John R. Bentley 2007.
Naphtha Launch Propeller
Steep pitch and "square" tips!
This prop is 3 1/4 inches in diameter and has a pitch of 14 inches at 0.75% diameter
Okay - of course the tips are not actually square but appear so if compared to many modern props. Actually this vintage style is similar in this respect to modern Kaplan propellers but without the shroud (Kort Nozzle). The tips are arcs of the circumference of the circle which they describe when the prop is turning. Therefore if looking at the shaft end-on in a 2-dimensional view each blade appears as a sector of the circle.
Milling 1/16" slots in the hub for the blades
(I mounted the vise at an angle on the mill table then just cranked the x-axis handle)
Hub screwed on to the shaft
Embryo blades and the threaded hub
A test fit, prior to silver brazing
Still cooling down after being at dull red heat!
Bending the blades in the vise
to reduce the pitch as the diameter increases
Ready to trim the blades and hub in the Craftex lathe
This job could have easily been done in the Taig lathe, but I used the Craftex 7" x 8"
An eagle eye might notice a Taig live center being used here in the Craftex lathe
- it was held in a 1/2" capacity tailstock drill chuck
A flat needle file ready to go to work on the blade camber
Entry sides are done - now to the flat back sides...
Darn near done!
(I did round just the corners of the tips slightly more when finished)
Milling 1/16" slots in the hub for the blades
(I mounted the vise at an angle on the mill table then just cranked the x-axis handle)
Hub screwed on to the shaft
Embryo blades and the threaded hub
A test fit, prior to silver brazing
Still cooling down after being at dull red heat!
Bending the blades in the vise
to reduce the pitch as the diameter increases
Ready to trim the blades and hub in the Craftex lathe
This job could have easily been done in the Taig lathe, but I used the Craftex 7" x 8"
An eagle eye might notice a Taig live center being used here in the Craftex lathe
- it was held in a 1/2" capacity tailstock drill chuck
A flat needle file ready to go to work on the blade camber
Entry sides are done - now to the flat back sides...
Darn near done!
(I did round just the corners of the tips slightly more when finished)
The propeller hub is threaded through. A 3/16" shaft is threaded at the outboard end. A nut on the protruding thread locks the prop on the shaft and a second thinner nut acts as a locknut. The shaft end is pierced to take a split cotter pin.