With lighter powered bare blanks that will oscillate for a while when the tip is struck when the butt of the blank is taped to a table, I notice that there are some axis where the blank will quickly oscillate into an oval shaped movement. At other axis, it will oscillate in a straight up and down direction.

What are the factors that causes the oval oscillation?
Is this relevant to building? (When buidling super lightly where the guides and finish contributes very little to the final weight, my guess is that it does somehow - but how?)

I figure if ANY forum on the planet will know, it's this one....:)

Thanks,
Mo

ps: I've search the forum for oscillation and came up with one post. Perhaps I did an adequate search?

Ah - the Emory Harry boing test. I have found the same thing once but only on one blank. It had the famous double spine - but one blank is not enough to based anything on. Especially since the spine is "an effect and not a thing" - or is it two affects and not two things?

Clamping a rod blank to a table and then striking the tip doesn't approximate anything that will ever take place out on the the water. No blank will ever oscillate like that in actual use - the butt is held by the human hand (not clamped to a fixed object) and in a state where that sort of thing just isn't going to take place. So no, it's not really relevant, at least not any more so than using a spine finder or any other method to find the spine.

Guys who do this, and it's an older method for finding the spine, will tell you that such an oval oscillation pattern means your strike or blank orientation is out of line with the spine effect. So the natural movement you've created is being affected by the spine and then results in something other than a perfectly straight up and down motion. A slight oval motion even. When you have the spine straight up and down, the motion should follow that direction.

Where the blank flexes and primarily oscillates from can also cause an oval pattern such as you describe. If the blank's motion is coming mostly from a distance beyond the tip, and the blank isn't perfectly straight (few are) then even if it's moving straight up and down, an off center tip is going to travel in an what appears to the eye as an oval.

If you build the rod with guides and finish, on any axis, and repeat the test, you'll likely find that the rod tends to oscillate straight up and down no matter where the spine is - You've added more mass to the rod and once set in motion, it will continue to move in that same direction until something changes it. The more mass you set in motion, the greater the force required to change its direction will be. And this will hold true even if you have the spine oriented well away from an up and down orientation.


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