Build Your Own Spinefinder
TECH NOTE 30: A spinefinder is a pretty easy device to build but it may require tools (a metal lathe) that most shops don't have. I built a spinefinder using a couple of ball bearings with a 5/8" inside diameter and a piece of water pipe. The O.D. of the bearings was bigger than the I.D. of the pipe. I used my lathe to open up the pipe enough to press fit the bearings into the pipe. Unless you have a lathe or are lucky enough to find bearings and a tube that are exactly the right size you may be out of luck.
There is another approach that I think results in a better device but only requires a drill press to build. I built the device using a piece of angle aluminum. This allows me to easily C clamp it to a workbench. This could be built using a flat piece of material such as aluminum, steel or even hardwood. The piece could then he clamped in a vise when used. On the inside of the angle aluminum I bolted two small PVC blocks. (I like to use PVC because it's so easy to work with. In addition I'm very fortunate to live a few miles from Midland Plastics Corp. They have a retail store where they sell all their odd ball cuts-offs. It's a do-it-yourselfer's dream come true.) Obviously you could make these blocks from most any rigid material. I screwed two small bearings close to one another on each of these PVC blocks. The two bearings form a V slot that the shaft can rest in. This is hard to describe. Hopefully the picture makes it clear.
The idea of rotating the shaft while resting in the notch formed by the two bearings probably results in less friction than passing through the bore of a single bearing. All the shaft-balancing fixtures that I've seen in catalogs use the two-bearing approach.
Normally the tip end of the shaft is bent downward while being held in another bearing. I prefer a two bearing approach once again.
I might try to build one of these spinefinder gadgets with the multiple bearings that would attach directly to my Club Scout clamp. I've sketched up several approaches and it looks pretty easy. It would allow frequency and spine finding with the instrument.
There is another neat store not too far away called the American Science Center. It is a store full of surplus "stuff". The store is full of chemical, electrical, electro-mechanical, mechanical and all sorts of other surplus gizmos. They have a box full of really nice small bearings that I used for this project. I think they were less than $2 each. If you're interested I'll send you some if they haven't run out.
I'm considering attaching a couple of bearing holder to either end of my Club Scout clamp to effectively turn it into a spinefinder. I've done it on paper but haven't really tried it yet. If you'd be interested in such an accessory let me know.