That process you descibe sounds like it will be faster as well.
I’ll give that a try, thanks!
1)Putting a gel coat into the mold first might help the bubble at the edges? The resin could flow in to fill the voids?
2)I have a huge tub of milled fibreglass, it’s useful for making the mold surfaces strong and chip-resistant.
I’ll add some to the gel coat of the fins, so the outer layer of resin will be strong and hard. Then it will be ok to build up the sharp edges a little with resin only.
The resin that forms the sharp corners of the FCS tabs will be much stronger with the milled fibre also. I assume that the carbon cloth can’t fold into the sharp corners of the tabs?
Kit
hmmm…
I think u made a salad from what I wrote…
1) as i understand , u want to use gelcoat as a part of the product…why is that?
about resin filling the voids...well...I think it will make the part heavier, fregile and not homogene.
won’t it?
2) I didn’t really get you on this one…
do u paln adding chopped-fibers (milled) to the mold it self ( during the mold making) or to the fin u are making in it?
its better using chopped carbon fibers rather than fiberglass.
anyway fabric is allways stronger then milled/chopped fibers.
I use to fill the tight corners ( fin tabs) with small amount of chopped carbon and then fabrics. it's beter than filling the whole tab with
chopped fiber slurry.
u wrote u assume that the carbon cloth can't fold into those tight-cornered tabs. u'd be amazed what that cloth
is capabale of , especially if u apply both chopped fibers and cloth in that case.
GOOD LUCK
wait to see your work, I can always learn new things and tricks....
Yeah, I did write that post in a pretty disorganised way
Quote:
do u paln adding chopped-fibers (milled) to the mold it self ( during the mold making) or to the fin u are making in it? </blockquote></div>
Both! It makes the mold stronger as you know, and also any resin on the fins that does not have cloth in it, maybe some of the funny little corners that the cloth can’t get into.
The FCS tabs would have plenty of carbon cloth in them, but I was expecting to have to add resin to fully fill all the square corners perfectly, so I thought adding milled fibres would help to stop them chipping/cracking easily. It sounds like you do it a similar way, using chopped carbon fibres.
I’m hoping that if I use as strong vacuum as I can that there will be no air bubbles, and the cloth will fit into every corner!
do you need multiple entry points for a fin or is one hole enough?
Depends on the setup and the resin. I experimented on a glass table so I could see what was going on. Injection from one point should work fine but you have to watch for resin creeping around the edges faster than it move through the body of the laminate. You can get islands of unwetout fabric. It’s not difficult to repair if using a vacuum bag. Get a big syringe needle and connect it to the vacuum line. Stick some sealant tape over the middle of the dry area and stick the needle through the tacky tape and into the bag. Assuming the resin is still flowing you have now introduced a new vac point and the resin will flow towards the needle. When it arrives withdraw the needle through the tacky tape and seal the hole as you remove the needle. Works a treat.
Obviouysly next time the feed line needs repositioning.
Personally I use 2 techniques most often depending on what one is making.
suck all around the edges and inject at the centre
suck from the middle and inject all around the perimeter.
This covers most situations in my trade.
can you do three fins at once?
No worries, I have students doing 6 or mare test panels at the same time. BUT if you have a leak in one setup you lose pressure in all the others. I’ve not used inline one way valves but that might sort the problem. Also I am fortunate to have a back-up pump in case the first pump goes down during a big infusion (boat). I must say that it has never happened but could get really expensive on bigger stuff.
There is a product on the market called “Rovicore”. It has chopped glass on each side and a fibrous material in between (polyester I think). It is designed to act as a resin transfer medium. So you could layup carbon / rovicore / carbon and not need such cunning injection points. It acts as a core and bulking material. Maybe it holds too much resin and makes things too heavy. But If you are using carbon skins you are saving on weight and getting a stiffer product so whatever is in the core only needs shear strength, and this stuff is pretty good. I could send you a bit if you’d like to experiment.
Hey Lee Jordon, Now see what you’ve done. Got us all thinking about great new ways of doing things, and on the cheap by working on small, handy, table top, inexpensive fins. Way to go! and thank you again.
Variants of composite constuction go on add infinitum.
I’m in Greenough’s camp: weave or grain should be on the bias and the layers of construction should foil the curvature of the fin as much as is possible. With this approach the fin will function with a more lifelike movement than any other way. Foam core has it’s place but consider that putting a sheer panel on either side of a central foam core yeilds a very stiff yet very fragile result. Making fins to suit a board, conditions and a specific surfer is no small task.
Carbon has it’s place: It is IMHO to create stiffness and to increase more immediate recoil. The stuff is very tuff too.
Just a random thought, but if you want a cheap pressure injection system, you could use a “grease gun” like is used to inject grease into grease nipples on mechanical parts.
Sounds kinky eh?
Just fill the thing with resin instead, probably wouldn’t be too hard to clean.
have an injection line with a normal grease nipple attachment.
Pretty low budget from Super Cheap Auto or Repco.
No idea if it would be appropriate, but thats what popped into my head!
Looks interesting. The thing about moulds is that they must not distort under either internal or external pressure. How stiff is that rubber?
I have had success (especially with small split moulds, rudders / centreboards) by building a channel into the edge flange to take a silocon rubber “O” ring gasket. Place this flat on a (thick) plate glass table (those flashy coffee tables work a treat!) apply vacuum to a port in the mould and it will suck itself tight against the glass. No clamps and no distortion if the mould is stiff. Remember that as soon as you open the vacuum flow line the pressuse in the mould will drop a little. To lessen this we evacuate the mould (with all the laminate tacked in place) and leave it to suck for 20 minutes, then allow the resin to flow until it just enters the mould. Clamp it off again and that little bit of air that was in the feed line can now be sucked out for 5 minutes, then open the feed line and away it goes.
No bubbles or voids.
Obviously this way you should end up with a glassy smoothe surface against the glass.
The same can be done with a split double mould, so that central fin with foil shape on both surfaces can be done in one shot.
Halcyon is, of course, dead right. The variety of flex etc. is endless depending on materials, weave pattern, fibre alignment and cores.
Oh for more time and no students so I could fiddle the years away in the workshop, I’d probably never get in the water!! Actually that’s not fair on the students, they are great enthusiasts, trouble is we have to follow a curriculum that was not developed by surfers! I am working on a real surf based syllabus…
I don’t know much about infusion but I’m pretty sure at least one fin company is using this stuff to get better, faster flow through the laminate. It has the appearance of honeycomb foam but is actually microspheres embedded in a fabric matrix.
Yep, that’s Lantor Soric. It comes in various thicknesses and is designed to go on the centreline of the laminate stack. I did some tests for a boat panel. One panel was a normal dinghy layup with distribution mesh and the other was reduced in the skin thickness and the Soric on the centre plane with no mesh. Bit disappointing how slow the Soric was. For smaller items it would not be a problem and it can look very cool. It does adsorb extra resin and the laminate comes out quite heavy but well worth playing with.
I can post pix if anyone wants, they’re at work so it won’t be before tomorrow…
