Re: ATM Aluminum, Split Ring, Astrograph

[Ak55c@aol.com]

In a message dated 4/24/00 8:17:44 PM Eastern Daylight Time, mjc5@psu.edu 
writes:

<< Is there ever any problem with the dissimilar metals? 
 Stainless would certainly be tough, but I'd worry about 
 expansion/contraction effects. Now of course I could be full of 
 balony too! ;^)
 
    What about a ring made entirely of steel, and then case hardened? >>

Hi Mike,
     In response to the above, the coefficient of thermal expantion for the 
austenitic
grades of stainless (eg the popular 300 series), is virtually identical to 
that of
plain carbon steels.  They weld together beautifully when using a stainless
filler rod.  I have been welding stainless and plain carbon steel for years 
and
have had no negative results.  Case hardening plain steel would be more costly
than using stainless and and would result in a ring bearing surface that 
would 
be prone to rust unless you plated it (eg nickle plating).  I chose
304L stainless for my ring because of its high  stregnth and good welding
characteristics.  I painted my entire ring except the face that rides on the
rollers.  Aluminum should  not  be a consideration  in a larger scope
due to its poor wear characteristics even in it's fully tempered state.  
There are many metal fabrication shops that would make up a ring such as
this for a reasonable price.  I received quotes in the $500 range for such a
ring in 48" diameter.