The Gearbox Case / Cover III

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

  With the cover CA'd to the case, the assembly is chucked and clocked using the case body to ensure 0 runout. Do not skip this step. Taking light cuts, the cover is faced to the correct 5mm thickness. Next, a scrap of aluminum was center-drilled and used with a live center as a pressure pad to keep the cover in place for the susequent turning. Avoid any damage to the cover's bearing hole by using a scrap of sufficient diameter.
  The OD of the cover is turned to match the case. In my situation, since I plan on foregoing the cowl, I turned the cover to the major OD of the case for a seamless unit. Next, a tool of appropriate radius is used to shape the outer portion of the cover.
The almost-finished assembly, with the cover still held in place with the drops of CA glue.
For the many holes in the cover and case, I turned to my vertical mill. Equipped with a DRO, I am able to use a simple program which generates X,Y coordinates for the holes in question. The case is chucked in a 3-jaw lathe chuck clamped to the mill table. If you use this method, remember that the intermediate shaft holes will be bored through the entire assembly, so position the case in such a manner as to preclude boring into a chuck jaw.

Perfect centering under the quill is done with a centering indicator, shown here. These amazing tools cost less than $100 U.S. and are capable of repeatable centering to probably less than .0002" / .005mm of truth; an excellent addition to the shop.

First, the outer bolt circle is drilled, remembering that the drill for the cover is a through-hole, while the holes in the case will be tapped. The plans call for M2.5 fasteners, which I am changing to Imperial 3-48, a perfect match.
With some aggressive boring to come, I elected to tap 4 of the holes to really keep the cover in place.
Shown here, the 4 holes were tapped and 4 ea. 3-48 SHCS used to secure the cover.

Next will be the boring of the intermediate shaft holes. The front hole will be for a ball bearing. the rear hole will be a press-fit of the intermediate shaft spigot.

Gear Case / Cover Part 4 | TurboProp | Home