Stainless Runners?

[Rolley]

Ice runners aside, I could never get stainless steel to take or hold an edge. I've always assumed that it was just too soft. What am I missing here?  I realize, of course, that "sharp" is a relative term applied to a 90 degree angle and that runners are sometimes actually too sharp for conditions, but you've still got the wear problem.  Does stainless slide better?   
Years ago there was talk about leaving sanding grooves perpendicular to the edge.  Anybody ever actually try that?  Inquiring minds want to know.

[Geoff Sobering]

The preferred stainless steel for runners is 440C. It can be hardened to Rockwell 60C, although I think runners are typically tempered down to about 54C. This hardness generally keeps an edge for many days of sailing.

To give you an idea of the how tough 440C is, here is a quote about it's machinability:

In the annealed condition this grade is relatively easily machined; approximately the same as for high speed steel. If this grade is hardened machining becomes very difficult and probably impossible.

Some runners (ex. slush runners) are made using 316 or 304/306 stainless because those are the only alloys commonly available in L and T sections.
Both of those alloys can not be hardened, so they are relatively soft and require more frequent sharpening.

Re: parallel sanding grooves - most people I know of have sharpeners with the belt running parallel to the runner's edge. Many people have reversible sharpeners so the belt always runs from the front to the rear of the runner. I don't know anyone who intentionally leaves scratches/grooves on their runners. Hand polishing to 600+ grit seems to be the standard practice these days.

[wnethercote]

Although I now routinely sail with 3/16 inch 440C inserts I previousl made a couple sets of 304 and 216 inserts, and am now making a new set of 1/4 inch 304 inserts, since I sold my previous set last year. My experience was that I needed to resharpen 304/316 inserts daily for hard ice conditions, but the daily sharpen was generally satisfied with a couple of the finer stones, rather than a belt sander.  My 440Cs can go a couple of weekends if I'm busy.

The 3/16 inch 304/316 inserts don't seem as 'stiff' as those in 440C, but I have to admit that 304/316 inserts are much easier to maintain for a casual person like me: the 440Cs are little more corrosion resistant than Sarns steel plates, so I'm inclined to bring out my 304s 0r 316s whenever we sail on salt water ice.  In fact, the first time i used my 440cs I treated them like my 304s and discovered a rusty mess when I looked at the runners the next wekend.  Ugh!

[Bob Gray]

    A very experienced heat treater told me that 440C is only somwhat rust resistant until it's hardened to Rockwell hardness 58. That's getting a little brittle for runners.
     I was glad to see someone brought up runners made from metals other then 440C. I'm convinced that only a very few top racers could tell the difference between 440C and other steels with identically profiled runners. You can buy a chunk of 304 big enough for a pair of runners for around $60. If you can find someone to cut the front side profile for you it's worth the money but I made several sets using a sabersaw  with bimetal blades. I used a 10" sanding disc from Sears on my table saw with 40 grit to put the 90 degree on the bottom, and a long bed belt sander to do the final sharpening and profile. I used baltic birch with formica over it for the bodies but there are other choices. The typical set cost me less then $100 to build.
     I have several sets of 440C runners but still use the 304 that are profiled for  special conditions. That being said, you can build a very competative set of runners without spending $700 or more.

[wnethercote]

Bob,

Exactly!  A hundred bucks buys you nine feet of 1/4 by 3 inch 304 flat bar.  My 440C runners cost me a thousand bucks for the three inserts alone, after shipping and taxes, albeit before the Canadian dollar rose to par ....

I cut the front and rear profiles of my 304 inserts with a good hacksaw and files and then do the running edge with an profile template, an angle grinder and my 3x90 inch sander. I too use baltic birch for the bodies with a light covering of glass or carbon and then attach 1 x 1/4 inch aluminum stiffeners (on edge) with epoxy and machine screws to keep the runners straight and chatter free.

3/16 inch 316 or 304SS inserts are more difficult because I can't get flat bar in that size.  The local metal guys typically shear the 3x36 inch blanks out of plate, and the locked-in stresses induced by the shear make the blank as straight as a dog's hind leg.  It's much more difficult to make a straight insert out of this than a piece of flat bar that's been cut off with a band saw!