Hey Guys
I'm a skier myself and built quite a few skis and know what i do there. But i would love to make a snowboard for my niece as a christmas gift and need some pointers as i have no clue how stiff a snowboard for a 8 year old girl should be. Anyone who can give me a starting point with a core thickness and and a basic layup so I have a base to work from for my calculations?
Thanks in advance
I would guess 4-5mm for core thickness. For reference I am 215lb and ride a board with a 7mm poplar core. I would also explore using a softer wood, too. I think some kids boards may even have partial foam cores.
Yeah that was my gut feeling too. What do you think about the layup?
I might just end up making a board 1/3 of the stiffness of an adult board for 1/3 of the rider weight. Kind of makes sense i guess?
Even tho the surface area of a kids board is more than 1/3 of an adult one so not quite convinced it scales this easily...
The only problem I see with really thin cores is the very small inserts you will need and they will only have three turns on each screw.
I would think about 450gsm glass with only 45/45 degree tows.
Then a 6mm core will still be plenty flexy.
1/3 the stiffness for 1/3 the rider makes sense to me. But scaling dimensions is not the only means to get there, plus it runs you into insert problems like mentioned.
If I may nerd out a little bit, allow me to reference beam theory. https://en.wikipedia.org/wiki/Bending_stiffness
Let's assume your niece is popping an ollie (rad), and applying a moment to the board. We're guessing that that is 1/3 the moment an adult rider would generate. In order to get a proportional amount of pop, you'd want to adjust stiffness such that you get the same amount of beam curvature (k).
M = EIk
The term "EI" is your board's bending stiffness. E is the modulus of elasticity, tricky to determine for composite materials (wood+fiberglass), but you can use it as a rough guide for selecting a softer wood or even a foam. I is bending moment of inertia, you can tweak this by changing up the board's cross-sectional area. https://www.engineeringtoolbox.com/area ... _1328.html. You're kinda limited here though by things like insert thickness and the size of your niece's feet.
So the goal would be to modify E and I such that the product of the two is 1/3 that of your adult board of reference. It can be achieved by a smaller cross section, softer wood, and a lighter weight, biaxial glass.
Check out Divide Rides journal, in the last few pages he goes through the build of his kids board, has the whole layup in there I think.
thank you guys for the inputs. I'm rather fit with the nerdy stuff and i ran some numbers and with the 1/3 stiffness approach and a light-ish glass layup and a Bcore balsa core that i use in my skis i still get a reasonable core thickness. otherwise i would increase the core thickness locally in the binding area. I used to do this on my super flexy carbon kiteboards.
My fear by using a pure biax layup is that it will be too stiff torsionally. i would like to keep it rather soft in torsion to get easier rider inputs.
Divide has the layup specified but not the core thickness.
In snowboards a biax layup usually refers to 0/90° fibers and not +45/-45°. That way you get a board that has some stiffness mainly along its length but is torsonally soft.
Aha thanks chrismp for the clarification. this is what i had in mind actually using a unbalanced fabric with more fibers running in 0°
flex.PNG (27.9 KiB) Viewed 2540 times
this where i'm at right now. I'll keep you guys posted on the progress.
I've done a couple of boards with 450gsm fibre top and bottom, 0' / 90'. 6.7mm core and they were really quite soft, even with some carbon fibre added.
You could grab a bit of 5mm wood that is about 230mm wide and press it with glass and Ptex and see how flexy it is. Even a 900mm length will give you the info you need.
I’ve built kids boards. Get some lightweight 0/90 glass and some light wood with some flex. You need to keep the core thick enough to hold the inserts. 5mm is the smallest insert I had. Put a decent sidecut in it. 6 meter
I used 18oz. Sound heavy but it worked
SleepingAwake, I'd be interested to poke around in that spreadsheet of yours if you wouldn't mind sharing.
I would love to share the spreadsheet, but cannot because it is an adapted work thing. But it is just based on sandwich theory and basic mechanics and for sandwich panels we get within 1 to 2 percent of the calculated stiffness.
Alright making some progress here. Balsa core with some weird wood at the inserts, bamboo sidewalls with cast tip and tail spacers. core thickness would be 5.6mm, so i'm going to locally increase the core thickness in the insert area to accommodate the 6mm inserts.
Why you dont make the inserts shorter?
Why you dont make the inserts shorter? And .... 0.6mm more length for the inserts will be absorbed by your fibres (depending on the fibre weight)
Lookin good! I'm curious to see how balsa works out for ya.
> mammuth wrote: ↑Thu Oct 17, 2019 12:07 am
Why you dont make the inserts shorter? And .... 0.6mm more length for the inserts will be absorbed by your fibres (depending on the fibre weight)
The inserts come with a cap which is handy, the small step in the thickness will not increase the overall flex anyway as this area is much stiffer with the bindings anyway and i much rather keep as much thread as possible. And the fiberglass isn't much thicker than 0.4mm (not 0.6) so for sure will not absorb the thickness without a bump in the topsheet.
> leahicmoradnuf wrote: ↑Fri Oct 18, 2019 10:37 am
Lookin good! I'm curious to see how balsa works out for ya.
I built plenty of skis with those cores so can't see a reason why it wouldn't work!
Super stoked with how it turned out! Flex is still on the stiff side i feel tho. I'll let you guys know the layup and core profile when I'm not on mobile. I used the printed fabric from freaks of fashion and the colors turned out awesome! I pre-laminate the top laminate tho in vacuum infusion so no experience how it is to work with with a wet layup.
Nice work! I love the graphics!
That's awesome ! Great job !
> chrismp wrote: ↑Tue Dec 31, 2019 9:07 am
Nice work! I love the graphics!
yeah I too love the graphics, btu cannot take credit for those. My brother designed it based on a drawing of my godchild.
attached is the core profile. sorry for the stupid format, couldn't find a way to have a table in here.
the layup is the following:
topsheet
163gsm glass +/-45°
425gsm UD weave glass (89% @ 0°, 11% @ 90°)
balsa core from Bcomp, bamboo sidewalls
425gsm UD weave glass (89% @ 0°, 11% @ 90°)
163gsm glass +/-45°
base
Aw man! for some reason i can't see the pictures!
Wow, that board is really really cute! Cant wait till my dauthers are old enough to sensibly build Skis or Boards for them
