I have cut down and cut out the outline of an old 42cm slalom fin. Stuck on how to get the profile accurate and symmetrical on both sides. Any tips?
I have seen this on another forum but wondering if this is accurate enough and were to get the print and the measuring



here are a couple pics of the fin, any suggestions, help welcome! Thanks

Hi yew101,

Is the wooden profile the blank or the template? I used to foil wooden fins like that when I was starting out as a kid, plane, spoke shave, cabinet scraper..usually cedar with a glass or carbon centre ply then ply s of carbon/glass and filler resin..lots of elbow grease. The gauges are a necessity however the finish relies on repetition and a naturally good eye and feel..in my opinion..and really the proof is in the performance.

if you are taking that G10 blank down you need some callipers to measure the taper from base to tip as you mill it down in accordance with your specified foil cord thicknesses. Create a centreline on the leading and trailing edge first, to work to. You also use the glass plys as a guide and you measure and count these 'contours' accurately.

Once you have a tapered profile blank you can then start foiling. If you have have not done this before you will need to go very carefully and I would suggest calculating and plotting your cuts on your foil plans first. once you produce a fair cut on one side of the blank, turn it over and replicate on the opposite side so you are always in symmetry. Use your gauge and keep foiling until you arrive at a symmetrical(assuming its a symmetrical foil??)foil, but ensure you reduce te grit of your abrasive as you get close so you can work right to the finish from 80g right through to 400. Your finishing should be 400 to 800..but there are differing schools of thought on this.

Its very hard to explain in a few paragraphs what takes many many fins to learn but all I can say is go for it! One tip..just go with the flow and don't rush.

I love foiling fins!!

Have fun!!

P.S. milling the blank can be done with an upturned belt sander in a vice or better if you have it - 40-60g . I used to use 40-60g on a hard backed 6" sander then 80g on a medium foam pad and then to 120-180 with the soft..very easy to destroy a pad on the fin tip and dangerous at high speed so a rotary orbital can be easier to control. Plenty of hand sanding with good blocks and wet&dry t follow

Take some advice from others as well..there are guys on here making great fins will have some great tricks!

The western red cedar fin above looks like one of mine, I don't remember which at the moment, but is probably a 30deg speed fin I made for yoyo.
I've been shaping fins by hand since the mid 60s, so I've developed an eye for it over the years. So Manoverboard's method is probably better to begin with.

I use a 7" right angle grinder with an 80grit pad under a rubber support. As M.O. says a front and rear center line and a line where the max thickness is also. I start at the front edge taking long even strokes with the grinder, and just remove the stuff I don't want when I get close, I start checking with the profile gauge. As you see on my sheet, I have a series of profiles of different lengths, this does away with having to work out thickness taper. After getting it very close to the desired foil, I then hand smooth with 80grit paper, using a hard pad for the front section and a curved hard foam pad for the rear, this helps get an even concave, but if you don't want a concave stay with the flat timber pad.

When that's nice and even I change to 120 grit, to remove the sanding marks, then spray with an automotive filler, (you'd be surprised how many pin holes there can be in G10, and you don't see them until you paint it.)

OK so your big question is where do you get the profile sheets. well basically I print them out as I want them. Just find a nice foil profile on line, (that's an eppler e836), I then use my photo software to make the series of sizes I need and print it out.

The method seems to work, I've had good results with most of my fins, if I over cook the grinding, there's always bog!

PS, remember fiberglass and carbon fibre aren't real good to breath in so wear a mask!!!!

And the tip about using the cloth layers as a contour gauge is right on, the layers should follow the leading and trailing edges evenly spaced, but the gap between them will get greater at the tip.