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With as much turning and boring accomplished as
possible, the shaft housing is parted, with plenty of
stock remaining on the gear case flange for cleanup and
facing to length. |
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The current shape of the housing is awkward and
cannot really be held directly in a lathe chuck. For
subsequent holding, an expanding mandrel is turned to
exactly 14mm, the inner bore of the housing. A regular
mandrel can be used but it is a lot more work and must be
made precisely, whereas an expanding mandrel will grip
tightly and need not be turned to perfection. Be sure to
smooth the mandrel, deburr, and clean it generally, as we
do not want to harm the housing bore. The housing is
mounted with the gear case flange out, and checked for
eccentricity. Correct if necessary for 0 TIR for boring
of the bearing seat. With that accomplished, the housing
is also faced to the correct length on the lathe.
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For the 2 bolt circles, the mandrel is moved to the
vertical mill and centered. Here is why I made my gear
case flange a bit larger than print... it allows me to
drill all of the holes in one setup, assuring
perfect angular relationship between the two flanges. It
is also a bit stronger. The gear case flange must be
spotted with an extra long centre drill. The spots are
then drilled out, in my case 4-40 clear. I chose to
execute 8 holes instead of 6. At the same time, the hole
for the spigot is spotted and drilled clear 10-32, which
is the thread of the spigot. The extra-wide flange also
becomes the "washer" for the spigot, and the
10-32 cap screw will help secure the flange.
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The 10-32 SHCS clearance hole is drilled for the
spigot. This cap screw is large enough to require a
spotface, as the edge of the cap screw interferes with
the turned radius. Before spot facing the spigot hole,
the remainder of the holes in the gear case flange are
drilled clear for 4-40 / 3mm SHCS. |
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The spot-facing operation is complete. |
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The finished housing, nice and bright! In part 3, we
mate the housing to the gear case. |