- This is the video you would come to if you modeled
something in a CAD program or downloaded something online
that was from the CAD program, you bring it in Meshmixer
and bad bad things start happening to your model
the moment you touch it and I'll explain why.
I'm going to go here to import.
I'm going to import a CAD model that I made
in Fusion 360, which is very nice
but I want to put some maybe adornments
on the sides here, so I'll go into sculpt
to draw the nice tool to create some volume on the mesh.
Good strength, refinement is turned on,
reduction so this should be a really nice tool.
I'm going to make my brush a little bit bigger
and I'll just start sculpting and my entire model
just starts freaking out, maybe I should go over
here and instantly I have something that is not printable
with reversed faces, inside out, just not good at all.
What happened?
Well Meshmixer really really wants to use triangles.
If I press W, you can see that my tool,
my draw tool has created a lot of these beautiful triangles.
It's actually creating more and more
and it is now acting as it should, I'm able to create volume
and sculpt like I should but I'm going to undo that
and go back to what this box started out as.
This is the view as it comes in.
I'm going to press W to go into wireframe.
Now you notice that here, in the cutout part,
Fusion 360, the CAD program
has created quite a few triangles.
That's great, if I use the sculpt tool on that,
press W again, it'll work pretty well, like I would expect.
Going to undo that, but the problem happens
when I go and try to use a sculpting tool
on two triangles, so if I turn refinement off
and try to do a draw command on this,
it makes the triangle bigger and it really doesn't know
what to do except make that triangle bigger
because drawing creates volume but with refinement off,
it's just essentially saying the only way
to create volume is just to make that triangle bigger.
I'm going to undo that.
What we need to do is get more triangles added to this.
You can also see up on top here,
that in order to create this cylinder cutout,
Fusion 360 just started all of these little triangular lines
I'll press the C key and zoom in, right here
at the corner and they just essentially ray out
until it defines these edges, so that's great.
There's some triangles here but even these triangles
are not good ones because this is a single skinny,
but large triangle going from here to here which is why
if we run the sculpt tool on these triangles,
bad things happen again, I'm going to undo that.
We need to get this to be more detailed.
The way to do that most easily is to go
into select, I'm just going to hit ctrl+A to select
the entire box and go up here to edit to remesh.
Now even at the default, Meshmixer has remeshed it
into something that could be sculpted quite a bit.
That would totally work, we can turn up the density
quite a bit more, obviously Meshmixer has to think much more
about it at a higher density but this gives us
a result that is still within the areas
of margin for 3D printing but is something
that we could sculpt on, so now it's a very very dense model
that would react beautifully to sculpting.
That is certainly a way to do it
and I did that on the entire model.
You don't have to do that if you just want
to let's say get some more triangles
on just the sides and you don't really care
or you want to keep this part separate.
I'm just going to go into the select tool,
select these two triangles, these two, these two,
these two and let's leave the rest of them there.
These will cause some problems
as well but let's just do these.
I'm going to manipulate these but first I'm just going to go
and modify and create a face group just
to make it a little bit easier to select those again.
I'm going to go back into select, double click on it,
which selects the entire connected face group
and I'm going to go back in to say edit, to remesh.
We don't get a very good result with the adaptive density
because there's only two, there's nothing
for it to adapt to, so we would want to go down in here
to linear subdivision, so what this does is
it subdivides the triangles into more triangles.
As we take this up, it's trying to find out some,
these are essentially flat planes,
so it has to kind of guess a little bit on what to do,
but it adds more triangles in so that's good.
It essentially subdivides the two triangles
into four triangles and then a little bit more
and a little bit more and we can say accept.
Now we can go back in to edit, to remesh
with linear subdivision and turn it up again.
Even though these are pretty regular triangles,
they are now essentially more detailed than it was before.
We could try to sculpt on this, but now when we go
into remesh again, we can go into adaptive
or relative density, probably adaptive density here
and get a lot better result and turn the density up
and Meshmixer will think about it
and now we have something to work with.
As it thinks about it, say accept.
Now see we have a very defined top,
but the sides are now sculptable
and I can sculpt on them, so that is a way of doing it.
Now also, if sometimes you want to cut,
let's say a cylinder out of this, we can go into meshmix,
go down to a cylinder and just drag the cylinder
somewhere into our scene and it's not big enough,
so let's expand it like that and remember,
use the technique of the 90 degree of get it centered here
and obviously not the right size, move it down,
go to the top, squish it down, make sure it's going
right through, that looks pretty good.
Now, if I want to boolean this out,
if I want to cut this cylinder through the other one,
I'll go into my objects browser, I will select
the box first, my cutting tool second
and boolean difference and ooh,
really not good things happened.
You clicked on boolean difference, nothing good happened.
The reason why is because when I stretched this out,
it created this cylinder, but this is one triangle
that goes all the way from here all the way to over here
and Meshmixer doesn't know how to do a boolean
with one triangle like that, so I'm going to even just hide
the box for right now by turning off this little eye.
I'm just working on the cylinder
and I can do the same thing.
As I go in here, I click on one thing, do ctrl+A
to select the whole cylinder and go up here to edit
and remesh and even at adaptive density it works
but generally with CAD models, you would want
to do linear subdivision so that gives a lot more triangles.
Click accept and go back into remesh
and now when I do adaptive density
and I can make this turn up a lot more,
I will get a pretty good representation of that cylinder.
If you look and see, it's pretty pretty nicely formed,
I'm going to accept that, going to bring the box back in,
click on the box, click on my cutting tool
and do a boolean difference and now
that has cut really well through because,
I'm going to cancel this, the density of this mesh
is somewhat close to the density of that mesh
with a lot of triangles and that's
how you're able to do boolean.
You don't run into this problem all the time
just with CAD models that you import.
You can run into it when you Meshmix,
if I go back here, when you Meshmix in objects
and scale them, you only get a few different triangles.
I'm just trying to select this
and it's very hard to select all those triangles.
That's some techniques you can use
to not have your CAD models freak out so much
and be also selective in what parts you refine.
You see here, there's some refinement but the edge
got kind of a little bit beveled with this refinement.
But because I made these a face group,
it only remeshed these, the beautiful sphere
that was cut out in CAD isn't messed up at all.
Using selections and face groups can help you modify
parts of your model, if I were really going to be using this,
I could sculpt on this and make sure to click
the hold boundary to only sculpt inside of this
because the moment sculpting spills over
into the top of this block, this is such a large triangle,
that bad things would start happening.
If you really are dealing with a model like this,
I will hide the cylinder, you can go
into something like sculpt and draw.
If you go like this, bad things will happen.
I will go back in and if I say sculpt, turn on refinement,
sculpt and if you draw over this, your model messes up again
so make sure that if you are working on areas like this,
that you have a face group here and you go to filters
and say, restrict to group and now as I'm sculpting on this,
it just won't spill over all that much
into other groups as much as you might want.
I'm going to undo that, you would want to do also
hold boundary, so now the boundary of this group is held.
You still get a little bit because we're not holding
the boundary of the other groups,
but it helps do some sculpting on different sides
without changing too much of your model.
That is just an overview of how to work with CAD models
and do some linear subdivisions to give you
some more geometry to do cool things in Meshmixer
and also, one final note, I apologize,
you can go very easily from CAD model into Meshmixer,
into a polygonal mesh, but it's very difficult
to go back from Meshmixer into a CAD model.
It's because these facets were created just
in this file format as an STL but in the actual CAD model,
this is just an elegant sphere,
I never see any lines at all.
Bringing this back into a CAD model, if you could even do it
would turn this into a really complex CAD model
where it really doesn't want to work in this fashion,
so just remember that it's easy to go from CAD
into a polygonal mesh but going
from polygonal mesh into CAD is very, very difficult.