Balsa core fattys, first try!

[White Thrash Wednesday]

Aha!
So your the guy to challenge for the weight watcher title!
Could you tell me a little more about the construction and how the ski worked out "riding-wise"? Do you have any tips on losing a little weight without sacrificing performance? Do you feel there are any downsides to lighter skis?

I´m thinking full woodcore with wood side walls, carbon face sheets and wood faneer as top sheet for my concept skis. Haven´t decided if a should do a torsion box or sandwich yet... Something like 160-130-145 mm width and it will be 185-190 cm in length.

[MontuckyMadman]

No, the ski was too soft and had no dampness. Great in teh pow and I skied them all year. I used the west system and completely pressed all the resin out of the ski, unintentionally, heat cure at 60 psi.
Just poplar wood core and tip and tail spacer. Wood veneer topsheet.
19oz triax and a core dim at 1.5-11-1.7.

I added another diamond power band of triax and a new topsheet and used the super sap and added almost another pound between them.

Most of our fattys in the 185cm range are about 6.5 pounds per pair so under that could happen but tough. Aspen would do it but they would be soft.
Now 2.4lbs per ski is a different story.

[Brazen]

I started to tell you but never mind. I'm not sharing because hey, it's YOU. But...it's one word, starts with a t. Works to reduce 2 lbs off those pigs your building. I'm just sayin'...vapor light and 4 x's stronger with better behavior. K shhhhhh.......poplar cores SUCK! Real wood and ...Okay...shhhh be quiet....HEY! Certainly is weather we're having ). Wait..."diamond power band of triax"?. Really? Hahahahahahahahahahahhaaaaa. Good god. Remind me never to...hahahahahahahaha OMG. I apologize in advance for my comments. Hahahahahahaha! I can't stop laughing. Sorry guys. There's just a whole lot more stuff. I'm just going to be over here zipping my head. K shhhh hahahahahaha. Don't hit me hahahahahaha

[White Thrash Wednesday]

@Brazen

I don´t understand your post, and don´t know if your comment was intended for me. But I´m from Sweden and English is not my native language... I´m genuinely interested in building skis and I know there is a lot of knowledge here on the forum. Being able to discuss different ideas is what I think makes Skibuilders such a great place.

Would you mind expanding you comments? What mysterious "t" will help me reduce weight and enhance the performance? Why do poplar suck as core material? As far as I have found out poplar has good mechanical properties when compared to the density of the wood.

What "diamond power band" is, I have no clue. Strips of glass fiber triax used for further reinforcement?

If you don´t want to post you reply here, feel free to send me a message. I want to learn and hear your opinion of how to build durable light weight skis and all help I can get is greatly appreciated.

Thanks.

/Johan

[MontuckyMadman]

I started to tell you but never mind. I'm not sharing because hey, it's YOU. But...it's one word, starts with a t. Works to reduce 2 lbs off those pigs your building. I'm just sayin'...vapor light and 4 x's stronger with better behavior. K shhhhhh.......poplar cores SUCK! Real wood and ...Okay...shhhh be quiet....HEY! Certainly is weather we're having ). Wait..."diamond power band of triax"?. Really? Hahahahahahahahahahahhaaaaa. Good god. Remind me never to...hahahahahahahaha OMG. I apologize in advance for my comments. Hahahahahahaha! I can't stop laughing. Sorry guys. There's just a whole lot more stuff. I'm just going to be over here zipping my head. K shhhh hahahahahaha. Don't hit me hahahahahaha

comments like these are unnecessary and unwanted. Go be a rude person somewhere else.

If you are not going to post something somewhat useful or even mildly intelligible don't waste peoples time here.

yes diamond shaped sections of triax to increase the stiffness. It works quite well.

[White Thrash Wednesday]

@MontuckyMadman

What is your idea behind doing a diamond shaped lay-up and not just a full layer or a lengtwise strip of glass to make them stiffer? Is it to increase bending stiffness or torsional stiffness? Do you have any pics to show how it looks?

Really like the fact that you are using a lot of wood and Super Sap in your skis. Nice to see someone else thinking "Green" when it comes to ski building :-)
/Johan

[K.Ström]

Hello guys! I thought i was supposed to get an mail then somthing happend here. But not whis time i guess...

White Thrash Wednesday: Im living in a smal village in wester dalarna caled Vansbro. About 300km on the way up to Sälen from Stockholm.
Im also going to use Vacuum bagging as my pressing method.
So a weight challange? Im up for it!

Agian, a lot ofthinking has been going on in my mind and i have ideas for at least 20 skis. As i sad, my goal is to get the pair under 3000grams. Just beacuse ive found that i like light skis. They feels more "playfull" in som sort of they. Even though, im a pretty big guy and should be able to handle heavy skis.
About that diamond layup. I have thought about that one to. But only for the lenght going fibers. This is because you do not need all the lenght going fibers all the way out to the tip as the ski should become softer at the tips. This will also help to reduce the swing weight.
Im now planning to use paowlounia as the main wood in my skis and hopfully its strong enought to mount the bindings into. And to get rid of even more swing weight i will use balsa stringers in the tips and tails.
The sidwalls will be out of p-tex 4000 base material. The left over from making the ski bases. I saw this on the elan boomarang skis and i think that will be a great idea.

[Eirik Hanes]

@ johan,

I am a 5th year "a little bit of everything" Engineer student, but i think i can say that my main focus is structural/mechanical engineering. (at least thats what i plan to work with in my master thesis).

regarding balsa, i don't need that much maybe 4 sheets of 1200 X 600 (but if you get it super cheap, and it's no hassle i might take more.)

@ everyone
I used Aspen in my first skis and they got a nice medium stiffness (dont have the mm/N numbers). I don't see a problem getting stiff enough skis regard less of which wood is used, i mean it's just to increase the thickness. I can see that you might get a problem with strength, but not stiffness.

And regarding weight, i am tiered of people sayin you can get skis that weigh 750 g each.. but oh yeah they're 150 cm long and 50 mm waist. Therfore lets introduce The Ski mass index (SMI) (inspeired by BMI :P) simply SMI = Ski weight / Ski area

If i where a ski producer i would also give a comparison of strength for my different models, i mean who wants a ski that breaks just by you looking at it...

And as you say Johan ski performance is key! you don't really need a light ski that is'nt good to ski. But also a lighter ski will be better for many types of skiing i think (eg. tree skiing).

Have any one tested goode skis? i've heard that they are'nt very good to ski.

[K.Ström]

The stiffness is not the problem with balsa. But there are a lot of other problems along the way to be solved with a pure balsa core.
Like, delam problems. This, i dont actually tink isnt that much of a problem. A least not from the bending forces on the ski. The most of the delam problem comes from that the balsa itself is to soft to hold back the bindings. Wich makes the bindings rip the upper composite layer apart from the balsa core.
Then we have the biggest problem i guess. The balsa may be to soft to be able to handle the compression forces between the 2 composite layers. This can be solved by using stringers of harder wood. Or maybe stringers of standing balsa?

Just some thoughts from me, not facts...

Edit: Spelling

[carlito]

Going to continue my earlier post.

You need to put in hard-points of some type to support inserts (snowboards) and take screws (skis). At first this seems like no big deal. You need to ensure that thicknesses are the same. Further, as someone earlier mentioned, the stress riser issue shows up here. You need to make nice scarfs or curves to distribute the stresses.

It is hard to pre-glue sidewalls to the core

Remember, the material has no inherent strength. If there is a problem (delam, core crush, void, etc.) it is going to break.

Why bother? 1: The stuff is light. really light. 2: It is easy to shape. Thickness routing/sanding is fast, and you can cut the shape out with a razor knife. 3: It drapes. Fits into the presses/cassettes easily.

Now for something of a disclaimer. I have been using balsa for years with good results. But I constantly think about switching to regular wood. Why? Because its getting to be more and more of a pain in the a** and it simply isn't that much lighter.

First, the pain bit. When I first started out I laughed at the chumps using regular wood. gluing up cores, cutting with big saws, the weight, jigs. This balsa stuff is way better. But now I'm not so sure. The exotic shapes of the insert blocks/screw retention plates and the need to interface them accurately with the balsa core is a huge pain.

Second, the weight. Yeah, the core is light. Frighteningly so. But you kind of need more structural materials to compensate for the lack of strength. Not much, but enough to ensure that you would never use, for example 19 oz. triax instead of 22 oz. Weight creeps up. You need to make sure, damn sure, there is enough glue on the top of the core. End grain balsa soaks in resin. Like a sponge. Is that enough? Is that spot a little dry? Better put on a little extra. The weight creeps up. By the time you are finished, is it lighter than a lightweight solid wood core? I don't know. Those stupid insert blocks/retention plates. What are they made of? Better be damn strong. Don't want screws pulling. What do I have in the shop? Some 3 mm baltic birch ply. 2 layers of that with some glass in beween should be awesome. Not too light though. The weight creeps up. Those plates, how big should they be? What bindings will I/customer use. Better make em big enough. You can always use another set of inserts, what's another inch? The weight creeps up. Is it lighter? I'm not sure.

There are a bunch of things you can do to mitigate the weight issues, but they all increase the pain in the a** factor. You can pre-coat or seal the core with a small amount of resin. You can carefully minimize binding retention/insert blocks. Utilize exotics to gain strength/stiffness without weight penalty. Costs skyrocket.

Recipe for a lightweight powder ski: base to top. Base; vds on edges; approx 6oz. carbon cloth, cut a +/- 45; 9 oz. carbon uni tip to tail; balsa core with very close block tolerences pre-sealed; 9 oz. carbon uni tip to tail; 6oz.carbon cloth +/- 45; do a nice job on the top layer of carbon and blow off the topsheet. Light, stealthy look, not too torsionally stiff. Expensive. Lots of work.

Have fun

[K.Ström]

@carlito
Interesting reading. But three questions pops up in my head straight away.
Do the balsa alone stand the compretion pressure that comes with the ski bends? Or do you use any other wood stringers in the ski?
Do you need that much carbon to create a enogh torsion rigid ski?

@everyone:
If you impregnates the glas/carbon with the correct amount of epoxy and then put it onto the core. Will the balsa dry out the compocite layer or will it keep the correct amount of resin?

[White Thrash Wednesday]

@K.Ström
Ok, so you are a bit away from where I´m located... I have been thinging about usin P-tex for sidewalls too. I´ve never undestood why you would need 1.5 cm if sidewalls. When you get the Paulownia could you report back how the boards look and maybe check the density? I´m going to use Paulownia too for a few test skis but the Bauhaus boards are way cheaper then the ones I´m ordering (from boardbuildingsupply.eu, kite board cores). Also the Bauhaus ones have the right dimensions. From what I have heard Paulownia have much better strength then balsa, but is still very light weight. Some say that it has the best specific (/density) mechanical properties of any wood.

I think the balsa will handle the compression without any problems if you use standing end grain balsa, but you have a very good point in that the low density of the wood will have low pullout strength for the binding screws. I think inserts will solve that. If infusion is done properly I don´t see why the facesheets would delam.

If you wet the fibers with the right amount of resin and then apply it to the core, the balsa will soak up a lot of the resin, at least if you have the balsa grains "standing". A least that happened to me during some test manufacturing with vacuum.

@Eirik
I have asked my friend to look into if we can get smaller amounts of balsa. I´ll get back to you as soon as a get more info. And yes, building a light ski is not a problem, but building a durable light weight ski is. I´m looking for high performance as well as low weight. But my guess is that a Fatty that is going to be used in only deep snow can be made softer than a piste ski and also is there need for any real torsional rigidity? I´m thinking that the "boundary" conditions for riding powder will be much more "soft" than riding in the piste "hard/clamped". If this is true, you could save some weight by skipping the [+45/-45] layers and just go with UD reinforcement.

@carlito
Thanks for the good info regarding your balsa skis! Seem like you have been working on this for a while :-)

[fa]

From what I have heard Paulownia have much better strength then balsa, but is still very light weight. Some say that it has the best specific (/density) mechanical properties of any wood.

i was looking for paulonia wood (kiri) in the local market without any luck, few years back when it came big in kiteboards cores.
i bumped on it accidentally when my sister asked help to remove a painting's canvas from its frame, so she may roll it for posting.
the back-frame was paulonia, very clean grain, super light, i weighted it ~250kg/m3 and very stiff.
i mean nothing to do with balsa stiffness, more or less something like poplar.
very interesting wood indeed.
i wanted to plant some seeds in front my sisters country house, but she wouldn't allow after reading it is rated as an invasive specie
meh, women...

[White Thrash Wednesday]

@fa
It´s going to be cool to try it for skicores. I know a few skibrands use it, but I´m not sure if they use 100% Paulownia or have stringers or mix it up whit other woodtypes. Should be good for holding screws to from what I have heard, and is not as sensitive to water as other wood types.

Going to try Spruce (gran?) as well :-)

[OAC]

Going to try Spruce (gran?) as well :-)

Works only for saunas! Too much resin (kåda) and knots. IMO.
But, since the "pallet project" worked, so nothing is impossible.