After first attempting to use a conventional drill press vise to hold the walnut eyepiece housings while I bored them, I eventually made a very simple jig. This proved much easier to use and cost me nothing, because it uses scrap material I already had on hand.

	The jig is comprised of two pieces of wood screwed together at a 90° angle. Holes were drilled through the wood at various locations for bolts that attach the jig to the drill press table.
	The jig is secured to the drill press table with ½-inch bolts, lock washers, flat washers, and wing nuts. The wing nuts allow easy adjustment of the position of the jig. The diameter of the bolts was determined by the width of the slots in the drill press table.
	A scrap piece of ¾-inch plywood is placed on the drill press table. Otherwise the drill bit will strike the table when you bore through the eyepiece housing. The eyepiece housing is placed in the corner where the two pieces of wood meet.
	The eyepiece housing is held securely in the jig with a large C-clamp. A small scrap of wood is placed between the clamp and the housing so the clamp will not mar the housing.
	In this closeup, note that the back corner of the jig has been flattened to give the C-clamp a flat surface to bear against. Note also the centering marks on the surface of the eyepiece housing. The jig and drill press table are moved as required to center the housing directly under the point of the drill bit, then the wing nuts are tightened to hold it in place.