water entry and gives a bit of wear tolerance.
Marked the screw positions and removed timber there.
Then filled with a microfibre mix.
30g resin 40ml of fibre made a nice workable mix, but there was almost enough over to do another fin.
Used the mixer/spatula above to work the mix into place and smooth as well as possible.
Can't get a real smooth finish with this stuff the fibres seem to form clumps.
As barrel nuts are very hard to obtain, I'll see how well this stuff taps. Won't be as strong as a brass insert but they're only little fins, and if they come out will probably float.
If that doesn't work I'll have to make my own barrel nuts, not a job I relish, but I've made room for them if needed.
hey mike i wish you put this thread up earlyer , i brought a profile gauge today 250mm and measured my fins
they look a bit sick
There's not a lot a bit of bog can't fix!
The fin I made you has loads, as you'll find when you wear it down a bit.
And that eppler foil isn't the only one that can work well.
