Turbine Shaft Housing Part II

Construction continues on the Turbine Shaft Housing.

  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.
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.

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.

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.
The spot-facing operation is complete.
The finished housing, nice and bright! In part 3, we mate the housing to the gear case.

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