Lathe chuck wrenches/keys aren't too difficult to make on a lathe, Dan.
You'll need an endmill (placed in the lathe chuck.. I know, not a good
practice) or collet, and a holder of some type for the round stock that the
wrench is to be made from.
Milling on a lathe is an old and very good method of utilizing a lathe's
How the section of round bar stock is held for cutting, depends upon what
type of toolholder the lathe is equipped with.
When I made my first lathe chuck wrench, the lathe had a turret style
toolholder, which would've been sufficient, although a bit crude, for
holding the section of round bar stock.
A lathe chuck wrench doesn't need to be any particularly hard piece of
steel.. mild steel of the HRS/CRS varieties will last a very long time for a
home shop lathe.
Case hardening the square end is optional.
I had already made a boring bar holder with the lathe and a drill press, a
tap and hacksaw for cutting the slit, so I was able to use the boring bar
holder to securely hold the section of round stock for milling on the lathe.
If the existing lathe toolholder isn't suitable for holding the round bar
stock or a boring bar holder, maybe an angle plate (possibly even a heavy
duty piece of angle) could be mounted to the lathe's cross slide to
improvise a milling fixture.
A boring bar holder is a good project for a lathe owner, as one will be very
handy in future lathe usage.
If a method of holding the round stock can be realized, then cutting/making
the square end (or hex, etc) can be achieved by utilizing a square to check
the rotational positioning of the round stock after each flat face has been
As the workpiece is held perpendicular to the spindle axis, the end of an
endmill (hopefully larger in diameter than the width of the flats need to
be) is used to cut away the diameter of the workpiece with cross feeding
cuts, until the correct size of the square dimension is reached.
Using a square to check for squareness by referencing it to the lathe chuck
face or a flat horizontal surface of the lathe will ensure that the square
end turns out to be square.
A round file is handy for blending the faces of the flats into the diameter
of the chuck wrench body/stem. This step can be accomplished with the lathe
spindle stopped, or with the workpiece in a bench vise.
The T-handle can be another smaller section of round stock (with carefully
radiused ends, of course). The handle an be welded to the top of the chuck
wrench body/stem, or thru a drilled hole near the top of the body/stem.
A press fit an be easily used (particularly if the T-handle section has been
prepared with a larger section in the center, or a knurl, or staked with a
punch/chisel), or held securely by a set screw that enters the top of the
wrench stem in a centered hole that is cross-drilled to meet the T-handle
The holes for the T-handle and the set screw can be performed on the lathe
if a drill press isn't available.
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