Nice and neat Mike, my freehand routing left a few gaps, I've been working more bog into them today.
Select to expand quoteStuthepirate said..
Mike, if inclined could one glue the 2 x left blocks and 2 x right blocks as one whole block each? Ie 2 tetris shaped blocks. 1 for left fins and and 1 for right fins?
Like this www.seabreeze.com.au/forums/Windsurfing/Wave-sailing/Started-shaping-my-new-waveboard
As Mark says for me less wastage. I got my pvc guy of a makes canoes, I had to beg and .....oh lets not go there. Anyway it was the only way tocut it from the bit I got, ideally id like a thicker block, also this board has 3mm deep double concaves in this area so 2 seperate bits helps make a verg shallow vee to be shaped into the concave.
Select to expand quotedecrepit said..
Nice and neat Mike, my freehand routing left a few gaps, I've been working more bog into them today.
Thanks mike. As you know tge tighter the fit tge less bog and less added weight, I used 60ml ogtr resin for 4 boxes and glueing more on to make thicker blocks.
Select to expand quoteMark _australia said..
You blokes jinxed me.
Broke my router today.................... 
You can pop over and borrow mine.
How thick is your pvc?
^^^ from memory 14mm and 16mm segmented..... so two layers does a mas track nicely.
Then a big sheet of 25mm being saved for best :)
This is the sandwich layer most other boards I've seen use a pvc material this one is extruded styrofoam I poured some thinners on it to see if it disolved.
This is the outside skin thin probably 2 or mmaybe 4oz glass, wood, more 2 or 4 Oz glass, then paint. It's going to be tricky feathering such a thin layer of glass for my layer of glass to stick to. Very easy to sand through to the wood.
Dodgy pricks using XPS over EPS, would be nowhere near as strong. 
Has it been previously repaired? I'd hope so as JP / Cobra would surely not do that?
(wouldn't bet my last dollar though, that's for sure....)
well it has got wood over it and it looks thick, more than 5mm???? So it should be fairly stiff, and the wood will give it impact resistance. Does seem a tad dodgy though
So the HD foam blocks are stuck in with Q Cell and Resin and weighted down?
Before you applied the bog was there a layer of glass applied, or the only layer of glass is the final layer(s) which you feather into the existing board structure before routeing out the fin box holes?
^^^ Ah patience little grasshopper blocks are just resin and qcell. Boxes will have glass around them. Then glass over the top blending into the JP glass.
Mark board has never been repaired. Not my choice of material but hey if it works with the wood, then all good.
I'm trying to work out why. Pvc 80kg/M3 XPS 35kg/M3 wood ?kg/M3 normal board say total 3 layers of 160gm/m this board only 1/3 of normal glass layup.
I guess there is no right or wrong just different.
^^ I say it is wrong though as XPS tends to offgas and delaminate unless it is treated right (and the hurry hurry in Cobra will ensure it is not cut, offgassed under temp, then used....)
I'd love to see their advertising blurb from that year as the layup pics in the brochure re often very different from reality......
"Full carbon" - one strand end to end, patches under heels
lol
Mike, how thick is the blue stuff???
Stiffness varies with square of thickness, and I guess it's a 1:1 ratio with density. So if it's 5mm thick and 35kg/m3 it's going to be stiffer than 3mm of 80kg/m3. And the timber looks after the impact problems. It obviously works, and it could be lighter. 3x80 = 240, 5x35 = 175 + timber?
Select to expand quotedecrepit said..
Mike, how thick is the blue stuff???
Stiffness varies with square of thickness, and I guess it's a 1:1 ratio with density. So if it's 5mm thick and 35kg/m3 it's going to be stiffer than 3mm of 80kg/m3. And the timber looks after the impact problems. It obviously works, and it could be lighter. 3x80 = 240, 5x35 = 175 + timber?
Mike its 5mm thick same as the 5mm thickness i use on the bottom of boards, So as stiffness is related to the distance between the two skins dispite their density they would be the same stiffness, but one would be lighter and dent more easily hence the wood to stop dents and possibly resist compression of the outer skin when landing jumps. I googled pine "Radiata pine is commonly regarded as a 'medium' density softwood, with typical average tree basic density values of 400-420 kg/m3." Maybe the wood has better compression resistant properties than a thin layer of 160gm or 200gm glass. the wood looks to be between 0.5mm and 1mm thick.
Mark I've read about outgassing and epoxy not sticking well to XPS but the stuff is stuck pretty good. 2013 FSW
Select to expand quoteR1DER said..
Mark I've read about outgassing and epoxy not sticking well to XPS but the stuff is stuck pretty good. 2013 FSW
I've used XPS a bit and always had good adhesion, but the stuff was probably fairly old when I used it.
Stiffness not being related to density is counter intuitive. The core of the sandwich is in compression, so the denser it is the less it will compress, surely this increases sandwich stiffness, or is it just the point at which the sandwich fails under load?
What we are all forgetting is the blue Dow XPS has some Polypropylene incorporated into it somehow which is why we have so many delam issues. Its not just the outgassing but the PP. If you have ever tried to stick stuff to PP you would know its almost impossible.
What Cobra are using must be using is a true XPS manufactured for this purpose, not a foam dedicated for insulation purposes that board builders have stolen and tried to use.
I was dubious when i first saw that construction but i can't say I've heard of bulk failures (or any tbh), and its used more widely now across the JP range especially in the SUPS so it must be working.
When considering the stiffness of the veneer it acts like a layer of unidirectional since the fibres run pretty straight if the grain of the wood is true. Agreed its impact strength and ability to handle compression is key in its performance.
The thickness if the wood veneer has the effect of bulking up the outer laminate which we all know will increase compression strength and stiffness of the sandwich.
0.8mm of wood is worth about 600GSM of glass to get the same laminate thickness in a wetlay which would add considerable weight.
As Decrep says Stiffness is not related to density, it is actually related to the Young's Modulus Mike.
^^^ interesting about PP and never thought of that
Agree with the wood, I don't know why all waveboards don't have full wood, its so much stronger....
Now I imagine when JP went to XPS for the sandwich (1/4 the price of PVC foams) and wood (dirt cheap) they passed the cost saving on to the consumer?
lol
Select to expand quoteBertie said..
What we are all forgetting is the blue Dow XPS has some Polypropylene incorporated into it somehow which is why we have so many delam issues. Its not just the outgassing but the PP. If you have ever tried to stick stuff to PP you would know its almost impossible.
What Cobra are using must be using is a true XPS manufactured for this purpose, not a foam dedicated for insulation purposes that board builders have stolen and tried to use.
I was dubious when i first saw that construction but i can't say I've heard of bulk failures (or any tbh), and its used more widely now across the JP range especially in the SUPS so it must be working.
When considering the stiffness of the veneer it acts like a layer of unidirectional since the fibres run pretty straight if the grain of the wood is true. Agreed its impact strength and ability to handle compression is key in its performance.
The thickness if the wood veneer has the effect of bulking up the outer laminate which we all know will increase compression strength and stiffness of the sandwich.
0.8mm of wood is worth about 600GSM of glass to get the same laminate thickness in a wetlay which would add considerable weight.
As Decrep says Stiffness is not related to density, it is actually related to the Young's Modulus Mike.
Thanks Alex always good to have your composite and engineering knowledge on here. Do they need a layer of glass between the wood and XPS or could they have taken that layer of glass and put it on the outside and added to the other outside layer?
Select to expand quoteMark _australia said..
^^^ interesting about PP and never thought of that
Agree with the wood, I don't know why all waveboards don't have full wood, its so much stronger....
I'm thinking Bamboo laminate.
Infact I wonder how EPS bamboo XPS bamboo glass would hold up.
Here's a little jig I made earlier. To hold all boxes at tow and camber angles I want.
Select to expand quoteR1DER said..
Freehand routing, I know my lines are a bit wobbly.
Mine aren't any better.
But I get the best results dragging the router towards me, so my eyes, the line and the edge of the cutter are in the same plane
Sorry I didn't take pics of me resining the boxes in last week, my mobiles battery had run out and it was charging when I was doing the boxes so no pics. I basically wet out some 4oz cloth to wrap around the box plus some resin and qcell mixed up fill space, mixed a total of 120ml resin. Let it dry ground off excess, left a few air bubbles.
Today mixed 45 ml resin wet out 3 layers 4oz on plastic also mixed some of same batch with qcell to bog up air holes, layed glass over boxes squeegeed down left to dry. 1st layer meets up with boards sanded layer.
Mixed 30ml resin and 60ml qcell squeegeed on as a filler coat. Most of it will be sanded off.
