August 2019 69
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Gimmel Rings
lathe, where an 8.5mm slice was parted off.
The end was again faced before another
8.5mm slice was taken.
The next task was to face the cut sides of
each slice and reduce the thickness to 8mm.
But how to hold them?
I needed an expanding mandrel but, since
I didn’t have one, I had to compromise. I
rummaged around in the scrap box and
found a 100mm length of 1.25” bar and a
½” BSW screw.
I faced the end of the bar and cut an
8mm×28mm shoulder, then drilled a
10.75mm axial hole and used a ½” BSW
taper tap to create a threaded portion just
deep enough to accept a few full diameter
threads. I then made two longitudinal
saw cuts to create the mandrel shown in
photo 13.
The slice could then be placed against
the shoulder such that when the screw
met the shallow threaded section, further
tightening opened the saw cuts to grip the
slice fi rmly enough to allow the cut side to
be machined as in photo 14. Aft er this, the
5.3mm holes in one cheek were tapped M6,
and those in the other were opened to M6
clearance (6.1mm).
This procedure was then repeated for
the 55mm cheeks, which were made from
a portion of the 65mm bar turned down
to 55mm.
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13 14
15 16