Just completed the fourth variant. Will be going to test all four soon.

This one has a old tripod head installed on a 1/2-13 threaded rod. There is a snug hole in bar, the two knurled nuts will allow vertical adjustment. The bar will be clamped to front edge of bench. Should be close enough to the bench to allow adjustments during a hot range.

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[Linked Image from imagizer.imageshack.com]