Flex Considerations

Post by **Silber** » Wednesday 1 August 2007, 17:37

Just would like to post something Bruce Varsava (Coiler) wrote in a thread on BBonline on the topic of Flex. Found it very interesting..(Hope Bruce won't mind it)

Please let me speak on the subject as I have spent a bit of time on it As you may know I do put a stiffness indication # on the side of every board. It is just a static measurement that gets the board in the ballpark for its designed user. However, being ballpark, it is still miles better than having nothing at all. Even for different flex patterns the numbers are somewhat similar as if the overall stiffness is right, the flex pattern will change the performance a bit to get the desired ride but the overall stiffness of the board is close to the same. Of course if you get into some real off the wall patterns, that is a different story. As builders what we are up against is the actual tolerances of the core thickness, which we can control if careful but the real demon is wood density variables. Even using the same species in an identical configuration can give drastically different results in overall stiffness. This is especially a factor in cores that use strips in the 3/4"ish wide configuration. Cores with narrower strips will naturally have a more consistent stiffness due to the law of averaging out. Even using wood from the same planks will have differences due to grain directions so its impossible to get the same thing every time. I once did 2 identical boards with cores accurate to 1/10mm and the stiffness came out to approx 50lbs of rider weight difference. One core was real stiff, the other quite a bit softer and that was all it took. Since my cores are cambered it may well affect my process more than others.
The metal boards are certainly interesting in that you can get by with a way softer board and still get massive edge hold from it so the results are a bit deceiving. I find that you can ride the softer boards but there are limitations especially in softer snow of course. They work like no others on steep icy hills though! For some reason they tend to fold less than a softer glass board also. Can't really say why but I feel its due to the different kind of flex the metal offers throughout the various sections of the board.
Never did get around to doing a torsional stiffness measuring system as it is a tough thing to figure out and just from experience I know approx the amount of materials to use to get the desired results per application and that seems to be good enough. Some of my glass race boards have a varying torsional rate throughout the length so it would be really tough to measure those.
So if you are thinking a measuring system would be good, you are probably right. If you are thinking you are going to see one widely accepted, I doubt it. Most boards come out different ( even identical models) as it is real hard to get them exact with all the variables in play. Good old fashioned labor and extra time during the process can remove a lot of the factors and that is the way I get around it. Probably takes me 2 hrs or so per board just dealing with those factors. Pain in the ass but the end results are worth it.
Cheers, BV