Flatten a face

[Chris_G]

Hi,
I wanted to share a little trick.
A friend asked me if it was possible to flatten a face.
His version of SolidWorks didn't offer this feature.
This is a thin sheet of metal that is bent around a center block :

flatten-1.jpg (11.6 KiB) Viewed 6911 times

He wanted to get the shape of this flattened face, to cut it to shape before bending it.
Here is how I did it:
I discretized the profile curve with distance method :

Code: Select all

bspline.discretize(Distance = 0.2)

flatten-2.jpg (7.63 KiB) Viewed 6911 times

Then I created a curvilinear knot sequence :

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# pts are the discretized points
# dis is the discretization distance
params = []
for i in range(len(pts)):
    params.append(1.0 * i * dis)

Then I created an interpolating curve from these points and parameters

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bs = Part.BSplineCurve()
bs.interpolate(Points = pts, Parameters = params)

This way, for any point on the curve, its parameter is the distance from curve start.
Then I extruded the resulting curve :

flatten-3.jpg (10.36 KiB) Viewed 6911 times

The extruding operation also creates a curvilinear parametrization in the V direction.
So the parameters of this surface match realworld units.
Then I made the boolean operations to give the surface its final shape :

flatten-4.jpg (10.69 KiB) Viewed 6911 times

And it is now simply a matter of taking the 2d curves of all the edges of this face and "apply" them an a plane :

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#face is the face highlighted above
edges = face.Edges

# the list of 2D curves
curves2d = [] 
for e in edges:
    curves2d.append(face.curveOnSurface(e))

# apply the 2D curves on a plane
plane = Part.Plane()
for c in curves2d:
    Part.show(c[0].toShape(plane))

And here is the flattened face :

flatten-5.jpg (8.59 KiB) Viewed 6911 times

In case someone needs this one day ...
Chris

[microelly2]

Yes, its a nice and useful trick.
having linear and parallel vIso/uIso curves the surface is developeable.
this is a "generalized cylinder".
with some more calculation this can be adapted to "generalized cones" too (vIso curves are lines and go all to throught the same point)

For me the question is: How to detect areas on a surface that are cylinder or cone like.
the theory is obvious the principal curvature must be zero, so one has to find the areas with curvature 0 to get developable subsurfaces.

thanks for the tipp.

[Mark Szlazak]

Thanks Chris!

This gave me an idea for a CAD challenge. It's a reverse of what you did.
If you start with a flat plane in CAD then can you fold it with CAD operations to make some origami?

This was made from a single sheet of paper.

Origami_spring.jpg (224.52 KiB) Viewed 6892 times

[microelly2]

This gave me an idea for a CAD challenge. It's a reverse of what you did.
If you start with a flat plane in CAD then can you fold it with CAD operations to make some origami?

this task is solved partially by the sheet metal workbench.
you start with a planar sheet and fold it to a shell.
at the moment there is no support for rolling the plane to a cylinder or a cone
it's an interesting task too

for paper work I have this macro
freecadbuch.de/doku.php?id=blog:papiermodelle_erstellen

of course origami is a nice task, but the main problem is to unroll/unfold a Shell.
If the way to unroll it is found you can bend and roll back from the plane to the volume going the trace back.

[Jee-Bee]

at the moment there is no support for rolling the plane to a cylinder or a cone
it's an interesting task too

As far as i remember it isn't in Pro-E Creo (or i didn't know it) but in Creo there is one verry nice sheet metal feature and that is convert to sheet metal and that works well with cilindrical sheet metal

[Leatherman]

Thank you for sharing!

[bennn]

Hi all,

I took inspiration from Chris and created this little macro that unrolls a face or solid. This is more oriented toward wood/foam machining, for snowboard or kiteboard core manufacturing for instance.

Let me know what you think. If people find it useful I'll add it to the wiki.

This is my first Freecad macro, so I'm definitely open to criticism !

[TheMarkster]

Hi all,

I took inspiration from Chris and created this little macro that unrolls a face or solid. This is more oriented toward wood/foam machining, for snowboard or kiteboard core manufacturing for instance.

Let me know what you think. If people find it useful I'll add it to the wiki.

This is my first Freecad macro, so I'm definitely open to criticism !

Looks interesting. Can you upload a simple model demonstrating its use?

[bennn]

If you open that project attached, you'll find a bent volume, generated with bezier surfaces.

If you select all edges that need flattening, which are the edges along x axis, starting with the reference edge, which is one of those that are supposed to be flat - typically the bottom ones if you want to cnc a part -, and run the macro, you'll get a flat part.

Let me know if that works !

[TheMarkster]

I had to add these 2 lines to the import section:

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import numpy
from FreeCAD import Base

Otherwise I was getting the message about selecting the edges, which was masking the real issue (numpy and Base being undefined).

One thing I was interested in was flattening out this object just to see if it would give me a better way to judge the uniformity of the groove.

cam-groove.png (17.67 KiB) Viewed 5789 times

I was able to get these 2 faces:

cam-groove-faces.png (5.84 KiB) Viewed 5789 times

which I got by selecting the 2 innermost edges and running the macro twice, swapping the order of selection each time. It didn't really help me as far as determining whether the groove was uniform, but an interesting result all the same.

As to how useful the macro would be for its intended purpose I'm not the one to judge because I don't do that sort of work.