REFLECTOR: Gear Forks

[NMFlyer1 at aol.com]

The casting flaws are the rough appearance in the surface of the material. 
The most detrimental are the ones on the edge, in an area of particular load 
and/or vibration. 
Almost everything has casting, machining, or assembly flaws. Spam-can 
builders take lots of time de-burring all the holes they drill, and dressing the 
edges of every piece of aluminum they cut. this practice does not insure against a 
stress crack, but greatly reduces the possibility of it. 

The same care should have been taken on installation of the Plexiglas windows 
as well! 

The (quite pricey) block on my 4.3L chevy needed some attention to relieve 
stress points (casting flaws) in the crank webs. Again... insurance. 

Not to say that a nose gear fork would fail if it wasn't polished, but it 
will sure help it last to do so. 
I would guess that the design of the "old style" fork could have been 
sufficient if it was designed on a billet cut piece (which have flaws of their own), 
or on a polished or better cast piece. The only problem is, that adds a LOT of 
cost. Increasing the thickness of the piece can aide in reducing stress 
cracks, but polishing it will help even more. 

At a materials stress demonstration, the speaker took a piece of aluminum 
that was 2" wide, about 8" long and 1/4" thick. He scratched the surface with a 
pocket knife in the middle, then began his talk. As he was talking about 
materials stress, fatigue, etc, he was gently flexing the aluminum bar with his 
hands. Im not sure how long it was, but well into the talk, the 1/4" bar broke in 
half, right at the light scratch that he placed on the surface. Stress Crack 
run amuck!. 

There are many areas in construction of the velocity that will benefit from 
some polishing attention:
Basically every aluminum part that you put in the plane, but specially, bell 
crank brackets, canard hinge arms, hinges, rudder arms, nose fork, etc. 

I polish out my pieces with a scotch brite wheel on an angle die grinder. Use 
the finest wheel you can get away with. Gently take the sharp edges off of 
the corners, buff out deep scratches, de-burr the holes, etc.   

This practice will pay you back in longevity. 

 Kurt Winker
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