I'm jumping into the middle of this so I'm responding to one of the original posts. If the shaft is breaking above the hosel, it's not the epoxy. If the epoxy bond were failing you would see a spiral failure down into the hosel, or the head would simply come off. I think Dave T is on the right track. Manufacuturer's reinforce the shaft tips to help distribute the shear, bending, and torsional stresses onto the shaft. It helps the tip deal with stress concentrations. Two possibilities come to mind. The first: if the shaft is being tip trimmed to help 'stiffen' it up, there may not be enough reinforcing left to protect the tip. The second possibility is similar: if the bore in the hosel has been bored deeper to provide more epoxy bonding area, or it is a bore through head and the shaft was designed for a standard hosel bore depth there may not be enough stiffening left above the hosel to protect the tip.
Dave is also right about the torsional stiffness of the shaft having little to do with this. The difference in the amount of twisting that occurs in the short length of shaft engaged in the hosel between two shafts whose stiffness are less than a factor of two apart is minuscule. Unless there is a difference in the design of the two shafts that would cause the stiffer shaft to be weaker (which is counter-intuitive) it is unlikely to have anything to do with the torsional stiffness of the shafts.
My vote is that something is being done to reduce the tip stiffening the manufacturer designed into the shaft. If this is indeed not the case you may simply be exceeding the design margins the manufacturer put into the shaft.
Also, if the shafts are breaking off reasonably straight across, it is likely that it is the toe-down bending caused by the centrifugal forces on the club head at these high swing speeds that is breaking the shaft, and this is definitely a tip reinforcing problem (bending stresses are greatest just above the hosel and decrease as you move away).
Good luck,
Alan Brooks
At 09:34 AM 7/25/03 -0400, you wrote:
All of the drivers that this guy breaks, break flush to 1/4" above the top of the hosel. The reason why I'm asking is because I didn't make the club but do want to help this guy from breaking so many shafts. He has a swing speed of 152 mph and has to carry a persimmon, steel shafted drive in his bag incase he breaks both long drivers he has in the bag. I would assume he's SOL until he finds a shaft with enough torque to keep the shaft from breaking, but not too much torque where it effects his ball flight. The guy that did assemble the driver had left about 1/8" of paint on the shaft going into the hosel. Could that be the problem?
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