The compound rest on my 11” Powermatic/Logan lathe is held in position by two set screws that bear on the center pivot post. This works fine for setting angles when close is good enough. However when more precision is necessary, it is very time consuming and frustrating to get it set correctly. Just when you get the indicator exactly where you want it, as the set screws are tightened, the angle moves.
I made an adapter that allows more easily setting of angles within a within a couple of 0.0001’s of taper per inch. The inspiration for the design comes from the base an old optical surveyors transit.
The adapter is just a piece of thin sheet metal that is installed under the compound rest. The most precise work during construction was to bore a hole to match the pivot pin on the compound, then drill an array of holes spaced at 15 degree intervals around that hole. Then drill one hole in the base of the compound to match the holes in the plate. Sketches and photos attached. Compound adjuster.pdf
The head of an 8-32 x 3/4 socket head machine screw was turned down for a tight fit in the locating holes. The base of the compound was drilled, tapped and counter drilled for the screw, so the head is flush or a little below the plate when it is installed.
In use, an indicator of choice is set-up to display the desired movement, the compound rest set screws are loosened, but left a little snug, then the adjusting screws are used to move the compound rest while watching the indicator. When the setting is correct, tighten the set screws, then check the indicator.
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