Michael Koblic wrote:
Looking at chucks from various sources they seem to be mounted on lathe
spindles in a variety of ways. Most of the time I can grasp what is going on
but some of the designations stumped me: What is the D 1-4, D1-6 etc.,
mount?
The D1 series use a flat and taper to align the chuck, and a set of big
notched pins and cams to pull the chuck against the flat. The cams are
called cam locks, so the whole system is often referred to as a cam-lock
chuck or spindle. The cams are radial pins with an eccentric section,
and are mounted in the spindle such that the look like an extra set of
chuck pinions. Often, the same chuck key works both. The spindle face
needs to be very accurately machined, as well as the matching chuck
backplate, as both the taper and flat are supposed to mate at the same
time. This essentially means zero tolerance on the fit.

The chuck is VERY securely mounted with this method, for instance a D1-6
can have 6 cam-lock pins, each nearly 1" in diameter, holding it on.
Generally, D1 spindles have some of the largest through holes for their
size. For instance, my Sheldon model R15-6 15" lathe with D1-6 mount
has a 2.25" spindle through hole.

Jon