This is probably old hat for many of you, but I needed a way to index round parts at 60*, 90*, and 120* for drilling and milling.... I purchased a set of 5C Collets and a pair of holders for them, a Hex and a Square....



The square holder worked fine in the milling vise on my Atlas lathe, but the hex wouldn't quite go deep enough to secure properly.... I measured the difference in width between the square and across the points on the hex, divided by two, and milled a 1/2" wide slot to that depth (0.130") at the appropriate height across my vice....



While I was at it, I milled flats on both sides of the vice and drilled and tapped 10-32 holes so that I could put a stop on either side of the vice.... Now I can use the square or hex mounts with collet in the vice, rotate them to index the part, and the stop will set the holder in the same place each time....



I'm looking forward to trying this arrangement out the next time I make an airgun valve or drill a tube to accept it....

Bob