I kind of looked around in the resources to fin things about the process of foiling a wooden fin but I don’t have all the angles on how to handle that.
My case : I have got a 5 layer plywood plank, cut out the fin in this case a keel for a twin fish, up to that point everything is OK, now I face the issue with the foil.
I feel like having a 80/20 foil but I don’t know where to start exactly and actually I don’t have any real plan on how to do that properly.
Do I have to draw the outline of the foil on the plank o I know where to go or just pick the power tool and go from one end to the other kind of following a virtual curve set in my vision?
I actually started foiling a keel (double foil, one on each side) but my issue the edges are very fat but rounded with a sharp edge but the thickness of the edge for instance is way to big in order to get rid of the central flat section of the fin.
How am I able to get a rounded foil all the way without having a flat section in the middle.
Right now the edges are rounded but the middle section is all flat so it means that I need to take off some more material from the edges.
I also want to have a foil on each side so I am lost once again, what about of having a foil of a wing (airplane) on one side with for instance a concave on one spot?
I have the vision but I cannot apply it onto the piece of wood.
Do you think it make no sense to foil a fin with a hand planer and a rasp or the power tool is a real must for that kind of action.
One last question : I am just wondering how carpenter without the use of sanding paper were able to have smooth surface after using planer, rasp aso
Check out Larry Allison’s thread on foiling bamboo fins. He draws pencil lines on the fin tempalte to help visualize the foil easily. You can use the same technique with plywood.
First decide where you want the vertical cord (thickest part of the fin) to be. A standard spot is 25 to 30% back off the leading edge. Measure along base cord mark the fin there and perform the same arithmetic procedure up about two thirds of the way up the fin. There’s no sense in going any further up because the tip of the fin will be tapered to thin for this mark to meaningful toward the fin tip.
I start my foiling on the side of the fin with the shallowest camber. I foil the leading edge first leaving plenty of thickness to round off in order to keep a softened leading edge. Once you’ve foiled the trailing edge of the inside of the fin you accomplished setting the center of the trailing edge. Now foil the outside of the fin and taper the leading edge ever more thinly into the tip. Foil the trailing edge starting at the fin base. I believe it is best to start nearly all the foiling work at the fin base. I do the last part of the rough foiling by tapering the tip to suit the flexibility pattern I’m trying to achieve. Rough work can be done with 60 grit. Then move to 100, to 150, to 220, to 400. You’ll be able to put a very nice finish on you work once you get things dressed out. Use a hard block on all convex surfaces except for the working the final contours of the trailing edge if it run concave to the vertical cord of the fin. In this case us something like a half round bastard file go rough nice clean contour into the trailing edge of the fin and finish with a soft block to keep the contour. All concave surfaces on the surface area of the fin should be worked with softly backed grit.
I foil all my fins with a 4 1/2" angle grinder / rasps, then finished with sandpaper. Exactly the same process as foiling the rails on a surfboard but no planer. Draw a center line around the outside edge of the fin all the way around as your reference. I like widest point about 35%+ back of leading edge. Shape, sculpt, cut, be consistent and exact on each side, work at itm all the while sighting down the center line and watching it take shape. Eventually it’s done. More you do the quicker and easier it is. Go for it, no magic, just have a visual plan in mind and begin.
Thaaaank you so much for the very detailled description of the foiling process, now I really have all the angles. I just need the practice but since I have the entire vision of the process it will be so easier. The tip with the lines is great.
The thing that led me away while foiling the first keel were the lines of the plywood layers, by grinding the surface they showed up one after the other but I didn’t have the foil I wanted even if the lines seemed to be at the right place.
The problem with my plywood, the layers don’t have the same thickness so there is not really a way for a beginner to see things clearly right away.
Once again thank you so much for sharing your knowledge and skills.