This hub is hogged out of a solid six inch diameter billet
of 7075 T6 or 6061 T6. It fits a five and half inch SAE # 1 prop flange.

This could be made on a simple vertical mill. No need for a trick 3D NC
machine tool. The top is held on with
four 3/8 bolts threaded into the base.

The trick part about this otherwise ordinary variable pitch hub is the
balls that comprise the ball bearings run directly in the hard anodised
aluminum.

This is made possible by using Torlon balls from Harken off shore racing
sailboat blocks. These hard plastic balls need no lubrication and will
work soaked in salt water. They can be bought at any boat supply place.

The propellor blades with the steel collars are screwed onto the hollow
stub shafts shown and locked with small roll pins.
 
I also added a redundant steel alignment shaft. Many current
designs get along with out such an alignment shaft
as the centrifugal loads on the blades keep them aligned.

The shaft is hardened and ground for extra precision Torrington needle
bearings. The shaft is located by the blind holes in the prop
blades. See the Torrington catalog for exact dimensions.

This is sort of  a belt and suspenders approach.

BTW this is pusher or tractor CCW or CW. It all depends
on how you set up the blades. There is about 40 degrees
of pitch change possible which is way more than is normally needed.

The 1/4 28 screw is rotated by a geared down electric motor to change
pitch.

I found a part in Home Depot that can serve as a prop
blade hub. It is a stright thread 2 1/2 inch conduit coupling.
It is about two inches long threaded on the inside.
The wall thickness is about 3/16. Cost $2.
It is made from mild steel but mild steel is stronger
than the epoxy bond between steel and carbon fiber.

The area is about 16 square inches so at a bond shear strength
of 1000 psi we are looking at 16,000 pounds with out
any help from the sine wave grooves  mechanical locks.

The weight cut down with sine wave lock grooves in the outer
surface is about 9 ounces. It took me about ten or fifteen
minutes to do this on the lathe.

It could be cut down a bit more as all two inches of
the inside thread is not needed.

Since it is located near the hub the centrifugal force
due to its weight will have minimal effect on the Torlon ball
blade bearings.

With variable pitch props costing up to $10,000 it is quite
feasible to have your own made by a competent machine shop.

If someone on here with a machine shop wants to do a kit
I will help market it to this list no charge.

Paul Lamar
 
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