This will be old-hat for you mold guys but when hand-blending a
two-piece mold (female cavity that is blind when the halves are
together) what is the common technique for getting the parting lines on
each half to line up correctly?

Joe

wrote in message
oups.com...
This will be old-hat for you mold guys but when hand-blending a
two-piece mold (female cavity that is blind when the halves are
together) what is the common technique for getting the parting lines on
each half to line up correctly?

Joe

..

Common practice is to try not to hand blend. Machine it to size, then polish
out the tool marks.

I don't completely understand what you're asking. If that didn't answer your
question, let me know and I'll take another stab at it.

If you can't machine dead nuts accurate for a curvy survace (curved
parting line) then how do you hand blend the line together to get less
irregularity of the parting line? Perhaps prussian blue on one half at
a time and then blend the proud material?

Joe

wrote in message
oups.com...
If you can't machine dead nuts accurate for a curvy survace (curved
parting line) then how do you hand blend the line together to get less
irregularity of the parting line? Perhaps prussian blue on one half at
a time and then blend the proud material?

Joe


OK, lets make sure we are using the same terminology.

The parting line is usually a flat surface where the Cavity plate ("a" side
of tool) matches the Core plate ( "b" side of tool). It is possible for that
usually flat plane to be of some strange 3d shape, but let's assume that
it's not.

It sounds to me as if it was necessary for you to cut some of the concave
(cavity) surfaces into the "a" plate, and some into the "b" plate. Where
these plates come together will create a line on the part that will show up
when the mold is opened. If the contours do not match perfectly at this
point, it will create a step on the part that may be unacceptable. If I
understand your problem correctly, you have such a step that you would like
to polish out.

All of our molds are built on CNC milling machines and/or EDM's. We machine
these contours as closely as possible. We do not hand work those areas
except to remove .001 or less during polishing. If we end up with a step,
it's usually because of operator error. We will not hand work that step in,
we cut it again. The only way I would feel comfortable hand working that
area is if we could assemble the "a" and "b" plates and some how get a
dremel type tool inside, perhaps by removing a very large core block.

I'm not sure what kind of mold you're working on, or what your tolerances
are, but with an injection mold, ALL parting lines are visible. More than
..002 mismatch or so is often unacceptable.

Exactly. Except my CNC machine isn't super accurate and my part
doesn't need to have extremely accurate surfaces, it just needs to have
a nice clean parting line so I don't have to blend/sand/grind it after
molding. This is a composite part BTW so I'm not so worried about .002
like you are. I'm mainly wondering how to figure out what areas will
create a step shy of molding something a few times iteratively.

Joe