lamination frustration

[BelowPAR 0]

I have just started building my own kiteboards, the process im using is similar to skateboard construction, involving a number of vertical laminates that are glued and moulded in a vacuum press (the type where you cross your fingers that you got all the air out to achieve the 14psi, and the pegs holding it shut dont fail at 3 am - not the type that squeezes 300psi).

 

So to start with i have built a few long deck skateboards just to get the hang of the construction, and how it all works out once the resin dries.

 

So far the problem is in the stiffness of the board.

Initially i didnt expect it to be a problem and the first board was;

4 laminates of 1.5mm 3 ply gaboon with top and bottom triaxial stringers (approx quarter width of the board and run lengthwise down the centre of the board, with finishing veneers making the rest of the width) AND a full layer of triaxial on the bottom of the board.

 

Second board had an extra laminate of the ply and was no stiffer, third board swapped the e glass for carbon fibre, fourth board was to be a mahogany core (3ply 2mm), but instead i made up 10 scaled down samples trying things like hardners in the resin/carbon core/e glass making up some of the laminates compared to on the bottom etc.

 

Just waiting on them to dry and was scouring the net for some theory, but i cant seem to find much. Then i realised half the people on here do it for a living, (and the other half for a hobby ).

Anyone got any advice? How do i stiffen it ? Whats some of the basic theory behind it? relationships between adding a laminate and increasing stiffness etc, my main concern is why can i not see any difference in the different materials?

 

Im thinking it could be the timber, as i pretty much went on the advice of the bloke after i told him the properties i wanted. Any thoughts?

 

Cheers Ben

 

btw despite what isaf say, kiting is sailng - so this is marine talk

[Guest]

the key to stiffness is creating a sandwich. you will need to put near on the same laminate on the top of the board as well.

then for extra stiffness you could add more laminate or make the board thicker. try and stick to the recomended resin mixing ratios. you will only end up with a rubbery brew or a little more brittle that will bleed the extra hardner.

most composite engineers don't count the resin properties between different types untill you get to the very high end of things

[Tubthumper 0]

Agreed,

 

Put the stiffer material (e glass, carbon, boron(why not!)) on the outsides and the least stiff (foam, honey comb) at the middle.

 

If you're going for lowest weight, use a thicker core for less laminate, although there is a balance.

 

Maybe figure out what deflection you're happy with when it's got max weight on it, then you can engineer a beam to suit.

 

As far as resins go, make sure you use the right mix and make sure it all cures once and once only, you don't want it warping later.

[Kiteroa 8]

From my experience a laminate could be:

 

CWR 0/90 200g

CUD 0 400g

CDB +-45 400g

12mm H80 foam core

CDB +-45 400g

CUD 0 400g

CWR 0/90 200g

 

That's the laminate from the last one I helped out with was anyway. Some local reinforcing around threaded inserts and fins might be a good idea. West system epoxy (5:1 mix ratio) is good enough for this application although don't paint it a dark colour and leave it in the sun.

[BelowPAR 0]

cheers guys

when i said adding hardners to the resin, i just meant standard glue powder type hardners - not touching the mixing ratio which is to forever remain 5:1 (unless the pumps send out something different )

 

So a sandwich, with the stiffest stuff on the outside, that pretty much sums up my little experiment (tho minus a bit of coins worth of fibres and resin). The only thing that went against this was using a mahogany ply core, and the more flexible gaboon outer.

 

CWR 0/90 200g

CUD 0 400g

CDB +-45 400g

12mm H80 foam core

CDB +-45 400g

CUD 0 400g

CWR 0/90 200g

 

uhuh nothing like being specific will be in touch.

[Panic 0]

Is your board more bendy to start with and stiffer,once a bit of bend has been induced?

 

If so you could try building in a bit of prebend in the core. A bit like a bit of prestressed concrete beam. You can achieve a lot more stiffness through the shape of the structure than by adding a load of glass, the down side is once it reaches its maximum load it will go bang real quick where as a board which is more glass than core may well bend alot more before it ultimatley gives up.

[BelowPAR 0]

thanks panic - the boards are prebent - tho in the opposite to which force is applied. ie lengthwise, the middle of the boards are raised. I dont know why this is done, but any board ive ever ridden has the same concept so i just copied it.

I this what you meant?