Time to break the winter blues. Who's building what?

Got a double concave ply special underway myself. 134 X 39. 2.5mm ply, 10mm klegecell foam, 2.5mm ply. Pressed together with my garage special 2.8 tonne Laser/Prado press using home made jig.

Anyone got a vac pump set up they want to sell?

Vac bag sounds way easier than finding a means to keep everything lined up while you park the cars on top of the jig.

Also searching for an old LE bladder to patch a couple of large holes in a mates bladder. If you have an old one you thought was only worthing throwing out I may be able to use it.

Cheers, Warren

Yeah Warren ive got a vac pump and vac switch if your keen give me a call

Karl
0427982977

very nice bodiddly except for your footbeds are around the wrong way

how did you shape the rocker and what did you use to seal the ply?

Kaos 69 explains a few tips in building a vacuum pump here I think

www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=20932

Hes even modified it and is using a vacuum advance off an old carburettor to give him regulated pressure.

Nuker, found this sth african kite company that sells fins for
US $2.85 each and post worldwide. The fins they sell had a good write up in another forum.

slipstreamsports.co.za/

cheers

No Probs Captn.

Surfer62 - that was my next step. Find some fins that are better than home made ones from chopping board but still cheap. Might have to give the S.A. ones a go. Thanks!

hey warren,im a boatbuilder by trade um i just use a venturi which you seal to your bag then plug a standard air compressor to it, it creates vacuum somehow. not sure where you get em from though knocked mine off from work. ill ask around and let you know if your still looking for something!!!

nuker i have used the dovetech fins from s africa.they are moulded fbre reinforced nylon and are a cheap alternative to fibreglass or g10 fins.they are a bit brittle and i have have had one snapp but they work great. gary at dovetech will also put a logo on them at a unit price but u usually have to buy a quantity. u can use polyurethane to make a mold of a fin and then use a harder polyurethane to poor the actual fin.again these can be brittle dependingg on urethane hardness and will also need reinforcemnt fibre added to the mix.

I have some dovetech fins if you wanna have a look

see ya

karl

Bunnings has plastic sheet which will work.If you want to borrow a vacuum pump , email me.We tried making boards from plywood laminated around a foam core using a vacuum bag.The first board turned out quite well but snapped after a couple of months so we made three more boards out of thicker ply but they all snapped straight away,which didn't make sense .We want to try again but money is needed for updating gear at the moment.Also have a rocker table,so your welcome to borrow them until we attempt to build another board .If any one is making carbon fiber boards and wants to share there secrets ,I'd love to hear them
Kevin

I want to know If you are a kiteboard builder or a t-shirt designer...Im confused

How many layers of carbon fibre do you need
What are the sizes/thickness of the carbon fibre matting
How much resin do you need
Do you use different thickness on the top compared to the bottom of the board
What the best core material to use
Do you hand shape the core material to give concave or do you form the concave when vacuum bagging
Do you use some sort of plastic for the rails
Whats the best way to form the outside profile of the board and hold everything together when using a vacuum bag
Do you use a vacuum bag or do you use a plastic sheet and suck it down onto the rocker table
What does it roughly cost to make a board

Thanks Kevin

We have made six boards. The first one, we made from 4mm hardwood ply, laminated around a high density foam core. We used a vacuum bag, and induced concave into the bottom by clamping the board over a strip of wood, while the epoxy went off. The board turned out very well, but was quite heavy.

The next board was made from 3.6mm hoop pine ply, in which we sanded one layer of the ply off to make the board nice and light. We knew this would reduce the strength off the board, and were happy when it lasted for two months of high use.

We then bought some 3mm structural hoop pine ply, and made three boards, thinking that we would produce light, strong boards. But they all snapped within five minutes of use, which didn't make sense to us.

We like the idea of using ply, but have been put off after our last experience. Maybe we just got some dud sheets of ply? Graham, how long have your boards lasted, and what sort of ply did you use?

We're thinking of either using lightweight marine ply, or going the carbon-fibre route next time.


Kevin

We used marine ply in the builds .Boards have lasted over a year. Yes I have used carbon before .I like the flex of wood and glass and hopefully getting the right core . I am spending time on graphics getting that right with sublimation for top and bottom of the boards .Dont use carbon anymore ,its exspensive ,no point really.If my boards break it doesnt break the bank.The name of the game is to get the right wood and thickness .I am also trying different woods in the lay up .

Kevin 1.5mm deck, 3mm bottom with core . 200 gsm plain weave on base ,deck and round edge of the two wood laminates .That will stop de lamination .When mixing epoxy for laminating deck and base ,I thicken up with microbaloons .I only carry the core past the foot inserts to give me flex tips .Wood is where its at.

Nuker,

I used 6mm polycarbonate for the fins, they are drilled and tapped to 3/16" (two bolts per fin, spaced about 1 1/2" apart). 3/16" is fairly close to 5mm so the hole has to be pretty well in the centre of the 6mm polycarb.

As for the added strength with multiple concaves, it has more to do with 'distance between the outer fibres'. that is, the distance from the fibres in the top of the board to the fibres in the bottom of the board (imagine laying the board on the ground and measuring from the ground to the top face of the board). The strength of the 'shape' of an object is related to a property known as the 'second moment of area', for an object with a rectanglular cross section, this equals (b x h3)/12. (the breadth, multiplied by the height cubed, divided by 12). Because the height is cubed, any increase in height (ie bending the board into a concave) has an exponential increase in the strength of the shape.
Hope this explaination makes some sense, it is not 100% technicaly accurate (ie the cross section of the board is not a simple rectangle) but might help to get a basic understanding of how changing the shape affects the strength.
A simple way to see this affect is to notice how a ruler bends easily on one axis but is impossible to bend on the other axis. You are trying to bend the same amount of material each time, it is just the distance between the outer fibres that is changing.
Note sure if this trivia is of any help to you but it's as good as you are likely to get from me at this time of night.

Just for the record, I use 12mm marine ply for my boards, tapered on all edges down to about 4mm, sealed with epoxy resin (no glass), single concave. Will post pics once camera is fixed.

I have access to a CNC milling machine which does all the work for me. The hardest thing, is getting machine time, and someone to do the 3d computer modelling of the fins.
Graham do you make your boards in two stages
1-Laminate the ply around a foam core using a vacuum bag
2-Fibreglass the board

Also do you use a vacuum bag when fibreglassing , and would one litre of epoxy be enough to make two boards.Whats the weight of the boards like when finished
Thanks Kevin