Because the drill press obtained for the workshop turned out to be unsuitable for milling.
The chuck was installed with a Morse taper
#2, and had no other mean for retaining the
taper than mechanical friction - which is all okay as long as there is axial pressure holding
it in. Which is what happens during drilling - but not during milling, where the forces are
primarily lateral. The taper kept dropping out. A way to hold it in was necessary; a collet
with holding screws was therefore designed and made.
As the initial piece of material a steel M18 nut was chosen, for its
suitable internal diameter that promised enough space for both the drill's own taper holder
and the chuck's taper.
The faces of the nut were machined to be more flat. (Not entirely necessary but good for warming up the lathe operator.) The central hole was machined through to inner diameter matching the Morse taper shaft. Then the hole was widened into half the nut's depth to match the drill's taper holder diameter.
Six holes were drilled into the nut, in sets of three and three, for the mounting screws to affix the collet to the drill and taper. M4 threads were cut, one with a machine tap, five more with a manual tap (as the operator made a mistake and broke the machine tap. Ka-ching, says the tool vendor.) The burrs were abraded away with a small spherical sand wheel.
The collet was affixed to the drill and taper with six M4 hex-key screws. (One of the screws got its head torn off due to overtightening, presenting a problem for the future when the collet will have to be removed.)
Initial tests suggest the soundness of the approach. The drill is now capable of serving as a mill.
 Source nut, bearing holder (another project), drill press collet |  Drill press collet |  Drill press collet |  Drill press collet |
 Drill press collet |  Collet and chuck with Morse taper #2 |  Drill press, no chuck installed |  Drill press, collet in place, no chuck |
 Drill press, no collet |  Drill press, no collet |  Drill press, Morse taper pulled out |  Drill press, Morse taper end, detail |
 Collet in place |  Collet in place |  Collet in place |  Collet in place |