How do I determine needed core thickness for a new design?

[Docta]

Hey, first I want to say what and awesome site this is, Ive been poking around for awhile and am gearing up to try my luck at pressing a few skiis.

I have a heated press under construction and have been designing some skiis that I want to build. Ill be building several models between 140-180 cm with waists between 80 and 130 underfoot. I am going with sidewall constuction, 220z bottom and top glass.

I dont want to spend all the time to make core templates and spend all the money and time making skiis that are too pliable of to stiff, so was wondering how I get the right core profile for the stiffness I need?

Is cross sectional volume of wood a good indicator of stiffness? I imagine the cores on a 130 waisted model need to be much thinner than on the 80 waisted model.... any help in this matter would be greatly appreciated.

[powderho]

I dont want to spend all the time to make core templates and spend all the money and time making skiis that are too pliable of to stiff, so was wondering how I get the right core profile for the stiffness I need?

Classic! Ya I don't want to make skis that suck either. You will soon learn that this is the biggest variable to ski building. It sounds like you want to build just about every type of ski as well. For my personal preference....a ski that's 130 under foot will have an entirely different flex pattern than a ski that's 80 under foot. Even if they are both 2mm tip - 11mm waist - 3mm tail. My suggestion is to stick with one size at first. It will take a few pair to get the flex dialed in. Then move on to another size. Make a planer crib, or router bridge, that's solid and adjustable. That way you can adjust the thickness in a more controlled manner from core to core. A few of my skis have been a bit too stiff right in front of toe piece. You want to be able to adjust the thickness throughout the entire ski; not just the tip, waist, and tail. I made 3 sets of cores for my first pair. I had never seen a ski core not inside of a ski before. I really didn't have any idea of the flex they would produce. They turned out way too stiff. They shred the crud, but don't float in the pow. Don't expect your first pair to be perfect. They will probably still be fun to ride, but you will always be trying to perfect them. Good luck!

[doughboyshredder]

I am lucky enough to have access to a lot of different boards that I have ridden, so I measured all of those and kind of came up with a base line, which so far seems right on. Somewhere around here there is a spreadsheet for skis with some sort of predictions.

[Docta]

Yeah I know this is topic is the most frequent discussed on here, I have spent a good ten hours reading on it but Im looking for guideline or calculations on how width of ski relates to flexibility... will the stiffness of a laid up ski with a waist of 80 cm be 2/3 that of one at 120, so for the same flex characterictics, make the skinny ski 12 mm thick vs 8 on the fatter one so they have the same cross sectional area.? I doubt its a linear relation, as the distance between the fiberglass increases as well, so I assume a some percentage reduction must be factored in, like 50%, so for the same flex a difference of 2mm would make the 80cm waisted ski and 120 cm wasited sjki flex about the same. I would rather figure this out and find a way to make a nice constant flex with out building five sets to get close to what I need. I already got the variable router bridge under construction, I just dont want to wear it out on my first set.

[MontuckyMadman]

everyone asks for a formula for this, best we know of is here.

http://www.skibuilders.com/phpBB2/viewt ... highlight=

[MontuckyMadman]

howz bout here?
http://www.mediafire.com/file/w2zhdmuzk ... mmsexe.xls

[Docta]

Awesome. Thanks, thats pretty much what I was looking for.

[MontuckyMadman]

word now you have to tell me what all that crap means! LOL!