The Gearbox Case / Cover IV


Work continues on the gear case and cover, being built as a unit to ensure excellent alignment.

  After tapping 4 "corner" holes, the cover is well secured, and the gear case once again centered dead true in the vertical mill. The remaining axial holes are located and drilled. These include the drain hole South of the central bearing, and 8 holes to secure the prop shaft tunnel.
The mill table is moved the correct distance for the boring of the intermediate gear shaft holes. The hole in the front cover is a boring for a nice hand-press fit of a bearing, and the hole in line with this, in the back of the case, is a hole for the intermediate shaft spigot. The plans called for a metric hole which I altered to a 1/4" hole, as my drills and reamers are imperial.

Here, the bearing hole is bored with a precision boring head. Use care towards the end of the boring to get it "just right", otherwise, a lot of work would be wasted.

A check of the hole shows a correct dimension has been bored. Now, without moving the table at all, we change the mill tooling in preparation to drill and ream the rear of the case for the intermediate shaft spigot.
Boring this hole would be best, but it is practical to drill and ream if the hole is first drilled or spotted with either a stiff and extra-long centre drill, or in this case, a carbide drill of this flute style, sometimes called a spotting drill. This is the exact carbide drill I used to drill and ream my MW54 thrust turbine wheel, and measures 15/64" or .234".
The carbide drill is exceptionally stiff and will not wander at all. The hole is drilled, and then reamed to 1/4" with a spiral fluted reamer. The spigot must be modified to fit this slightly larger hole.
Finally free of the setup, the gear case and cover is cleaned up, deburred, and generally coddled! All that remains is to tap the remaining holes where appropriate.

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