i favor spruce as i have plenty of low quality 3x5cm drying in my balcony
strong and smelly
hard to find clean planks without any nodes though
once i left a spruce kiteboard in the car under full summer sun for a day and the next morning a teardrop of wood resin appeared on top of the top skin just above a damned node
how the hell it was squeezed through the fg and the epoxy, i guess it must have boiled in there
gran is the scandinavic tree? whats its density like?
Balsa core fattys, first try!
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White Thrash Wednesday
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- Joined: Wed Dec 15, 2010 1:42 pm
- Location: Stockholm, Sweden
But, Swedish Spruce="Gran" have a Youngs modulus of up to 16.5 Gpa with a density of ~ 400 kg/m^3... Seriously stiff wood when compared to its weight. Stiffer than UD glass fiber which is about 40 GPa (volume fraction 0.5) with a weight of 1800-2000 kg/m^3.
Mother Nature is a clever engineer with many years of working experience ;-)
Mother Nature is a clever engineer with many years of working experience ;-)
Making skiing Green.
Answering Questions
@ Kstrom
First question: The balsa is strong enough. Stringers are unnecessary. Keep in mind that I am referring to end grain balsa. You also have to remember that the bindings are a big stress riser. Some sort of core rienforcement will be needed to avoid this. Same goes for voids/dry core. These are guaranteed failures. Avoid at all costs.
This leads to the third question: Getting the correct fiber/resin ratio into facings and then applying to the core. I would not try this. Especially with balsa. Threee reasons. First, its really hard to get the "correct" fiber/resin ratio with a hand lay-up, try to do the best you can, and its probably workable. Remember the old adage: Too much resin is heavy, not enough will break. Your choice. Second the balsa will soak up a surprising amount of resin. I will assume here that you were talking about having the core dry, and putting the wet laminates onto it. You really need to wet the core out to make sure. This problem becomes especially acute if you use any heating. The elevated temperatures will cause the resin's viscosity to drop (get much thinner) allowing it to soak even more effectively into the core. Finally, resin control is always an issue. Once the vacuum is on/press is on it becomes a sort of black box. It's really hard to tell what is going on in there. As the resin heats up and gets thinner, and as the pressure comes on it gets really easy to squeeze out/bleed out too much resin. This can be hard to see, even when the skis (board) are done. It seems really nice and light though. Problem come later, high pressure spots (the end of the edge contact zones and end of tips/tails, or interfaces with tip/tail fillers or other core rienforcements) may delaminate pretty easily. Edges seem to pull out really easily. topsheets delam. I believe that this is probably the biggest quality issue most people will have once they deal with the "getting a usable pair of skis out of this" stage is over. My two cents says avoid resin dry layups. You can wet the materials out somewhere else and apply onto the press/cassette, that's fine, just not to anything dry.
As to the carbon. a layer of 6 oz cloth (0/90 cut at 45, spun 45 to get fibers at +-45) only gives you 3 oz in each torsional direction. 22oz triax and 19 oz triax (the industry benchmark) provide 6 oz of glass in either direction. Even in a pow ski you need some sort of torsional stiffness (how much is a whole other can of worms), so half the weight to get somewhere around the same stiffness is a pretty good trade. It definitely would not be too torsionally stiff. The best stuff I have made yet uses 6 oz of carbon in each torsional axis. The grip is nice, and it doesn't affect the lengthwise stiffness at all.
Hope this helps.
Ps. im new to the forum thing and don't really know the etiquette involved. Are these posts too long/rambling?
Have fun,
Carlito.
PPs. Just snowed 45 cm in 36 hours. -10 C. Pow skis working great. still snowing
First question: The balsa is strong enough. Stringers are unnecessary. Keep in mind that I am referring to end grain balsa. You also have to remember that the bindings are a big stress riser. Some sort of core rienforcement will be needed to avoid this. Same goes for voids/dry core. These are guaranteed failures. Avoid at all costs.
This leads to the third question: Getting the correct fiber/resin ratio into facings and then applying to the core. I would not try this. Especially with balsa. Threee reasons. First, its really hard to get the "correct" fiber/resin ratio with a hand lay-up, try to do the best you can, and its probably workable. Remember the old adage: Too much resin is heavy, not enough will break. Your choice. Second the balsa will soak up a surprising amount of resin. I will assume here that you were talking about having the core dry, and putting the wet laminates onto it. You really need to wet the core out to make sure. This problem becomes especially acute if you use any heating. The elevated temperatures will cause the resin's viscosity to drop (get much thinner) allowing it to soak even more effectively into the core. Finally, resin control is always an issue. Once the vacuum is on/press is on it becomes a sort of black box. It's really hard to tell what is going on in there. As the resin heats up and gets thinner, and as the pressure comes on it gets really easy to squeeze out/bleed out too much resin. This can be hard to see, even when the skis (board) are done. It seems really nice and light though. Problem come later, high pressure spots (the end of the edge contact zones and end of tips/tails, or interfaces with tip/tail fillers or other core rienforcements) may delaminate pretty easily. Edges seem to pull out really easily. topsheets delam. I believe that this is probably the biggest quality issue most people will have once they deal with the "getting a usable pair of skis out of this" stage is over. My two cents says avoid resin dry layups. You can wet the materials out somewhere else and apply onto the press/cassette, that's fine, just not to anything dry.
As to the carbon. a layer of 6 oz cloth (0/90 cut at 45, spun 45 to get fibers at +-45) only gives you 3 oz in each torsional direction. 22oz triax and 19 oz triax (the industry benchmark) provide 6 oz of glass in either direction. Even in a pow ski you need some sort of torsional stiffness (how much is a whole other can of worms), so half the weight to get somewhere around the same stiffness is a pretty good trade. It definitely would not be too torsionally stiff. The best stuff I have made yet uses 6 oz of carbon in each torsional axis. The grip is nice, and it doesn't affect the lengthwise stiffness at all.
Hope this helps.
Ps. im new to the forum thing and don't really know the etiquette involved. Are these posts too long/rambling?
Have fun,
Carlito.
PPs. Just snowed 45 cm in 36 hours. -10 C. Pow skis working great. still snowing
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MontuckyMadman
- Posts: 2395
- Joined: Fri Jun 20, 2008 9:41 pm
http://www.tetongravity.com/forums/show ... p?t=211200191 Fats are just awesome. 116 underfoot, same profile, same flex in the tip but beefier in the tails. 4.8lbs.
These are aspen btw.
I bet a 12 oz carbon roving and...
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White Thrash Wednesday
- Posts: 30
- Joined: Wed Dec 15, 2010 1:42 pm
- Location: Stockholm, Sweden
@Madman
Is the weight per ski or pair? Didn´t find out that in the link. Maybe I missed it...?
@Carlito
I thought your reply was really good and informative. Keep up the good work! Your reply sort of sums up my experience of working with balsa, vacuum and applied heat for curing :-)
/Johan
Is the weight per ski or pair? Didn´t find out that in the link. Maybe I missed it...?
@Carlito
I thought your reply was really good and informative. Keep up the good work! Your reply sort of sums up my experience of working with balsa, vacuum and applied heat for curing :-)
/Johan
Making skiing Green.
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MontuckyMadman
- Posts: 2395
- Joined: Fri Jun 20, 2008 9:41 pm
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White Thrash Wednesday
- Posts: 30
- Joined: Wed Dec 15, 2010 1:42 pm
- Location: Stockholm, Sweden
-
White Thrash Wednesday
- Posts: 30
- Joined: Wed Dec 15, 2010 1:42 pm
- Location: Stockholm, Sweden
The other day I got hold of some Paulownia from boardbuildingsupply.eu. I only weighed one board but the density was approx. 300-330 kg/m^3 so it was not as light weight as I expected. Info on Paulownia often states that it is somewhere in the 200-250 kg/m^3 region.
I´m looking at end grain balsa too which is 155kg/m^3 (ProBalsa from DIABgroup.com). One concern with the end grain balsa sheets is that it has virtually no stiffness in bending, so if the facesheet fail, the ski will snap. But it will be light ;-)
/Johan
I´m looking at end grain balsa too which is 155kg/m^3 (ProBalsa from DIABgroup.com). One concern with the end grain balsa sheets is that it has virtually no stiffness in bending, so if the facesheet fail, the ski will snap. But it will be light ;-)
/Johan
Making skiing Green.
I've been using Paulowia in the place of Balsa in Surfboard building. It has a really high strength to weight ratio and now is farmed in the states(South Carolina) so the cost is way better. Plus it can be bought in raw form and you're able to pick tighter grains from different parts. We use them in Tow-Board surfboards(50 foot + wave range) and have had know problem with breakage. And we are only glassing with 8 oz bottom and 8oz top. The wood provides a good flex ratio as well. I never thought about using it in snowboard/ski building. May give it a try as I think we still have some. Hummmm!? keep ya posted.
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doughboyshredder
- Posts: 1354
- Joined: Mon Sep 17, 2007 7:37 pm
not rovingMontuckyMadman wrote:http://www.tetongravity.com/forums/show ... p?t=211200191 Fats are just awesome. 116 underfoot, same profile, same flex in the tip but beefier in the tails. 4.8lbs.
These are aspen btw.
I bet a 12 oz carbon roving and...