- Joined
- Jan 12, 2017
- Messages
- 570
On the Wooden Airplane forum I started a thread about a year ago describing my efforts to carve a wood prop for my Flitzer Goblin project and asking about the best wood to use.
I'm now at the point of wanting to drill the bolt holes. The prop does not fit on my drill press table. After a couple of attempts to fabricate a prop hub drill jig sufficiently true to allow hand drilling of holes that match both the mounting plate on one side and the pressure plate on the other (my prop hub is 3 7/8" thick), I came up with this design, FWIW.
The bushings are 1/2" x .095 wall for the 5/16" bolts (reamed to finished ID) and thinner wall for the 3/8" center hole (also reamed a bit). The plates are 1/8" mild steel.
Once the 6 hole, 4" BCD pattern was cut (using a 1/2" Rotabroach) in each plate (ignore the empty set of holes in the top plate, which were not quite right), I aligned the two plates using two small machinist's V-blocks holding the center and one of the perimeter bushings. With the assembly clamped together, these blocks ensure the bushings are perfectly vertical and the plates are perfectly horizontal. To avoid undue distortion from welding, I only tack welded the bushings to the plates: on top of the top plate (which does not need to be smooth) and on top of the bottom plate (which must be smooth below for clamping later to the prop hub).
I have not yet drilled my prop, but I have tested the jig on a thick wood block, and the results were excellent.
I'm now at the point of wanting to drill the bolt holes. The prop does not fit on my drill press table. After a couple of attempts to fabricate a prop hub drill jig sufficiently true to allow hand drilling of holes that match both the mounting plate on one side and the pressure plate on the other (my prop hub is 3 7/8" thick), I came up with this design, FWIW.
The bushings are 1/2" x .095 wall for the 5/16" bolts (reamed to finished ID) and thinner wall for the 3/8" center hole (also reamed a bit). The plates are 1/8" mild steel.
Once the 6 hole, 4" BCD pattern was cut (using a 1/2" Rotabroach) in each plate (ignore the empty set of holes in the top plate, which were not quite right), I aligned the two plates using two small machinist's V-blocks holding the center and one of the perimeter bushings. With the assembly clamped together, these blocks ensure the bushings are perfectly vertical and the plates are perfectly horizontal. To avoid undue distortion from welding, I only tack welded the bushings to the plates: on top of the top plate (which does not need to be smooth) and on top of the bottom plate (which must be smooth below for clamping later to the prop hub).
I have not yet drilled my prop, but I have tested the jig on a thick wood block, and the results were excellent.
