@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
Making skiing Green.