Banjo Fittings
At this stage in the turboprop construction, all of the larger, more important parts are finished. All that remains is the plumbing. Normally this would be a matter of a couple hours of work, but I wanted to use metallic tubing, hence the need for some fancy fittings.
A banjo fitting is a device used to connect a line at 90 degrees to a port, and allow the connection full rotation about the axis to the port. This will be critical to keep lines neat and the fitting easy.
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On the gas gennie service port area, I had already fitted 10-32 imperial adaptors, female threaded. These were tightened more or less permanently to the face of the turbine with the rig upper right... a SHCS and nut to drive the adaptors in place. The former is easy to remove by loosening the nut. Washers were made of Rulon-J, a synthetic plastic material with enough "give" to seal, but not distort excessively. |
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The body of the banjo was made of 3/8" T6 aluminum square. A series of 1/4" holes for the stem was reamed in the mill. |
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To turn and shape the bodies, and lacking a 3/8" sq. 5C collet, I made an emergency collet from an aluminum round which I first broached 3/8", then split. |
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This allows chucking of the square stock! |
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After turning and parting, I ended up with this handful of banjo bodies, as yet undrilled for the perpendicular port. |
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The stem of the banjo is made of brass hex stock, turned 1/4", cross-drilled, relieved, and threaded. The o-ring at the top seals the stem inside the banjo body. The thread is 10-32 to match the service ports on the turbine. |