http://tacklemaker.info/index.php?ac...sa=view;pic=31
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This is a pretty typical lead casting (sinkers, jigs, spinnerbaits, etc)
mold. The hinge shown works pretty darn well. It moves easily, and does a
good job of helping to hold the mold halves in alignment at the hinge end.
The opening (handle side) end has two alignment pins with radius ends that
mate the plates at that end. Over all my customers are atleast acceptably
happy with it. However to make a mold like this that finishes as to 1/2
inch (apx) plates with a hinge I start out by throwing away a third of the
raw material. Basically I start with 3/4 inch flat bar and remove 1/4 inch
to leave the 1/4" hinge bosses. It just irks me to throw away 33% of the
raw material on every one of these molds.

No. Bolting a flat metal hinge to the ends is NOT a better way. It simply
will not hold up over time, and even if its handled with kid gloves the heat
cycling will cause it to work loose. I've seen molds made by other mold
makers with tacked on hinges, and they get pretty beat up and very sloppy
over time. It often results in damage to the mold itself. Especially if
cores, pins, and other inserts or materials need to be placed in the mold
before casting. These one piece boss pinned hinges last through thousands
of heat cycles. I've done larger molds this same way that customers have
told me they have literally run tons of lead through. It would also require
another setup to drill and tap to tack on a sheet metal hinge.

Casting a billet with preformed mold bosses is not a great answer either.
The aluminum that results is more porous with the type of foundry I could
setup, and my quantity is to small to have them forged cost efficiently. I
think it might also drive up the per unit cost too much unless I could cast
or forge them in great quantities. On top of that castings or forgings then
have other machining that needs to be done to make them useable. One mold
company sells cast "blanks, but I absolutely hate to work with them because
the metal doesn't machine as nicely and the surfaces are more of a pain to
square up and also keep the hinges squared up with both haves coming out
aligned.

I did think of maybe using a third piece between the two plates with 4 pins
instead of the two I use now, but then it would not help as much with mold
alignment. It would also be slower and more cludgy for the customer to use
the mold. Every idea I come up with is also more manual work, or more
secondary setup work.

Maybe they way I am doing it is the best way to get a decent result within
my work constraints, but I can't help but wonder if there isn't a better
way.

Tangent:
If anybody is curious. No I do not use a round over mill to get the hinge
bosses. I tried that in the past and I was not happy with it at all. I cnc
mill a radius on the boss with a .001 depth of cut and then sand smooth when
it comes off the mold. It would be faster to use a round over mill, but
because of the lead on the cutting flutes and lack of consistency from one
to the next it would waste part of the useable surface of the mold plates.
Make larger mold blanks to make up for it then means slightly higher (few
cents per unit atleast) material cost and higher machine time clearing the
face of the blank. It works out to be a wash on that for cost and produces
a CNC cutting the radius gives better result in my opinion.