Balsa core fattys, first try!

chrismp · Post by **chrismp** » Wed Jan 05, 2011 3:11 pm

check if there are any Bauhaus hardware stores in your country. they sell it at a great price (about 12 EUR for a 200x30x1,8cm board). another good thing about paulownia is that it has virtually no knots.
if you can't find it, i could send you some...just let me know and i'll get you a shipping quote.

you'll need a denser wood under the bindings though. paulownia is pretty soft.

edit: just found this http://www.bauhaus.se/
if they don't have it in store they should be able to order it

K.Ström · Post by **K.Ström** » Thu Jan 06, 2011 1:12 am

Yepp, we do have bauhaus. But its a few km away. And I cant find it on there webbpage. I will try calling them tomorow to se if they have any.

Just for fun, could you check the shipping quote? Cause this material sounds interesting and im really want to get started with my first pair of skis asap.

Jibber · Post by **Jibber** » Thu Jan 06, 2011 3:10 am

Right now I am building a kiteboard with Paulownia wood from Bauhaus. The problem is that the Paulownia board tends to wrap because it is glued together from only three stripes.

I think I will cut the board in thinner stripes and glued them together again to avoid the problem for the next time.

The price for the wood is really good!

@ chrismp: Did you run across the same problems and what is your solution?

Cheers, Christoph

chrismp · Post by **chrismp** » Thu Jan 06, 2011 6:07 am

@Christoph: well, we buy the size of board i mentioned above. in this size they come as full wood and not strips glued together.
what we do is glue about 17 of these boards together to get a big block and then we slice off the final cores with a bandsaw.

@K.Ström: cheapest shipping option i could find was about 32 EUR. this is a fixed price, so it stays the same up to the packet size limitations (300cm for girth+longest side) and a maximum weight of up to 31,5 kg. means i could easily send you e.g. ten boards at the same price. (i'll have to check out what one of these boards weighs...but just with the size limits i could send you up to 36 boards

)

If anyone else in Europe needs some paulownia, i'm happy to send you some! (btw 32 EUR is the highest price for Europe since Sweden is pretty far away...the prices for other countries vary from 21 EUR up to 32 EUR)

K.Ström · Post by **K.Ström** » Thu Jan 06, 2011 11:48 am

32euros is a fair price for shipping. I guess 5boards will be enought for me cause i dont have any more time to do skis this winter. And i want to test other materials as well.
So i would love to have some cores from you. How do i pay you. Do you have any paypal account?

SleepingAwake · Post by **SleepingAwake** » Sun Jan 09, 2011 10:17 am

hello guys

if you really wanna build a board with a balsa core i would highly recomend the use of end-grain wood. think once of the direction of the forces and the demands on a core. the main function of the core is to hold together the upper and the under laminate. end-grain wood has the same positive properties of honeycomb, but it ist much stronger because there are no gaps in it.

we use it now for a long time for kiteboards:

aloha, reto

White Thrash Wednesday · Wed Jan 12, 2011 1:53 am

@K.Ström
Hej!
Where are you located in Sweden by the way? I have been thinking about balsa wood in skis for awhile. I have done some sandwich work using balsa as core material and it worked fine. Among other things the load bearing chassie for the bio-based car "Aurora", made from beans, hemp and balsa :-)

What manufacturing method will you be using? We used vacuum infusion. Since the grain is open the core will absorb some resin and making the ski heavy. This could also be the cause for delamination if the resin is absorbed by the core instead of acting as a adheasive between the face sheet and core. We did some experimenting with balsa and prepregs ad it seemed that the resin in the prepreg got absorbed by the core and the face sheets could easily be peeled off... So what we did was to add a thin layer of resin just by hand on the balsa and let it cure to seal the grain. Then did the infusion part as usual. It healped with the "soaking" issue. We were using end grain balsa, supplied by Diab Group here in Sweden.

End grain balsa have good mechanical properties in compression so it should work as core material for skis, but I think you need to consider the fastening of the bindings due to the low density of Balsa. Maybe insert could be an alternative to having hardwood underfoot? The different stiffness of the two types of wood could cause problems due to stress concentrations. I also visited the Extrem factory in Såå last spring and they did some experimenting on using balsa stringers (with the grain lengthwise), don´t now how they held up but they were really ligth! Approx. 1500g/ per ski. I think they had a 95 mm waist.

If you want really light skis you could consider foam (also supplied by Diab) I think the foam have closed cell structure and that will lessen the problem with soaking, although I think balsa have better compression properties. (data sheets with mechanical properties for balsa and foam core materials are avaiable on the Diab web site)

My 0.02€...

Hopefully I will do an attempt to make my own light weight fatties (160-130-140 mm) so the game is on for the <3 kg/pair challange ;-)

Ohh! I´m also interested in the Paulownina blanks. Maybe I can order a few with you K.Ström and we share shipping cost? Or did you call Bauhaus here in Sweden to see if they could order it?
/Johan

chrismp · Post by **chrismp** » Wed Jan 12, 2011 2:27 am

well, so far K.Ström wants 5 boards of the 300x2000x18mm size. i'm going to buy them today, so you'll have to be quick...unfortunately i dont have his phone number.

White Thrash Wednesday · Wed Jan 12, 2011 2:47 am

Ok! I called around to the Bauhaus´s here in Sweden and they never heard of Paulwonia boards ,or the wood species for that matter, and couldn´t order from Germany either...

Since I dont´t now where K.Ström is located I´ll pass. Domestic shipping in Sweden is generally very expensive... But thanks for the offer anyway :-)

/Johan

Eirik Hanes · Post by **Eirik Hanes** » Wed Jan 12, 2011 3:19 am

I see you participated in the shell eco-marathon as well, awesome!

We used some divinycell in our car:

But it was completely packed in in carbon fiber (like a cap ski kind of), which makes it much stronger.

But the race for a 3kg/pair fatty is definitely on! I have some nice quadaxial Carbon i plan to try out.

I did make a comparison chart for balsa, divinycell and some regular woods, I'll see if i can translate it and post it here.

I am also wondering about what to do around the bindings, maybe using some long inserts that glue together withe bottom composite layer will be strong enough?

Eirik Hanes · Post by **Eirik Hanes** » Wed Jan 12, 2011 3:30 am

@ johan,

We could maybe share a box of probalsa from diab, it costs like 3500 nok +tax(25%) for like 15 m2 (they would not sell smaller quantities). but i guess it might be a bit much hasle with shiping and every thing. but if you plan to go to norway to ski we could maybe work something out.

The skiing in norway is great at the moment btw, lots of snow

White Thrash Wednesday · Wed Jan 12, 2011 8:26 am

@Eirik

What a coincidence! I took part in the Eco Marathon in 2009 with team KTH :-) So what is your backgroud Eirik, have you studied Light weigt structures as well?

One box is a lot of balsa... Let me see what i can do about that. I have a friend of a friend of a friend (sort of) who i still think work for DIAB. I´ll make some calls and see if it is possible to get some "leftovers". How much do you need?

Cool that you dared to join the light weight fatty build-off as well ;-)
I wonder how much just the edges, base,fiber, resin and topsheet weighs for a par of fatties, probably not many grams to spend on the core before we reach 1500g, but problems are ment to be solved right?
/johan

powderho · Post by **powderho** » Wed Jan 12, 2011 9:00 am

Eirik Hanes wrote: But the race for a 3kg/pair fatty is definitely on!

I would be willing to bet Goode skis has already done this. Maybe not 130mm in the waist but close. Mr. Goode himself told me he ads weights as ballasts to the tips and tails to make his skis more stable, and they are still sub-8 lbs. Interesting skis, interesting guy to say the least. But come on, foam cores?!!! No way these skis can withstand the abuse of even an average local skier in Little Cottonwood though. When they fail, they really fail. They just snap in half.

White Thrash Wednesday · Wed Jan 12, 2011 11:38 am

@powderho

Dude, You´re no fun. Don´t spoil our vision ;-)
Yes, you are correct. According to Goode:

"A typical 175cm GOODE ski weighs only 2.1lbs. (950gms)" and then we have http://www.skitrab.com

Where the lightest skis are about 750g! These skis may not have the same width but still, it is some serious weight watcher skis :-) A real challenge for me is to build my OWN lightweight skis, not go out and buy them (it´s OK to quote me on this when my finished skis probably end up weighing 3 kg each ;-) . Where is the challenge in that? I don´t think the foam core itself is the problem its used in many more demanding applications than skis, like aerospace. The trade of for low weight will sacrifice some durability. So how light is light enough to still take the abuse of real riding?

It is possible that a somewhat stiff 1.5 kg Fatty ski is not possible to build with a wood core, at least not a 180-190cm ski with a 120mm waist. Maybe all the materials except the core will weigh more than 1500g... That we will probably find out in the near future :-)

MontuckyMadman · Post by **MontuckyMadman** » Wed Jan 12, 2011 12:43 pm

I made a pair in poplar 186 140-120-130 at 6lbs per pair.
I don't know what you guys are talking about.

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Balsa core fattys, first try!