Steve Maas wrote:
> It's really hard to tell, from a picture, if something like this is a
> crack or just some kind of surface imperfection.
If I drag my fingernail across it, I can just barely feel it catch as it
crosses the crack. They only seem to appear on that one face of the arm,
which makes me think it might be superficial.
> (Cosmetic surface flaws that look like this are very common.) Often
> it's even difficult to tell by direct visual inspection of the part;
> sometimes you have to use a microscope, and even then it's hard to be
> sure. In general, though, real cracks don't meander the way the
> features in your pictures do, and usually you can see them extending
> into the perpendicular surface. I'd be 90% sure that the one nearest
> the center is just an anodizing flaw, but the one in the first jpg
> might be more worrisome. Can you find a microscope somewhere to get a
> better look at it?
Too bad my Dad retired 15 years ago, or I'd have access to a scanning
electron microscope... :-(
> Or, put some weight on it and at least inspect it
> with a good magnifying glass to see if it separates?
It doesn't seem to change under load.
> Of course, the conservative approach is to stay off it until you're
> completely certain it's OK.
Yeah, I have other arms I can use. I wonder if I could get one of the local motorheads to Magnaflux it?
--
-John Thompson (john@os2.dhs.org)
Appleton WI USA