On 7 Jan 2016 03:58:45 GMT, "DoN. Nichols"
wrote:

On 2016-01-06, Gunner Asch wrote:
On Wed, 06 Jan 2016 10:01:00 -0800, pyotr filipivich
wrote:

Gunner Asch on Tue, 05 Jan 2016 14:36:39 -0800
typed in rec.crafts.metalworking the following:
On Tue, 05 Jan 2016 11:20:36 -0600, Tim Wescott
wrote:

On Mon, 04 Jan 2016 17:03:50 -0600, Terry Coombs wrote:

I returned those grates today , with an apology for not being able to

[ ... ]

Well, yeah, but where's the fun in that?

I mean, when casting news grates, one gets to try all sorts of new
things. It's "rec.metalworking" after all.

True indeed. If one wants to cast a new one...by all means. Wax
casting might be a good method. All one needs is 40 lbs of wax, lots
of green sand, casting box, and someway to melt down humm..50 lbs of
cast iron and then pour it into the mold. Simple!!!

And one could use the old one as a direct pattern!!

I believe that pattern makers have to use a "shrink rule" to
make the pattern a certain percentage larger than the desired casting.
And exactly what percentage is used is a function of what metal is being
cast. (Starrett used to list multiple shrink rules in their catalog.)

Enjoy,
DoN.

True, but some times the part grows rather then shrinks. Gray cast
iron, for example, has a stated shrinkage of from -2.5% to +1.6.
(note: a shrinkage of -2.5 is actually a growth :-)
--
cheers,

John B.