"Steve W." wrote in message news
Bob La Londe wrote:
http://tacklemaker.info/index.php?ac...sa=view;pic=31
You shouldn't need to be logged on to see the image.

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.


How about machining the ends to use something like size 50 motorcycle
chain. Basically a pivot on each half. Then machine in 2 more alignment
pins to ensure proper closure. That would allow you to start with 1/2".
Sort of how hinged hand cuffs work.

************

Yeah Steve I have considered a connecting link type design. I'm not
convinced its equal or better, but it would definitely reduce wasted raw
stock. Its a good idea.