How does a person go about building a "shaft straightness gauge"? I have some Mitutoyo digital dial indicators (0.0005 inch resolution X 0.500 inch travel). They were throwing these obsolete gauges out at work, and they came my way after I asked the supervisor for them.
The one I built for Charlie was a variant of things I've seen or heard about from others on ShopTalk. On March 19, 2003, I saw posts or emails from Royce Engler, Bob Boone, and Corey Bailey that gave me the idea. Start with a spin indexer, and collets the right size to clamp a golf shaft.
But the others all used some sort of mechanical gauge to measure things. Unfortunately, dial indicators have an internal spring that introduces force deflection into the equation as well as the residual bend. Thus, it has the same weakness as bearing-based spine finders: you are measuring a combination of bend and spine. The spine finder tends to emphasize the spine, and a dial indicator with a spin indexer tends to emphasize the bend. But they both have weaknesses.
What I did was mount a precision steel rule on a mirror, and put the assembly on a mount that could be affixed at one-inch intervals along the shaft. You read the bend by rotating the spin indexer and reading the position of the edge of the shaft on the scale. Being an electrical engineer -- an OLD electrical engineer -- it just came naturally that pre-digital meters of good precision tended to have mirrored scales to prevent parallax error. That was just what the doctor ordered for this job.
With this instrument, you find the peak difference at some station along the shaft, and (because the spin indexer is calibrated) you know the orientation of the peaks. You can even find a spiral shaft (Charlie found more than I would have guessed), by noting that the peaks are in different orientations at different stations.
Hope this explains it.
Cheers! DaveT
