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.

  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.
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.
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.
This allows chucking of the square stock!
After turning and parting, I ended up with this handful of banjo bodies, as yet undrilled for the perpendicular port.

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.

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