Flat Line Oscillation (FLO) vs Center of Gravity
TECH NOTE 29: In the spine alignment process we try to determine the two planes in a shaft that produce flat line oscillation, i.e. no wobble. This is very often done with a tip weight rather than the actual clubhead. The questions arises," will the FLO change when I install the head because its center of gravity is offset from the centerline of the shaft?" Golfsmith claims it will not change. I was curious. If a change in FLO does occur is it due to the change in cg or because it's hard to twang the club straight up and down when your finger is twanging somewhere out on the clubhead rather than on the centerline of the shaft?
To test this I built a tip weight with an arm sticking out of the side of the piece that attaches to the shaft. This piece weighed about 100 grams. I placed another weight on this arm and held it in place with a setscrew. This second weight also weighs about 100 grams. This arrangement allowed me to vary the cg of the test weight by more than an inch in a direction at right angles to the shaft. I attached a very small key chain laser to the tip weight. I built a trigger release system to eliminate any variations due to finger plucking. I placed a 10" disc on the butt end of the shaft. With degree lines on this disc it was easy to repeat alignments as I searched for the FLO. I determined the FLO plane as accurately as I could with the laser projected about 20 feet across the room. I then adjusted the side weight to move the cg about an inch. I did not find any variation in the FLO plane. I guess Golfsmith was right.
Another winter project is to measure the FLO with a tip weight and then with an actual club head to see if there is any difference as people have reported. I'd then like to build a little trigger that would allow me to twang the shaft with the club head attached but never actually put a finger on the club head itself. I figure some little collar around the shaft near the hosel should work.
There seems to be some fetish about determining the FLO within a degree or so. This struck me as a bit of overkill. While I was running these tests I moved off of the FLO plane by about 5°. When I twanged the shaft I had very flat line oscillation for at least five oscillations of the shaft before a wobble started to develop. Since the shaft on goes through a single cycle (or less) during the swing is it important to worry about what happens after the fifth cycle? In my opinion it's not critical to find FLO down to the Nth degree.