Spline Loft Sculpture

ZooHead

Well-known member
One of our forum members, GS098, is an artist and sculptor with no 3D modeling experience.
He is trying to incorporate Cheetah 3D in his workflow to facilitate laser cutting materials.

With no experience, just placing the splines is hard work. (y)

This process has some real promise for laser cutting but I don't have a laser cutter myself so I have no way to test it.
Hopefully GS089 will prove it one way or the other in the end, which won't be for a while, no rush no deadline.

These splines represent most of the elements, like cross sectional slices.
The first thing to do is to separate the splines according to object.

sculptsplines.gif


Notes on laser cutters: They don't do beveled edges so it's butt joints or sanding I guess.
 

ZooHead

Well-known member
After separating the splines for the element named Quadrat,
I changed the type of spline to Linear since these are linear forms.

This will also show more clearly the spline colors which will tell us
where the joint point is as well as the winding sequence direction.

quadrat_splines.gif
 

ZooHead

Well-known member
If the joints and direction between the splines don't match, and you
add the splines to a Loft Creator, the results could look like this.

Quadrat loft 01.jpg
 

ZooHead

Well-known member
Since only one spline is out of order, reverse and rotate it to match the others.
To flip the normals look in the Loft panel.

quadrat_loft.gif
 

GS089

Member
Wow, great, I see a different workflow to my try and error method... thanks a lot! I will try your workflow. One thing, i my project file the whole sculputure is streched on one axis, so what was a square (Quadrat) is not a square any more, I wanted to get more space in that axis. I dont know if my chosen factor is final, it will be something between 1,5-2,5.
 

ZooHead

Well-known member
I did see some differences between your splines and the paneled version.
When you change scale it can be done in multiple ways.

Of course every new user will scale with the Transform Tool in Object Mode
and if scaled evenly in x y z you may never realize this is not the way to proceed.

At least not without using the Burn Transform or Burn shear/scale commands
in the Coord System panel which will return your object to 1x1x1.
Burn Transform will also put the pivot point at world center.

If you look at the panels you placed on Quadrat that are not 1x1x1,
and try to rotate one of them you'll see the weird behavior.
Burn shear/scale and try again.

The usually correct way is to scale selected polygons
in Polygon Mode so your objects stay 1x1x1.
 

GS089

Member
So, my first mistake was to start with polygon planes? How do you convert these planes to splines?

To illustrate my first steps:
I draw the figures in illustrator, above the original painting, then I imported the illustrator svg in Cheetha3d, then I made the elements editable, move the coordinate system in the middle of that element und turned it 90 degree... then I place the planes with snapping inside the imported svg. Btw. the impoted illustrator svg were splines, so I should have worked directly with these elements instead of planes?
 

Helmut

Well-known member
* No idea about your work flow / modus operandi but:
* Polygons - as splines - can be simply generated in C3D via the menu command n-Gons.
* You just nudge those around to get a flat base.
* You then stuff these profiles into the hierarchy of a Loft creator.

Screenshot 2022-05-18 at 18.15.56.png
 

ZooHead

Well-known member
So, my first mistake was to start with polygon planes? How do you convert these planes to splines?

To illustrate my first steps:
I draw the figures in illustrator, above the original painting, then I imported the illustrator svg in Cheetha3d, then I made the elements editable, move the coordinate system in the middle of that element und turned it 90 degree... then I place the planes with snapping inside the imported svg. Btw. the impoted illustrator svg were splines, so I should have worked directly with these elements instead of planes?
With the Loft Creator and your cross sectional splines, there's no reason
for individual planes that will be merged together at the end anyway.

The Loft Creator will also let you cover the ends if you want.

What I don't know is If the UV pdf will be accurate and work for laser cutting.
I think it would be smart to run a test all the way to the end and see if the pieces fit.

The Idea I'm working on will utilize the pdf vectors for precise cuts and utilizing
a raster image for engraving the labels. I have to figure out flipping
the uvs so the labels and cuts will be from the back.

And you have to figure out if you can set the scale accurately
in Illustrator or more likely in the laser cutter software.
 

GS089

Member
The lenght of the whole sculpture should be 291cm. Dont you have absolut numbers in Cheetah for dimensions? But you can reverse engineering like placing a plane, export it as pdf and then have a look how big it is.. and then calculate the factor to increase/decrease the 3d model?

The format for the laser cut can be just an pdf. The teeth for joining I usually did in illustrator.
 

ZooHead

Well-known member
I just found the folder named group, that all other folders are in.
These folders are full of objects and splines, and the Group Folder was scaled to 1x1x1.5.

So when I copy and paste a folder from within this Group Folder, every thing is reduced by .5 in one direction.
This is why my object matches your original form and not the altered one.

Now that I found that mistake, I can tell you not to do that.

The rule is always return to 1x1x1 scale, shortcuts like this will cause big problems.
Think of it like this, one person is tall and another is short, but they are both 1x1x1 in scale.
 

ZooHead

Well-known member
The shortcut method I would use is to do the 1.5 scaling within the Loft Creator.
When I'm done with any tweaking of the splines, I make it editable.
Then the first thing I do is a Burn shear/scale or Burn Transform command.
 

ZooHead

Well-known member
I have been unwrapping the Quadrat object over and over
again to learn as much as I can about how Cheetah behaves.

I used to think if I unwrap an object with either algorithm,
the relative scale would remain the same.

Besides making the mistake of unwrapping while polygons are selected,
which only unwraps the selection, usually on top of other uv islands.
I found I was wrong as you can see in the image.

unwrapping problem 01.jpg


The problem can be corrected by snapping, pinning and unwrapping the selected
Island again, but it shows each uv island may be scaled slightly differently.

Going through all this crap as a new user is not looking good.
I was able to get the best unwrapping done in what I'm going to call Pinwheel fashion.
By finding a point of double symmetry, and keeping it all connected, It looks pretty good.

unwrapping solution 01.jpg
 

ZooHead

Well-known member
Bad news again. The two sides are identical and should be the same length.
With what I'm finding, I wouldn't trust this method for laser cutting.

unwrapping problem 02.jpg
 

ZooHead

Well-known member
The lenght of the whole sculpture should be 291cm. Dont you have absolut numbers in Cheetah for dimensions? But you can reverse engineering like placing a plane, export it as pdf and then have a look how big it is.. and then calculate the factor to increase/decrease the 3d model?

The format for the laser cut can be just an pdf. The teeth for joining I usually did in illustrator.
Remember, the size of the object or polygon has no bearing on the size of the uv's.
You can "unwrap" a single polygon and it will fill the uv window, no matter what size the polygon is.
So each polygon will fill the uv window so each is scaled differently.

You would end up with a bunch of pdf's and would have to scale each one individually in Illustrator or another program.
If you can figure out how to handle resizing, it could still work by combining all resized pdf's into one.
 

ZooHead

Well-known member
Every time I use a tool I learn something new. Like the Loft Creator I have been using to make the Quadrat object.
The original object was made with all square splines and later scaled in width to 1.5.

I used the square splines to make the object with the Loft Creator, and it's a good thing.
If I had tried to use the Loft Creator with rectangular splines it would have skewed two of the sides.

Loft skew.jpg
 

ZooHead

Well-known member
To make the next object "brücke" or bridge I'm going to show
the panel snapping method that Gerald has already tried.
I only need to snap panels to the outer edges.

Brücke splines.jpg
 

ZooHead

Well-known member
You only have to make one plane, snap it to the splines, and the rest will be built from that first plane.

bridgebuild.gif
 
Top