- [Instructor] I've noticed some common pitfalls that
beginners fall into, so let's talk about what some
of those common pitfalls are and how to avoid
them with some best practice examples.
Pitfall number one.
Insufficient or negative draft.
I'll open up this first part separately
so we can see it better.
It's a mind bendy at first.
But think about this for a minute.
If the direction your mold comes apart in,
is straight up and down and your part doesn't have
enough draft, it won't demold properly and you might
end up with some unusable parts.
Negative draft is almost impossible to remove
with a hard mold.
If your plastic hardens and you start trying to pull it out,
what do you think will happen?
Watch out.
There's a handy tool in SolidWorks that will help me
visualize this.
It's found here under the mold tools tab.
If you don't see it, right click, and you can select
it to make it visible.
The tool I'm gonna use is the draft analysis tool.
I can usually tell by looking, but this tool can help
you really zoom in on those problem areas.
If your part design requires some negative draft
or undercut, your mold will require additional moving parts
to your design.
I select the parting surface here and it shows me that my
part has three degrees of draft.
Green is good,
yellow needs some work,
and red won't work.
So if we look here with this undercut,
this will call for a separate part of your mold
called a pull, so that this whole part
can come out correctly.
The addition of pulls and other moving parts
in your mold definitely add costs.
So be mindful of that.
Another pitfall to avoid would be long, spindly things
and major discrepancies in part thickness,
as shown in this sculptural object.
Material takes less time to cool the thinner it is.
And parts thicker than the recommended maximum,
start to warp in shape.
You can mitigate this with tapering between parts.
But you should pay special attention to your manufacturers
guidelines on what's actually possible.
Let's say we wanted to mold this sculpture.
Then spindly features tend to stick in the mold.
If you have spindles, try to design them along
the parting plane so you have a chance of getting
them out.
Different thickness of parts solidify at different rates,
which can make your part shrink at different rates,
and deform your parts often outside of tolerance.
Also, the longer it takes for a part to be made,
the more expensive it is per part.
These are some of the reasons why well designed parts
have a nominal wall thickness that is consistent
throughout the entire part.
The third design pitfall that I want to call out
are lattice vessels.
Like this one.
I've had quite a few people ask me how to mold
something like this,
and I have to explain why this is extremely
complex to mold and manufacturer.
3D printing helps us create some really cool
geometries without the considerations required
for mass production.
Keeping a design manifold with sufficient draft,
filets, and flow consideration is hard enough without
your design being full of a holes.
I could quite possibly mold this lattice vessel
in two pieces and assemble it later but the draft
would get very complex.
If the design requires this to be a singe part,
the interior volume makes this a destructive
molding part by nature.
Of the manufacturing techniques we've covered,
what do you think would be the best way to make something
like this?
The last novice design pitfall I'll cover
are improper wall transitions.
At first, this looks fine.
But on closer inspection, the two walls are different
thicknesses and where they meet is incorrect.
Maintaining a nominal wall thickness applies to
where parts of your model meet up in every direction.
If you have two same thickness walls, meaning up and
a 90 degree angle, the hypotenuse right here is too thick.
Your corners are going to warp.
If you have two same thickness walls meet up,
but your rounded corner has the same radius apply
to both interior and exterior,
you can see it does get thicker in that corner.
I tend to address this on the sketch level,
where I describe the inner wall required,
apply the radius and then offset that line.
That way I can control where the interior wall goes.
I also really like the shell command.
It's really helpful for a lot of starter projects to
help solve the thickness variation issue.
At its core, you need to pay careful attention to
the way liquid flows throughout your mold as well
as what level of difficulty there will be at ejecting
your part once it's solid.
Practice makes the master and prototypes are a lot
cheaper to experiment, so go have fun.