Craig,
If you really want to find the spine on any thing, and or any length - you can use rod rests to do a precise job.
Here is a picture of some of the very first rod rests that I made a very long time ago, but the fit and function still work very well today:
[
www.rodbuilding.org]
To check for the spine of a blank of any length, simply take 3 of the rod rests pictures above and remove the bar with the single bearing on it from the rod rest. Then, take one of the three rod rests and turn the remaining bar with the two ball bearings on it - upside down.
When using these rod rests, I have a board with a slot in it that will accomodate a 1/4 inch carriage bolt with the head of the bolt on the underside of the board with the head of the bolt resting in a widened slot on the underside of the board to allow the bolt to slide up and down the board without touching the rod bench.
Now, to use the setup, take the two rod rests with the double rollers and set the rollers at an equal convenient height. Bolt them down so that they are 2-3 feet apart.
Then, take the 3rd rest with the double rollers facing down and bolt it 1/2 way between the two other rod rests.
To use the spine finder just made, simply lift the roller bar out of the way on the middle rod rest and lay the rod blank on the rollers of the two outside rod rests. Place the rod blank in a part of the blank that you would like to check for the presence of a blank spine.
Then, place the bar with the rollers on the underside of the bar, back on the rod uprights and press down, until there is a significant bend in the rod blank. Tighten the thumb screws.
Now, simply rotate the blank a few times checking to see if it stops in the same spot evry time. iIf it does stop in the same spot every time you have found the spine, so take a pice of thin (like 1/8th inch wide painters striping tape to mark that side of the blank to mark the spine.
Then, repeat the same thing several inches or even a foot or more in a couple of different spots on the blank to see if the spine changes as one goes up and down the blank. Don't be surprised if you do find a change. But go with the spine that you find that is most pronounced.
Then, repeat for other blanks or other blank sections.
Once the rod rests or spine finder is setup, you can find the spine on a blank in a few seconds - mark the blank and then move on to the next one.
If one is serious about using the spine - you can have the spine finder setup, any time that a new shipment of blanks or blank pieces arrive. Then, just go ahead and go through the entire shipment of blanks - placing a piece of tape on the blank - marking the spine.
---------------------
But, as ai said earlier, I personally disregard eny part of spine, and or spine finding on a rod blank when building a new rod. Rather, i simply build on the side of the blank that is most straight.
