One of the more awkward jobs to do accurately is marking the exact point over which a plumb bob hangs. Using the actual tip of the bob can damage it, especially if marking concrete, and is just, well, brutish.
One approach I've seen to this problem is a bob shaped like a horizontal washer with four arrow points that point inward to the center of the annulus. After the bob comes to rest it's lowered carefully onto the stuff to be marked and a pencil mark made at the center of the four points. While it might work, it seems a bit gimmicky plus it wouldn't work well if the surface to be marked is angled.
IMO, a much better solution would be a plumb bob with interchangeable points. Unscrew the normal, sharp steel point and fit a thin, ultra fine point Sharpie. Then simply lowering the stabilized bob onto the surface would leave a precise mark.
Maybe I'm overthinking things - a machinist designing a push broom. Perhaps nobody needs to mark the sub-bob point that accurately.
Last edited by mklotz; 11-13-2018 at 12:55 PM.
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