How to Pitch the Propeller
1. Straighten any ragged areas on an anvil or steel plate. If
some pieces break off they will have to be welded after pitching.
2. Mount the correct pitch block to the base and use the
largest mandrel that will fit through the bore of the propeller.
3. Slip the propeller over the mandrel with the pushing face
of the propeller against the pitch block. You can adjust the height of the propeller on
the pitch block by using spacers between the bottom mandrel cone and the mandrel flange.
Ideally the propeller should be centered on the pitch block if it is not cupped. If the
propeller has a cup you should let the cup overhand the relief area cut into the pitch
block to accommodate the cup. Lock the propeller against the pitch block.
4. Use the rawhide hammer to work the propeller to the block.
Start in towards the hub and work your way out to the outer edge of the propeller. Once
the propeller fits within approximately an eighth of an inch from the block, you will have
to use a leather belt or strap between the propeller and the block to give you a fulcrum
point to bend the propeller over and overcome spring back. This will allow you to obtain a
more exact fit to the pitch block. Once the propeller is laying down against the block,
use the dead blow hammer to take any slight flaws out of the blade - four or five hits are
usually all that is needed per blade.
On stainless or bronze wheels you can use the copper hammer
to feather in the outer edges. If the propeller has a cup you can bend the cup over the
relief cut in the pitch block or you can obtain a softer roll by placing the leather belt
or strap under the trailing edge and bend the cup over the belt or strap.
After all blades are shaped to the block, draw a line around
the best blade on the pitch block and compare the other blades to the profile.
When repairing stainless steel propellers some will require
the use of heat to bring the propeller back to its original shape. When heating stainless
do not exceed 1700 degrees Fahrenheit. At 1700 degrees Fahrenheit, the grain structure of
the metal changes. A 1700 tempstik can be touched to the area being heated and will melt
when the metal reaches 1700 degrees. You will find the heated area to e Dull Red in color,
and the propeller can be worked to the pitch block. A standard oxygen/acetylene torch
works quite well. This allows you to heat only the area that is bent and makes finishing
the propeller much easier.
Most bronze or brass inboard wheels will bend cold. If heat
is required to repair these, care needs to be taken to prevent breaking the blades.
The temperature should exceed 1400 degrees Fahrenheit before
repairing. Most alloy bronze propellers are extremely brittle between 700 to 1400 degrees
Fahrenheit. Use 1400 degree Fahrenheit tempstiks to check the heat before striking the
propeller with a hammer. Always heat the propeller from the hub to the outer tip using a
#4 or #6 rosebud torch, this will evenly heat the entire blade. Then work the blade to the
pitch block using either a rawhide or copper hammer. Push the blade to the block or tap it