The Gearbox Case / Cover II


With the gear case behind us, work proceeds on the case cover, a relatively thin disk of aluminum. I liked Mike's suggestion of using CA glue, and as you will see, proceeded along those lines with some minor procedural changes to fit my equipment and inclination.

  A blank disk of aluminum, oversized in diameter and thickness, was chucked. The first step was to create an accurate face, and then cut the register rim which is fitted snugly into the gear case. First, the disk was accurately faced.
  I then carefully approached the correct diameter of the register, using the case itself as a guage to test the fit. Use care; we want the cover to snugly fit into the gear case with no appreciable play.
Success! The gear case is a nice fit, and easily able to remain on the disk blank without support. This helps ensure alignment of the bearings when the case is finally assembled.
Since the register is a simple 1mm rim, I then had to profile the rim from the inside as well. A 1/2" hole was drilled through the disk to start my boring tool, seen here making the appropriate cut.
The rim is complete. The ID of the rim is not critical but shoot for a 1mm thick register as per the print.
The next step is to create a precision bore for the bearings which support the rear of the prop shaft. These too need to be a close sliding fit, with 0 play in the bearing itself.

As we approach the correct size for the bearing OD, use accurate bore guages and a good micrometer to measure the bore. When the bore is within .0004" or 0.01mm, the use of 600 grit paper, seen here, is helpful. Trying to take a .0004" cut with a boring tool is asking for trouble, as it is easy to cut the bore oversized. Go slowly, and finish out the bore with 600 or finer paper for those last few "tenths" of a thou.
The test bearing is now a perfect, close sliding fit.
The disk is reversed, and excess thickness of the cover, as much as can be allowed with the chuck and the tool, is removed with multiple passes of a facing tool.
Note that the outer face cut in the previous picture need not be perfectly parallel, as we will finish the cover in situ, attached to the gear case. In a nutshell, the portion of the cover which mates with the gear case is finished to perfection; then, the outer portion will be finished later, where correct dimensions and parallelism can be obtained due to its mounting on the case.

Shown here is the oversized cover CA'd to the gear case.

Gear Case / Cover Part 3 | TurboProp | Home