REFLECTOR: Gear Fork Polishing and "the joys" of doing things yourself.

[Greg Poole]

Thanks for the detailed response Kurt - much more detailed than if I had answered, but fits my understanding and reasons for polishing - exactly. I polished mine with the belt sander that fits on my grinder - but with the green belt material then a buff. When I get the new improved nose fork it will also be polished to a "chrome like finish" to make it easier to clean, better looking, and stronger through the elimation of scratches and casting flash - but next time I too will use a professional metal polisher at a chrome shop than spend the hours of messy mucking around doing it myself. The shops that polish metal have the professional gear and the more effective polishing compounds to get the result far faster than yours truly.

I am quickly learning that there are some things that are simply not worth doing. I recently stripped and reconditioned a set of old Cleveland brakes & rims for another project and after looking at the time to strip, polish, paint, put in new bearings, lube etc,  would probably have been better off avoiding the personal time & frustration input by buying a new set of Groves or Clevelands. I know I would have been much further advanced if I had of done this.

As for chroming aluminium - IMHO; don't bother. I was once part of the street rod fraternity and the majority of chromed alloy ended up bubbling and peeling. Chroming also added extra weight and expense for no real benefit and there was always the question of hydrogen embrittlement unless the part was properly heat treated afterwards (cannot remember if this applies as equally to aluminium as much as it does to steel...).

Greg in Sydney.
  ----- Original Message ----- 
  From: NMFlyer1 at aol.com 
  To: reflector at tvbf.org 
  Sent: Tuesday, June 15, 2004 11:51 PM
  Subject: Re: REFLECTOR: Gear Forks


  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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