As it was not windy today i played around in workshop. I have wanted to start reboxing fins as you cant buy decent quick weed fins.
I knocked this unit up. I have the stuff to make the mould.
The arm that holds the leading edge is on a hinge so i can change the angle as i wish. The ali track that hold the fin is the mast track out a my long gone course racing borad from years ago(Windrush XP). The fins(well all of mine do) wedge in nice and tight so minimal clamping is required.
can anyone see and improvements i could make before i pour in the goo to make the rubberised mould(yes Sam i have ripped off your design).
Cannot see what else you could add Bender..... maybe a computer controlled positioner to maintain the correct angle
What are you going to do to the fin in the picture?
Also do you modify the foil once you have altered the angle? I have a series of different sized images for a particular foil and use that and a profile gauge (pin gauge) plus car body filler to try to achieve what I hear is a good profile. I measure the fin parallel to the bottom of the board and fill/ rub down to try to get the profile. The result is not pretty as I have not taken to painting yet but seems to work.
Evets, the fin in the picture will be used to make the mould for reboxing fins.
It should give me a perfect size and angle for the fin base
The only prob which I can see Bendyman is that your jig is limited solely to 45º, if you want to rebox at other angles or redo a pointer it won't be able to do it.
Also have you a guide for the trailing edge of the fin, you may need that to allign the fin else you make find the board wanting to go in circles
Good point Elmo. I might look at adding a trailing edge guide as well.
I will also make a jig for pointers. This project is mainly to get a good tuttle mould.
hows the name( LEADING EDGE)
I wouldnt bother modifying the foil. When you add rake, all you do is reduce the flow speed component in the lifting direction (perpendicular to the leading edge), and increase the spanwise flow component. Its similar to a plane flying in a sidewind. The spanwise component does not effect lift, but it does create some drag. The reasons you generally need more surface area with a weed fin are
1) you are reducing the effective (lifting) velocity due to the rake by a factor of cos(rake), so the area has to go up to compensate.
2) you are likely increasing the twist (geometric twist where flex becomes twist with rake) so the tip region becomes ineffective at generating lift.
3) The centre of effort moves back meaning it balances differently with the board/body
Old pointers can work great for weed fins. The trick is to find one thats quite stiff to start with, otherwise the geometric twist will kill the performance. They can also be a bit thicker.
Thanks for the info Slowboat.
The fin on which I have increased the foil thickness was quite thin and did not produce sufficient lift to get comfortably up wind. Result was very few speed runs as getting upwind took ages.
It is also all I have in that size (about 22cm) so until I get another I wish to try to make it as good as possible.
So far it has given me my pb of 32.5..... hope it will go faster yet!
As for twist, Decrepit demonstrated what you mean with the fin in question....... nothing I can do about it until I get another fin.
heres a pic of my jig bender,good luck with your project.i've used mine for reheading fins and the two in the pic i've made from scratch.i'm keen to find out what you used [goo] for your moulds,made mine[tiga , power]from polyester resin,there a bit rough but.also keen to find out what is recomended for the fin heads,i used the polyester risin,poked in some matting but concerned they are a bit brittle.
Pirrad, what do you use for release agent?
Have you had any trouble getting the fins out of the mold?
If I remember correct Elmo's first mold was something like yours, he ended up getting his last fin out with an axe!
Bender's using a flexible latex, in the hope that will solve this problem.
I'd like to make a split mold, to make even more certain.
I don't think the base material is all that critical most of the load is compression, polyester resin with cloth in it should be OK, as long as you don't tend to use your fins as hammers!
The Goop which bender is using is the Silicone moulding agent which Sam put us onto
The product is called “Elastosil M4503” and I buy it by 1 Kg for 50 bucks (you make 2 moulds medium size with it)
You can find it at *Fibreglass & Resin Sales* they are in Welshpool
111 Kew St, phone 9470 2571 /
web: www.fibreglass-resin-sales.com.au
The release agent which they recommend is in a little pump pack which actually is supposed to condition the silicone as well as act as a release agent, bender recons it's pretty good.
How I mould my fin bases is in some eyes a bit of overkill.
I always keep as much of the fin as possible so that the fin runs along the bottom of the base, this may loose a little length but I think it makes it stronger.
Generally use 3-4 layers of clothe (don't know whether it's 4 or 6 oz).
I use West Systems epoxy with 206 hardener (the slower one)
I mix in 3 heaped teaspoons of glass fibre pulp, into about 50ml of resin.
I've been using fibreglass split moulds which I made after the "axe removal incedent" but they are starting to look a bit sad, seeing the results of Sam's work I will be starting to make silicone moulds this weekend.
mr. google[fibre glass release agent]told me pva,the only thing i knew of as pva is aqadhere glue,mr. wikipedia then told me of numerous uses for pva[poly vinyl alcohol].i just happened to have a couple of litres of cem stick in the shed and it goes through the spray gun nicely,i spray it on my plastic when i'm vac bagging.
Sorry for got to put down
For the F'glass moulds I use 2 coats of release wax then the PVA release agent
