Fin Box Mold?

General Discussion
1

If I wanted to make a mold of an old fin box (specifically with epoxy), is there a way that I could pour the resin right into the box (pictured), set a fin in it, and be relatively sure it would all pop out okay?

I see that Fiberglass suppliers sell mold release products – I also thought about lining it with wax itself.

Best,

HerbB

2

Herb, are you saying you want to make a mold of the box, or use it as a mold and cast a fin + tab right in the box?

3

Yes, I would like to use the fin box (that is pictured) as mold, and cast a new fin in it.

I was using the wrong terminology - thanks for helping to clarify.

Herb

4

Think you could do it with some thin sandwich wrap type plastic.

5

Thin plastic is a good idea if it will stand up to epoxy without melting. Is that a Hobie? Check this site and take a look at the slot at the front of fin base. Might have to fill and cut the slot after removal. Do you still have the through the deck screw? A threaded insert will need to be inserted in the fin base as well.

http://www.oneworldsurf.com/reprofins.htm

6

Just use mold release or beeswax to coat the positive and pour whatever your mold material will be in/on it(you can temporarly box it in w/ masking tape.This will act as a dam)…this will make your negitive(mold).

With a finbox; it have to be at a two piece mold, unless you use silicone flexable mold material.Herb

7

I do have deck screw, and the original fin. This original fin has a lot of surface area and I just trying for a more modern, looser fin template on the board.

With having the original fin, do you think I’m going in the right direction by using the board’s original box to cast a new fin in? Or should I be thinking about making a mold of the orginal fin’s base from silicone or clay, and using that to cast the new fin in.

Thanks,

HerbB

8

i would say if you want to mold the shape of the fin base you will need at least 2 sides of molding surface to get your base out of the mold…3 sides might be even better…i work in plastic injection molding and what we call mold release ,that you mentioned, i would not want to use with anything surfboard related…it is for plastic in my case…and has little to no effect on wether the parts release or not…but of course you will have to get the resin to release from your mold…so i would mess around with diffrent stuff…grease , wax, who knows,just mess with it maybe find the right stuff then use it on the real thing.

9

I had that same urge when I had an old Corky Carroll Mini-Model, but I never tried it. You would need to plug up the front of the box with wax or silicone caulk so the epoxy resin wouldn’t get more than half way past the dowel pin.

I do think it might be better to make a mold of the base of the orginal fin. I helped make a rubber latex mold of a pillar years ago. It was supported by an outer mold of plaster and burlap. I did a little googling for “latex rubber mold” and turned up this info about silicone molds. Looks faster than latex.

http://members.aol.com/fostrak/silsum.htm

Another place to look for info is from the same supplier that sells epoxy resin in your town…a big supplier. They may carry molding materials, and you can pick their brains a bit.

A wood fin sealed with a thinned out epoxy might be worth considering.

10

I made a mold from a microwavable plastic chinese takeaway food container. Just cut down each long side approx 3/4" in and joined the two sides together with masking tape. Fill with rovings, put the fin in and filled with epoxy. The top of the mold has a lip all the way around so you can rest it on the teeth of a vise.

When it’s set, remove the masking tape and the two sides just peel off. Shape to size looking at a fin that fits the box.

Worked for me.

Hicksy

11

thanks for that hicksy…that’s a good one to remember, as I have the fin off the cordingley I’d like to be able to mould a base onto ! I’ll give that a try with one of my FCS I’ve made first… maybe one of the aeroplane tail fins…the clear one.

    "chip"
12

http://www.mouldmaking.freeserve.co.uk/

13

Can’t do it, why? the fin that goes to that box is molded with a relief to it. The front pin will prevent you from getting it out of the box, the fin moves downward as it goes into the box, thusly the front opening is wider to accomodate this action and the underside of the base is rolled also, all things that let the fin go in and out. Now if you had the fin, you could mold from it

14

Ive pulled some fairly complex male plugs using commercial grade polyurethane. First, I flushed the female portion w/silcone based wash (Ive even used thin car wash/wax), thoroughly drained/dried and then poured in 2-part (catalyzed) polyurethane. The cured male plug will usually flex and stretch enough to be removed in one piece. Use a softer durometer, under 50A. After that, an accurate female mold can cast around the polyurethane male plug. I recommend doing a couple similar (inexpensive/disposable) experiments first…

15

You’re right - Jeeze that was a blatant observation (hard for the rest to see in my pic) that I shouldn’t have missed. I won’t be able to use the box because of the pin - Thanks for pointing that out.

My only option will be to make a mold from the original fin’s base (which I have). From some of the links provided (thank you) - it looks like silicone is the preferred product used to make a mold. Does anyone have any experience using plain old household silicone chalk/tubes for this? Seems like it might be a little thick for my application though?

HerbB

16

You could still use the existing box as a mold…

As Poobah suggests, cover the horizontal pin area with a gob wax so the cured epoxy will lift out(plug the screw hole with wax or tape also).

As Dale suggests, coat the inside with wax or mold release.

Lay up a panel of approx. 10 layers of cloth, cut your template, center it and hold vertical with tape across the top. Mix some epoxy and fiber and with box surface level, pour in box. After it cures, pop it out, add enough epoxy/fiber material to front of base to accomodate the pin slot - I’d cut few slots, rough it up good and use carbon strands for reinforcement. Use tape to make a little mold at the end. Cut your slot as on original fin.

  • Cost of tape to make the little mold = Less than a penny.
  • Cost of urethane or silicone to make a mold of fin base = Could be quite a bit.
Add foam or wood to sides of fin panel, foil, add more cloth, hotcoat, sand, gloss. Install threaded insert for through the deck screw and you should be set. You will have saved the time and cost of making a new mold which you basically already have. The fin might even fit better since you're casting directly from the box.

If you hit something and that little pin slot addition breaks off, consider it a safety device that prevented damage to that nice old board.

Oh yeah - dig out the wax plug with a knife or screwdriver.

Here’s another link to a site that lists many suppliers of mold making supplies. http://www.lumicast.com/links.html