More on Spines
NOTE 15: A spine tester will indicate the weakest axis of the shaft. No shaft can be perfectly uniform therefore there must be a weak axis somewhere. Most clubmakers believe this axis should be pointed either directly at your intended target or directly away from it. There seems to be no consensus whether one direction is better than the other. Pointing the spine axis in the plane just described makes a lot of sense to me. In a spine tester when the shaft is bent it will attempt to rotate such that it is being bent in its weakest direction. During the swing, the club for the most part bends in the direction of the swing plane. If the weak axis is lying in this plane there will be little tendency for the shaft to rotate during your swing as it does in a spine finder. I don't know how strong this rotational tendency is but why not minimize it?
If your interested in a spine checker one can be obtained from Colin Dick. I don't have his address but his email is . I believe they're about $35. If you own a Club Scout and want to experiment, the clamping unit can be used as a spine checker if you simply purchase three ball bearings. Get two bearings with a 5/8" ID and an OD of less than 1 ¼" and a third bearing that will fit over the tip of the shaft. Place the two bearings at either end of the lower V block in the Club Scout clamping unit. Place the upper V block on top of the bearings and tighten the torque screw to securely hold them in place. A shaft can now be slid through the two bearings. The third smaller bearing is now placed over the tip of the shaft. (The Club Scout split bearing clamp accessory works great if you've already obtained this accessory). As the shaft is bent it will rotate to its weakest axis because of the freedom provided by the three bearings. Sometimes you have to twist the shaft a bit to get it to rotate.
Added Note: When I wrote this some time ago I thought of the spine
as the weakest axis of the shaft since that's the orientation the shaft
naturally rotated to in a spine finder. Although it's still a bit fuzzy
most people now a days think of spine as the strong axis. I hope this
doesn't muddy things up too much.