On Fri, 15 Aug 2008 18:16:12 -0700 (PDT), the renowned
wrote:

I am building the Gingery plastic injection molding machine right now
and have a few questions for people who have already built them.

The heater block assy is CRS and you are supposed to drill and ream a
0.501 inch bore.
The plunger is CRS and is 0.5 inch rod, which we have measured at
0.5009 inch diameter.
What is a reasonable tolerance for the 0.501 inch bore, so that it
will inject the plastic (pmma and polycarbonate mainly) into the mold
and not leak around the plunger and squirt or shoot out the top?

I am concerned about similar metals and very close diameter to bore
clearance and having things gall up when I try to use the parts
together( it was usually aluminum not CRS), but I dont want the hot
plastic leaking around a loose gap.

You could look at the recommended tolerances on ejector pins,
typically in the range 0.3 to 0.9 thou (pins -0.3 to -0.6 and hole +0
to 0.3 thou).

Closer to the other limit, the vent depth (optimal depth varies by
plastic) is 1.5 to 2.5 thou for PC, and about a third of that for
runnier polypropylene.

Some other questions about the process.
With aluminum molds, what kind of mold release spray or material
should I use?
With an aluminum mold if I can get it nickle plated will this give me
a better surface finish, like on a plastic lens? If so what mold
release spray or material should I use with this material?

I read some great safety tips in some older posts on this group -
thanks for the heads up.

Anybody have a good source for 1-5 pounds of polycarb or pmma pelets?

School supply company or eBay.

Thanks,

Michael


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
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