"RichZ" wrote in message
...
On 4/23/2010 10:48 AM, Bob La Londe wrote:
I just finished machining my first injection mold the other day, and
have various supplies ordered to experiment with.

Based on reading various threads I think I already made one mistake with
my prototype. I don't think I have enough reservoir built in to account
for shrinkage during cooling. Not that big of a deal to fix though I
think. The first one was a prototype to figure out how to machine the
mold. I figured I would run into some issues with this first one.

Upon reading the various manufacturers websites it seems you are
supposed to get a decent laminate bait by just taking to two injectors
with nozzles to match or a mating manifold and injecting the liquid
plastic side by side into the mold.
1. Does that give a decent uniform Laminate?
2. How would you make a laminate that is other than 50/50? Just use two
different diameter injectors?
3. Why doesn't it swirl when you do that? Particularly in a detailed
mold?

Core Shot. Another site I read says you can get a core shot affect by
just filling the mold with your main color and then shooting in a
different color. How does that work? If that doesn't work, how about
using a basting syringe, inserting it into the mold and then
withrdrawing it as you inject plastic in the core of the bait?

If the laminate method listed above does not swirl, how do you get swirl
pattern baits?



Two injectors makes laminates. Usually injecting into the sprue, one on
each side of the parting line. Almost impossible to use two different
nozzle sizes and get non-50/50, because the injection stroke would be
different, unless you also had different diameter injection pumps.
Projections that come into the flow of the plastic more than about 40% of
the diameter will cause mottling more than swirling. Swirl is done with a
'corkscrew' type vane in the sprue or at the nozzle.

Thanks Rich. I was looking at some of the dual injector manifolds. I could
make one easily enough. Maybe make it in two pieces just like a mold so it
can be unbolted and cleaned out easily. I ordered a cheap injector so I can
see what kind of O-ring they use. I imagine its probably teflon. Then I'll
just turn my own injectors in various sizes to play with on the lathe.
Hmmm... might be a good excuse to get a rotary chuck for the mill. LOL.