prop shaft couple set screw dimples

Comment

Comment by bob mitchell on September 15, 2014 at 7:48am

Grades of Stainless Steel

To make a steel "stainless" it needs to contain a minimum of 12% Chromium (Cr). The Cr oxidises in the atmosphere forming a passive  layer on the surface. This layer, unlike coated steels, is self repairing           should it be scratched.

The problem with 12% Cr is that it is fairly brittle and only provides  the minimum corrosion resistance. Increasing the Chromium content to 17% improves corrosion resistance but increases brittleness. Adding           8% Nickel makes the steel ductile again. Thus 18/8 stainless was born (304). 316 / 316L has additional Molybdenum and higher Nickel which provides greater corrosion resistance.

With stainless when you see two numbers they always refer to the Chromium and Nickel content - 18/8 is 18%Cr and 8%Ni. If you see 3 numbers like  19/12/3 they refer to the Chromium, Nickel and Molybdenum content. 316   is 19%Cr, 12%Ni and 3%Mo.

        Welding Stainless

There are 2 common grades of stainless: 304L (welded  using 308L filler), and 316L which is welded using         316L filler.

Stainless is easy to weld but very difficult to keep flat, the coefficient  of linear expansion is 1.7 times that of mild steel. There isn’t   much you can do about that except to weld it quickly and by doing   so minimise the heat input.

304 and 316 (as opposed to the L low carbon versions)    suffer from weld decay. When heated to welding temperatures the Chromium   combines with the Carbon leaving the steel short of Chromium and therefore         unable to self repair itself.

REFERENCE FROM MIG WELDING

Comment by bob mitchell on September 15, 2014 at 2:08am

I bet THAT boat was hoppin'.

Comment by Clyde A. Phillips on September 14, 2014 at 9:38pm

That's a no-brainer: you have the ability to do it yourself (otherwise I would advise you to have it done), so fill the dimples and dress them done (turning them down is first choice) and start from scratch. 

Calder is a good source and his advice is good.  I had a shaft pull itself out one time.  This was on the research vessel I ran for Rutgers, not a Newporter.  Seas were at about three feet (we'd go out and work in them but that was our limit, though we would work in four foot seas if they built to that after we started in three or less feet.  On this boat the rudder stopped the shaft with about a quarter inch still of the shaft in the engine compartment, preventing a leak.  I was able to get hold of the shaft with a large vice grip and move it back into the after half of the coupling which was reasonably easy to do--after I found the key in the bilge water which was sloshing around while the boat lay broadside to the seas.  Set up your setscrews in fresh dimples and forego the problems.