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What does redrilling actually do to a ski's flex?

post #1 of 3
Thread Starter 
Anyone see the photo here of the B1 broken along the plane of the two open holes? In another thread about REI and drilling mistakes, I argued that a redrilled ski just isn't the same, just like a new car that was crashed and fixed.

Realized later that the real point is, we ASSUME that some skis can be redrilled, maybe even several times if they have metal in the top, without any significant change in performance. Others (think foam) we say, "naw, it'll mess up the ski." Yet I've never seen any data on this, just shop guys I respect here and elsewhere saying so. One guy told me confidently that I could redrill Stocklis half a dozen times with no effect. Hmmm.

On the other hand, we also argue endlessly over flex patterns of skis, and how much a plate or a raised binding changes same. So OK, let's say that you drill two extra holes, 8 mm each, in the same plane perpendicular to the body of a ski (we can call this a coronal plane), and let's say the ski is 80 mm across at that point. Those two holes, which extend through the topsheet and any metal down into the wood, mean that along that coronal plane, you've removed 16/80, or 20% of the width of the material down 3 or 4 cm. Then if you're careful, you stick in two plastic plugs, which are nothing like the metal or wood removed. Assuming that this removal increases flex by say half the 20%, seems to me you're in the same ballpark as what a mild plate does the other direction (increasing stiffness).

Obviously, the model is more complicated because the stiffness of the ski in that plane is not constant, but presumedly increases as we move toward the edges. Also, the footprint of the binding itself can cover the holes (or not), which may compensate (or not). And finally, a plate achieves more stiffness by covering several different planes, not just one. But IMO the basic point has to hold: drilling extra holes will reduce the stiffness of a ski, and in unpredictable ways depending on where the holes are relative to the binding, and what the ski is made of in the first place.

So why don't we notice it? Well, we may not want to hear this, but I have a hunch unless we're elite skiers, we cannot actually detect a 10% change in stiffness underfoot. I'd guess that our own COM variation and the routine oscillations from the slope are far larger.

BUT: The fact we can't tell the difference doesn't mean it isn't there, or that it won't affect handling in some conditions. Or ski lifespan.

OK, engineers, show me how I'm all wrong about this. Or better, let's see some experiments. If they can hang cans of paint off the sides of AT bindings and measure deflection, someone must want to drill up some old skis, weight the tip and tail, and see how the flex changes. Yes?
post #2 of 3
show me how I'm all wrong about this.
uh, you mean 4.5 mm each so 9/80 or 11%, no? So half (with plugs) would be 5%?
post #3 of 3


Drilling for binding mount , then plugging the holes does just about nothing to the overall flex of a ski.
Some "lightening" or lightning;-) holes are just insignificant.
Simplifed math just does not hold for composite structures.
A "plug" may actually increase compressive strength!

Don't let moisture in an unused hole that would allow delamination!

"Worry is interest paid on Trouble you do not have!"

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EpicSki › The Barking Bear Forums › On the Snow (Skiing Forums) › Ski Gear Discussion › What does redrilling actually do to a ski's flex?