Prop Shaft Housing Part II


Part 158, the prop-shaft housing, is machined from another chunk of wrought aluminum alloy.

  The prop shaft housing is secured in a 3-jaw chuck clamped to the mill table. Coordinate holes are derived for both the nose and the base of the housing.
I drilled my nose pattern sized to tap 3-48, a close match to M2.5. The base circle is drilled clear 4-40 to match exactly the pattern in the gear case cover. Again, use of coordinate drilling and a DRO allows me to drill matching bolt-circle patterns separately with success assured. Without a DRO, it is best to drill these parts mated, as illustrated by Mike in the operations sheets.

Since the base circle is tightly spaced relative to the nose, the drill chuck would interfere when using normal center-drills to start the holes. To remedy, I used an extra-long center drill to spot the holes first, followed with the correctly-sized drill.

Two more important operations remain... First, the intermediate shaft front bearing inner race must be cleared from the front cover by machining or drilling said clearance in the cover at the correct location. Secondly, the drain hole must be continued from the front cover and into the tunnel itself to drain any oil pressed forward by the pumping action of the spur gears.

To ensure alignment, the prop shaft housing and the gear case cover must be secured together properly. The best way to do this is to insert a bearing into the housing; then, the cover is lowered, allowing the bearing to register both parts.

With the housing and cover together, 4 of the cap screws are used to secure.
Back in the mill, the intermediate bearing bore hole is located by any standard means, and a center-cutting end mill may be used to good effect. For me, a 2-flute, 1/2" / 12.7mm end mill is perfect. The relief need not be deep, perhaps .032" / 0.8mm.

While in this setup, the drain hole may also be located and drilled through to the tunnel, per the print.

The prop shaft housing, gear cover, and case together on the bench. Note that I still haven't turned the undercut in the nose.

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