[modeleng] Re: Against the grain

  • From: Jesse <fernj1@xxxxxxxxxxx>
  • To: modeleng@xxxxxxxxxxxxx
  • Date: Sun, 15 Apr 2012 15:40:57 -0500

The "grain" in metal is actually the crystaline structure.  When I 
worked at the CONALCO aluminum rolling mill in Jackson, slices of each 
billet were routinely sent to the lab to have the grain structure 
analyzed.  Heaven only know what sort of acid bath they used, but the 
resulting slab's face looked like galvanized steel.  Out very near the 
edges of the billet,where the metal had cooled quickly, the grain 
(crystal) was very fine, but as one looked towards the centre of the 
slab the crystals became larger because the metal had cooled more 
slowly.  A nice side benefit to the samples at the lab was that they 
were all different thicknesses and when they were through with them, we 
blokes in the machine shop would glom onto them to make various and 
sundry things for ourselves.

Jesse in Troy, TN where rain is expected tonight.
> We all know that wood has a grain, and most of us will have read that
> metal does too.
> However, you can go for a long time without noticing it or it being a
> problem.
>
> I cant remember the last time that the grain in metal caused me any
> trouble, until today.
>
> I needed to do a simple turning job.
> What it ended up as was:
> a piece of steel, 1" at 1/4" dia, then 3/8" at 0.600 dia, and then 1/2"
> of 1/4" dia.
>
> In one of the "junk" boxes I have some 4" lengths of 3/4" steel (of
> unknown specification) with surface rust, so I decided to use one of them.
> Put in chuck and turned down about half the length to get back to a nice
> clean surface.
> Then reversed in chuck to do the same from the other end.
>
> The first end had a superb finish, and looked excellent.
> However, the other end looked as if it has been chewed away by a rat!
> Same tool, same setting, same feed and speed.
> I then tried several different feeds etc, but nothing I tried enabled e
> to get a decent finish on the "rough" end.
>
> Ahh well, enough playing about. Reversed in chuck, and turned the 1" and
> 3/8" lengths, so they ended up with a decent finish.
> Then reversed again and turned the 1/2" length (of 1/4" dia).
> Finish lousy, but it didnt matter for that particular section.
>
> Having made the part, I then tried another piece from the same batch,
> and found exactly the same effect.
> I assume that it is a heat treated steel, and must have a particularly
> coarse grain structure.
>
> Unusual, and consequently, interesting.
>
> Alan
>
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