The center of the mounting post and the end of the sanding device (above left) is set to the length of the prop size. This dimension is now six inches to allow a twelve-inch full blade length. The prop nut is only there to hold the ruler in place. The original prop (above right) is too long for Allen’s engine/model setup. He now has the prop in place to do the dirty work to shorten the length. Allen holds
the prop in place (below left) while he works the sanding block in a fore and aft movement perpendicular to the prop length. This should be done slowly. The prop is now sanded (below right) to the length desired. Be sure to clean up the carbon fiber remains as they can be a pain to your skin. The ends can be secured with CyA to prevent unraveling.
same length. After much thought, I found a flat 2 × 4 × 18-inch length of wood in my stash at home. I also used some hard maple motor mount stock and some 4–40 self tap- ping screws. The screws I chose were 3⁄4-inch in length.
I wanted to be able to adjust the length of the prop blades so I permanently attached a pair of motor mount stock to the wooden frame, centering each about six inches from the end of the frame. I had a third length of motor mount stock and set the clearance be- tween the two permanent pieces so the third portion would slide fore and aft. The third or middle piece of motor mount stock was
drilled in two places. I was able to insert a 1⁄4-inch dowel in one hole and a 5⁄16-inch dow- el in the other.
FLYING MODELS
The dowels were set apart by an inch or two and would be used for different prop shaft sizes. I would place it one way for the smaller diameters and turn it around for the larger shafts. Holes were drilled in from one side to allow another set of 4–40 × 3⁄4-inch self-tapping screws to be able to hold the center motor mount securely in place. At the end of the wooden bottom brace another mo- tor mount was glued and screwed down so there would be a table to hold the end of the prop to make sanding easier.
First, I needed to decide how short I want- ed the prop blade to be cut in length. I used the shaft size that was correct for my prop center hole. I had to measure from the cen- ter of the holding shaft to the end of the sanding wooden base. Then I tightened the
set screw in from the sides so the center mo- tor mount would not move. The prop tip was moved to the end of the sanding area and with a perpendicular sanding motion I slow- ley shortened the prop blade from its origi- nal length to my desired length. Once the one prop blade was the correct size, I moved on to the next blade.
This will work for two, three, four or more blade props. Sand each one to the same length and then remove the prop from the fixture. You are now working with blades that are equal in length and much easier to balance. Always sand off any prop material from the front of the prop as doing different- ly will change the pitch of the blades. The ac- companying pictures should help clarify my written narrative.
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