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Lightwind kiteboard build, planing ahead

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phuqit
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Re: Lightwind kiteboard build, planing ahead

Postby phuqit » Sat Jul 21, 2018 9:00 pm

rynhardt wrote:
Sat Jul 21, 2018 8:16 pm
1. Do you mean the rocker flattened out and bent the other way between the foot pads? 9mm thickness in the centre with 250gr carbon (0 deg, I assume) both sides should be plenty stiff, especially with some concave.
I mean that the board has an almost flat section in the middle, and it has a sharper bend closer to the area where I started thinning the profile, like 5cm off the straps, going to the tip ends. But as I said, it works just fine for a LW board, probably even better than the uniform rocker, or at least that's my impression. Also, I used 300gr biax (oriented corner-to-corner), and 250gr unidirectional, at 0 deg, per side. Actually, bending the cut-offs takes some effort, so I think using 200 uni + 200bi would be plenty for a wood core. Again, I was estimating the materials for a foam core board, and then got distracted... and went with wood. The weight of carbon + epoxy added significant weight to wood core (which was ~2kg), so the naked board is approx 4kg now (0,85m2 area covered by 550gr carbon x 2 + 100 proc epoxy weight...). So the way to reduce that would be to both reduce the core weight (by thinning it) and use thinner carbon. That way I am sure I can lose at least a kilogram of weight, perhaps more, since paulownia is even lighter than WRC. Anyway, I have to give it some more thought. The variables are there, just need to make sure I do the math correctly.
rynhardt wrote:
Sat Jul 21, 2018 8:16 pm
3. Depending on how expensive your ABS is, you can either cut strips and bend them, or cut the entire outline (see pic below). I've had good success with just an alcohol wipe,abrade, alcohol wipe regime for bonding the ABS. I haven't flamed it and my boards have held up fine so far.
I'll make some tests, worst case, I found some PU @ 75-80 Shore D here at reasonable prices: http://easycomposites.co.uk/#!/resin-ge ... resin.html, so I can go the downunder's suggested route and pre-make the rails in a mould. ABS I is less messy though.
rynhardt wrote:
Sat Jul 21, 2018 8:16 pm
4. My inserts are mounted inside an ABS rail (pic below). This was for my split board, so there's extra inserts in the middle which you can ignore.
Awesome, I like it. Question though, I see you use two layers of ABS sheet at the middle? This is for the split setup, right?
rynhardt wrote:
Sat Jul 21, 2018 8:16 pm
5. Machining with a belt sander takes enormous finesse.. lots of guys use a router instead. In the video below I use a router table with a profile.
Tell me about it :) There were a lot of those 'a little... a little more... f***!.. too much' moments, but hey, epoxy covers all the faults!
rynhardt wrote:
Sat Jul 21, 2018 8:16 pm
6. Yeah, your carbon layup would be fine with a foam core and is probably over specced for a wood core.
Just a stupid idea - if I were to use a 3mm AIREX C70-90 for the tips, and add extra 3mm layer for the center and pad area on top... Would it be workable? Also, do the beams, like Brokites do, to strengthen it. I am pretty sure the same amount carbon can take it...

phuqit
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Re: Lightwind kiteboard build, planing ahead

Postby phuqit » Sat Jul 21, 2018 9:55 pm

One more thing, junksupply has some isosport topsheets, namely, http://www.junksupply.com/product/pa-to ... 0mm-clear/

Does anyone have experience with it? I'm seeing scratches on the epoxy from riding it for just one day, so some kind of protective sheet seems to be a good idea. How/if at all would it work with the infusion? I imagine, if the core is scored properly, the epoxy would be able to get under the top/bottom sheet and wet out the layup, but I assume there are plenty of variables there. Also, provided I use an ABS rail, some wicked infusion scheme (like, vacuum pump at the center) would be best... I'll have to test it out guess.

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rynhardt
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Re: Lightwind kiteboard build, planing ahead

Postby rynhardt » Sat Jul 21, 2018 11:41 pm

phuqit wrote:
Sat Jul 21, 2018 9:00 pm
rynhardt wrote:
Sat Jul 21, 2018 8:16 pm
4. My inserts are mounted inside an ABS rail (pic below). This was for my split board, so there's extra inserts in the middle which you can ignore.
Awesome, I like it. Question though, I see you use two layers of ABS sheet at the middle? This is for the split setup, right?

Just a stupid idea - if I were to use a 3mm AIREX C70-90 for the tips, and add extra 3mm layer for the center and pad area on top... Would it be workable? Also, do the beams, like Brokites do, to strengthen it. I am pretty sure the same amount carbon can take it...


4. My board is 10mm thick in the centre, 5mm on the edges. I used 5mm ABS sheet, so single layer for the rails (5mm) and double layer for the "spine" (10mm) where the inserts are. Inserts are approx 5mm high, so only the top layer of the spine has cutouts for the inserts. I also use centre fins (i.e. not at the edges of the board), for which I drill holes into the spine afterwards.

5. You can easily glue layers of foam together to add thickness, yes. I do this on my wakeskates to take the edges to 30mm (two layers of 15mm foam). You will however still need to blend the top layer into the bottom layer so there isn't a sharp step change, which will cause a stress riser in the fibres. Not sure if using two layers is going to be any easier at the end of the day..

I've seen the Brokites process, but until I can ride one of their boards and feel a difference, it just looks like extra work.

phuqit
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Re: Lightwind kiteboard build, planing ahead

Postby phuqit » Sun Jul 22, 2018 12:02 am

My problem is with thinning the edges uniformly, for the center area I can just smooth it by hand without compromising the whole outline.

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rynhardt
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Re: Lightwind kiteboard build, planing ahead

Postby rynhardt » Sun Jul 22, 2018 12:05 am

phuqit wrote:
Sat Jul 21, 2018 9:55 pm
One more thing, junksupply has some isosport topsheets, namely, http://www.junksupply.com/product/pa-to ... 0mm-clear/

Does anyone have experience with it? I'm seeing scratches on the epoxy from riding it for just one day, so some kind of protective sheet seems to be a good idea. How/if at all would it work with the infusion? I imagine, if the core is scored properly, the epoxy would be able to get under the top/bottom sheet and wet out the layup, but I assume there are plenty of variables there. Also, provided I use an ABS rail, some wicked infusion scheme (like, vacuum pump at the center) would be best... I'll have to test it out guess.
I order my bottom sheet from junksupply, but this is a transparent grind base and it works well with infusion provided your core is full of holes and you've got channels.
It's however difficult to get proper resin distribution with a topsheet with infusion. The flow is not the problem, (so yes, you would have resin channels in the top as well), it's the bubbles.

With flow mesh any bubbles (whether entrained or due to resin reaction) just flows up into the flow mesh and out of the laminate, so you get a super solid laminate with no voids.
Put a non-permeable membrane on top (like a TPU topsheet) and the bubbles have nowhere to go - the resin flow is typically not fast enough to move them along. You could potentially try infusing the board with the rocker table on its side, so the exit tube is on top - this way gravity might help get the bubbles out. We considered doing this at some point but have resorted to just using flowmesh on top.
Final prep is typically paint and sand and paint again. Painting a solid laminate with a peelply finish is a joy. Painting a laminate with voids and pinholes is a freakin nightmare.

If you find your epoxy scratches easily, it may benefit from a high-temperature post cure. Something like 16 hours at 50C will make a significant difference.
Go check your resin's datasheet, it should have a post-cure schedule with the post-cure properties.

Lastly, I do cut 1mm deep channels into the ABS rails every 2cm (with a hacksaw blade), in order to promote resin flow.

PS. The good and the bad thing about topsheets is that they hide any imperfections. So if you have dry patches below the topsheet, no-one will know... until the board snaps.

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rynhardt
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Re: Lightwind kiteboard build, planing ahead

Postby rynhardt » Sun Jul 22, 2018 12:11 am

phuqit wrote:
Sun Jul 22, 2018 12:02 am
My problem is with thinning the edges uniformly, for the center area I can just smooth it by hand without compromising the whole outline.
If you use foam, then a sanding block with some 40grit will make short work of shaping, by hand.

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downunder
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Re: Lightwind kiteboard build, planing ahead

Postby downunder » Mon Jul 23, 2018 3:33 am

phuqit wrote:
Sat Jul 21, 2018 9:00 pm
.
.

So the way to reduce that would be to both reduce the core weight (by thinning it) and use thinner carbon. That way I am sure I can lose at least a kilogram of weight, perhaps more, since paulownia is even lighter than WRC. Anyway, I have to give it some more thought. The variables are there, just need to make sure I do the math correctly.
.
.
Just a stupid idea - if I were to use a 3mm AIREX C70-90 for the tips, and add extra 3mm layer for the center and pad area on top... Would it be workable? Also, do the beams, like Brokites do, to strengthen it. I am pretty sure the same amount carbon can take it...

The math is clear. Stiffness depends on the thickness cubed so a 20% increase translates into 50-70% increase in stiffens if not mistaking. Hence, adding fibers to compensate is a waste coz the core itself is lighter than the added laminate. And cheaper.

If you are 100kg the wood core should be 15-18mm in the middle. That is a huge increase in stiffness from 9mm core. I would argue with 18mm core, glass it with only 200g FG UD on top/bottom and will never break. But glass 9mm core with whatever, it might buckle and break.

~

The reason they are doing it is a foam. Foam has no strength like wood. And no, the tips on production boards are not closed cells, I think. But 2-3mm thick PU or similar sheet which is easier to handle and shape.

D.

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Re: Lightwind kiteboard build, planing ahead

Postby phuqit » Tue Jul 24, 2018 10:38 pm

Alright, so we've finally properly tested the board. The wind was 8-20 knots, all rider weights (60kg to 110kg), all kinds of kites (8 to 21m), and skill levels (instructors and noobs). So far, the feedback is surprisingly good! The board is quite stiff, comparable to F-One TRAX carbon version, and not that much flex. Which is ok for a lightwind board though. The XCR epoxy from easycomposites I covered the board with actually looks quite awesome, and after I've left it in the Sun for a couple of days to cure with bbq thermometer attached, seems to be much stronger, and doesn't wear as much.

So we'll be starting with the new build - the current one will remain in the inventory as-is, until it breaks. I'll be using a 2mm ABS plastic sheet for the edges now, and will CNC the shape, so that we can get a repeatable build. I'm not so impressed with the flanged nut inserts, so I'm wondering if anyone had some experience with Brokite "failsafe" inserts:
https://www.youtube.com/watch?v=HRb3KYw0S-g

This actually looks like a decent and clean way to make them. The problem I have here, ABS rods are nowhere to be found in the EU, and plastic sheet on demand is only available in 2mm thickness locally. Are there any plastics which are comparable to ABS strength-wise, and will bind with epoxy when laminating? I'm aware some of them require sanding/flaming to bind. Any advice?

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rynhardt
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Re: Lightwind kiteboard build, planing ahead

Postby rynhardt » Wed Jul 25, 2018 1:02 pm

phuqit wrote:
Tue Jul 24, 2018 10:38 pm
Alright, so we've finally properly tested the board. The wind was 8-20 knots, all rider weights (60kg to 110kg), all kinds of kites (8 to 21m), and skill levels (instructors and noobs). So far, the feedback is surprisingly good! The board is quite stiff, comparable to F-One TRAX carbon version, and not that much flex. Which is ok for a lightwind board though. The XCR epoxy from easycomposites I covered the board with actually looks quite awesome, and after I've left it in the Sun for a couple of days to cure with bbq thermometer attached, seems to be much stronger, and doesn't wear as much.

So we'll be starting with the new build - the current one will remain in the inventory as-is, until it breaks. I'll be using a 2mm ABS plastic sheet for the edges now, and will CNC the shape, so that we can get a repeatable build. I'm not so impressed with the flanged nut inserts, so I'm wondering if anyone had some experience with Brokite "failsafe" inserts:
https://www.youtube.com/watch?v=HRb3KYw0S-g

This actually looks like a decent and clean way to make them. The problem I have here, ABS rods are nowhere to be found in the EU, and plastic sheet on demand is only available in 2mm thickness locally. Are there any plastics which are comparable to ABS strength-wise, and will bind with epoxy when laminating? I'm aware some of them require sanding/flaming to bind. Any advice?
I use the inserts from junksupply - pic below. You can also get some other nice supplies from them.
ABS can easily be plastic welded with methyl chloride, so with you can have 2 layers of 2mm welded together to make 4mm for example.

I looked at your XCR epoxy, and it will definitely improve with post-cure - the images below I snipped from the XCR datasheet.

If you want to get the best from your resin system don't skimp on the post-cure. :!:
Attachments
properties.PNG
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kiteboard-ski-and-snowboard-inserts-300x277.jpg
kiteboard-ski-and-snowboard-inserts-300x277.jpg (10.15 KiB) Viewed 494 times
fullcure.PNG
fullcure.PNG (74.02 KiB) Viewed 494 times

fluidity
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Re: Lightwind kiteboard build, planing ahead

Postby fluidity » Sun Sep 02, 2018 2:24 am

phuqit- I use these: https://www.anzor.co.nz/nuts/tee-nuts

8mm thread size you can prep for with a 20mm spade bit.
I've had no failures yet.


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