Finished cleaning up the bead and foiling the 25 timber, same method as before, took a couple more pics to make the process a bit clearer.
so I've marked the sheet on the right with a fin profile at 30deg, then put flow lines across it at the same widths as my foil print out, (A to G).
Here the fin is on top of the marked profile, I can then press the gauge on to the fin across the A to G lines and compare to the printout.
Here I'm checking C.
Lots of green arrows coming up so progress may be slow.
Hope the timber doesn't absorb too much moisture and turn into a banana, before I get it sealed.
Looking at the Seabreeze graph for Mandurah....looks great
I hope the X2 did the job on the 43 :-))
Amazing thread, If you don't mind I will link it n to an article on my blog when I finally throw off this writers block! (hoping autumnal winds up here in gb will help that). Thanks for all the detail and pics
As barrel nuts are very hard to obtain, I'll see how well this stuff taps.
I use Acetal rod for barrell nuts.
Get it from the local plastics supply.
It seems to be similar to the stuff they use in Nylock nuts. Never going to lose a bolt.
I use 1/2" (12.7mm) rod.
I drill the fin head holes to size leaving a 4mm section in the centre drilled at at 12.2 and press the rod in then drill and thread for the bolts after its fitted.
The bolts are always tight in the thread.
Great stuff, never stripped any in dozens of fins and it's cheap.
Very informative and great thread. I was thinking about making a weed fin. Now that I know what's involved I'll just go out and buy one! 
Agree with Keef, the easiest way is to rebox an old fin. The thicker and stiffer the better, if you can't find an old stiff one, a layer or 2 of carbon will help enormously.
Thanks guys. I do have a weekend project ready for some on the water testing... Just waiting for my knee to heal before I can give it a test run.
I found an old, fat and ugly Finworks A box weedy. I put one of those Multi fit bases on and if it works I'll get a proper base on it.
Depends how much spare time and spare cash you have, being retired I have much more time than money.
spending several hours and a few dollars makes sense from where I sit.
Sorry but here's a brief diversion.
HOW TO MAKE A HYGROMETER!
Take a piece of dry 6mm thick timber (pine or cedar) laminate one side with a few layers of carbon.
Fix one end to a pedestal so the other end is free to move, attach a simple lever system to the free end, (10:1 should do), short end to timber, behind the long end place a scale, one end humid the other dry.
It'll definitely work, that's the 2nd time I've got fins to a one sided laminate, then had a few stormy days when I abandoned the project for a windsurf.
Both times the nice straight fins have developed a bend, easily fixed though leave them in front of a warm sunny window for several hours. (You just have to wait for some sun!)
Both fins were back to being straight and ready for the next stage after lunch today.
Yoyo is happy with the 9% foil the 25cm has turned into, but I really wanted the 20cm to be 8%, (I think it will have less tendency to spin out at speed downwind, and want to test the theory).
So I've cheated, put another couple of layers of carbon on the trailing edge and bogged it up so it came back to 8%, then when shaping the other side, moved the trailing edge over a bit.
this shows the extra carbon and bog on the trailing edge.
This shows the foil ready for carbon, you can see where I've sanded thru the old trailing edge into the extra layer.
Laminated the carbon, exactly the same as before, they're both under the anvil now.
More bogging tomorrow.
Got the first layer of bog on today.
Used a thick mix of q-cell and epoxy, spread it on the fins with the squeegee then smoothed out with a thin piece of plastic cut from an ice cream container.
That's the yellow rectangle on the box. Holding both ends of the plastic tight against the fin edges, using a smooth dragging action from head to tip, can produce a finish that doesn't need huge amounts of sanding.
Next step is cooking in black plastic to fully cure the epoxy, then more sanding and comparing with the printouts.
Sanded the bog down to the foil printout, then squeegeed on another light layer to fill any low spots.
Just a light sand and they should be ready for boxing.
Well a lot of the previous layer has been sanded of.
The new bog layer doesn't show up well because it's fairly thin, especially over the carbon area.
I made the mistake of allowing for the thickness of 3 carbon layers, then putting 5 on, so I've actually sanded into the carbon a bit here.
Finally got round to molding the bases. (good job yoyo isn't in a hurry)
Because the fin is so small, there's a big area between the trailing edge and the rear of the base. Instead of filling this entirely with resin I'm using a block of high density foam to save a bit more weight. To tie it all together and take the load from the rear bolt, I'm using 3 layers of carbon and a layer of glass on the sides of the base.
First thing is to cover the face of the mold halves in release agent, not just the box part, the whole face, in case resin penetrates the join and glues the 2 halves together.
This is what the vaseline is for.
This time I've remembered to mask out the fin, note that the newspaper is only to keep resiny fingers off the fin, anything more will stick the paper to the fin. The masking tape will stop any excess from the pour off the fin.
Next I wet out the carbon/glass 1 piece at a time and smooth it out in the mold.
Then the mold is bolted together.
Mix up some resin and add some micro fibres, not too much I want a runny mix.
The first time I did this I poured the resin mix in first, then the fin, but this forced the carbon up out of the mold, which blocked the view of the mold edges, making it hard to check fin alignment.
This time I've poured a small amount of resin in first, enough to make sure the timber at the bottom of the fin is covered by resin. The block of foam and fin then go in and are aligned, after that resin is poured in until mold is full, check every 1/4hr or so and top up as necessary.
Today was time for the bolt holes and threads.
From the left, fin out of mold, drill to fit board fin holes, set square vaseline, fin bolt and clearance drill, pencil, dowelling jig with small drill adapter, taps with wrench.
There are several methods of getting a thread in the fin, barrel bolts are probably the most common, but due to a severe shortage of barrel bolts, I'm trying two other methods.
Where there is a solid substrate I'm tapping a hole in the existing material. Where there's only high density foam I'm having a go at molding the thread in.
Whichever method you use, the hole positions need to be accurately marked for the holes in your board.
(I don't trust tuttle standards, there seems to be a lot of variation between manufacturers ).
Here I use a clearance drill for the holes in my board to mark the fin. Don't use an electric drill, just a bit of hand pressure twirling the bit.
once I have a clear mark on the fin base, I use the set square to draw a line across the bottom and down the side of the fin.
The dowelling jig can then be aligned on the pencil line, set the jig to half the thickness of the base.
for the tapping hole I use the small drill adapter in the jig, wrap the drill with some masking tape at a depth that doesn't go all the way thru the fin. As these threads are going to be weak, I want them fairly deep so I can use longer bolts and get a lot of thread engagement. I remove the small drill adapter and use the jig to hold the tap square.
Fortunately the standard hole in my jig is a nice clearance hole for the fin bolt, use a neat fitting drill in the jig and drill the rear hole.
Thoroughly coat a fin bolt in release agent, (vaseline here), work a microfibre mix, (not too thick) into the rear hole. slowly push the bolt into the hole.
Tomorrow will be the test, how well the release agent worked!!!!
I'm not worried, if I can't get the bolts to screw out, I'll heat the bolt with a soldering iron, that softens the resin, trouble is it'll probably ruin the threads as well.
If that happens I'll have to make barrel bolts out of a large stainless steel bolt shaft, unless I can source acetal rod.
An easier way if you're doing lots of fins, is a dedicated drilling jig, fits neatly over the base and has tubes where the 4 holes go. If you have barrel bolts it's just drill 4 holes, a nice press fit for the barrel bolts and you're away.
A bit more tidying up a coat of sanding filler paint and fine wet and dry will finish then off.
JJJJJ Mike, crazy work!! My technic is faster but the fins cost me more and are heavier (also they not carbon!)!! Very master crafty the way you do them, also very well explain, great post ;)))
Thanks Sam,
Well the vaseline did it's job, bolts undid as if they'd been done up fairly tight.
Sanded the front and back of bases for a good fit in the boxes and tidied up a few holes in them today. Tomorrow it's out with the spray paint.
OK both finished!!!!
Here's the first coat of paint.
One of my reasons for painting is to show up any faults. A clear finish over carbon, makes it very hard to see what's going on, a coat of paint instantly shows up any pit holes or rough spots.
I sand this back with 200 to 300 wet and dry.
I quite like this paint, it's high build, so fills imperfections well, it also wet and dries to a slippery feeling surface
After another coat of paint and a 600 wet and dry, my fin is finished, (I let Yoyo wet and dry his own fin)
Threw them in a bucket of water and they float!! Not so worried about weak threads now, much easier to find fins on the surface than on a muddy bottom.
Select to expand quote
, much easier to find fins on the surface than on a muddy bottom.
Hmmm, yep
