circle(161/2);

Hi all, I am modelling a top hat, and would be grateful for suggestions as to the most efficient way to extrude the basic oval shape of the hat over an arc. I am most of the way there with the basic shape with this: linear_extrude(height = 153, center = true, convexity = 10, scale=1.19875) scale([1,1.19255]) circle(161/2); The change I need to make is that the scale factor of the linear_extrude needs to increase from bottom to top, so it widens out over a curve - and the top of the hat flares out a little. I've done a lot of modelling in OpenSCAD but not played much with mathematical functions, so any pointers would be appreciated. I'd like to take this further, to also twisting the top of the hat, based on what I learn from this. Many thanks, Alex

Have a look at this code. It uses an exponential funktion. > pf = 1.004; > > for (i=[0:153]) > hull() > { > translate([0, 0, i]) > scale(pow(pf, i)*[1,1.19255]) > cylinder(r=161/2, h = .01); > translate([0, 0, i+1]) > scale(pow(pf, i+1)*[1,1.19255]) > cylinder(r=161/2, h = .01); > } in a more general formulation you would write your own function f to describe the trajectory. E.g. > step = 10; > for (i=[0:step:153]) > hull() > { > translate([0, 0, i]) > scale(f(i)*[1,1.19255]) > cylinder(r=161/2, h = .01); > translate([0, 0, i+step]) > scale(f(i+step)*[1,1.19255]) > cylinder(r=161/2, h = .01); > } > > function f(i) = 1+ pow(i/200,2); <http://forum.openscad.org/file/n17409/hat.png> -- View this message in context: http://forum.openscad.org/Curved-linear-extrude-tp17407p17409.html Sent from the OpenSCAD mailing list archive at Nabble.com.

Also consider approach where you draw the profile and build a volume of revolution Check this code for example to make handles: - http://www.thingiverse.com/thing:923244 (tricky to ensure they meet perfectly in the mifddle) Use inkscape to draw the profile: - http://www.thingiverse.com/thing:1065500 -- View this message in context: http://forum.openscad.org/Curved-linear-extrude-tp17407p17410.html Sent from the OpenSCAD mailing list archive at Nabble.com.

 // process mesh
 mesh_vertices = [ for(line=mesh) for(pt=line) pt ];
 mesh_faces    = mesh_faces(mesh);
 mv            = len(mesh_vertices);
 mvlen         = mv + len(mesh[0]);
 mv2len        = mvlen + len(mesh[0]);
 // process faces
 face_vertices = concat(mesh[0], mesh[len(mesh)-1]) ;
 face_polygons = [ [for(i=[mv:mvlen-1]) i ],
                   [for(i=[mv2len-1:-1:mvlen]) i ] ];
 polyhedron(
     points = concat(mesh_vertices, face_vertices),
     faces  = concat(mesh_faces,    face_polygons),
     convexity = 10
 );

I would use another approach. For curved surfaces I generally prefer to build the form from meshes of calculated points and compose everything with polyhedron. Here is a possible code: > n = 22; // oval points > h = 153; // form height > f = 1.19255; // oval factor > rad = 161/2; > // a simple oval shape in the xy plane > oval = [ for(ang=[0:360/n:361]) [rad*cos(ang), rad*f*sin(ang), 0] ]; > // a profile to be taken as a scale factor: change the function to your > taste > a = 0.1; b = 5; c = 3; m = 10; > profiler = [ for(i=[0:m]) 1+a*pow((i/b),c) ]; > // a rectangular mesh of points around the form > surface = [ for(i=[0:m]) [for(p=oval) profiler[i]*p+[0,0,h*i/m] ] ]; > > show_closed_mesh(surface); > //translate([2*rad,0,0]) cube(100); // just to confirm that CGAL consider > it a manyfold > > // generates a solid for a closed mesh adding two faces to close the top > and bottom > module show_closed_mesh(mesh) { > function mesh_faces(mesh) = let( n = len(mesh), m = len(mesh[0]) ) > concat( [ for(i=[0:n-2]) for(j=[0:m-2]) > [ i*m+j+1, i*m+j , (i+1)*m+j ] ] , > [ for(i=[0:n-2]) for(j=[0:m-2]) > [ (i+1)*m+j, (i+1)*m+j+1, i*m+j+1 ] ] > ) ; > > // process mesh > mesh_vertices = [ for(line=mesh) for(pt=line) pt ]; > mesh_faces = mesh_faces(mesh); > mv = len(mesh_vertices); > mvlen = mv + len(mesh[0]); > mv2len = mvlen + len(mesh[0]); > // process faces > face_vertices = concat(mesh[0], mesh[len(mesh)-1]) ; > face_polygons = [ [for(i=[mv:mvlen-1]) i ], > [for(i=[mv2len-1:-1:mvlen]) i ] ]; > polyhedron( > points = concat(mesh_vertices, face_vertices), > faces = concat(mesh_faces, face_polygons), > convexity = 10 > ); > } <http://forum.openscad.org/file/n17411/hat.png> The form is based on an elliptic oval and a scale profile. A mesh is built from them. The show_closed_mesh module is a very simple version of a more general version I coded. It takes only one envelope in the form of a (closed) mesh and closes it with two planar faces. If needed this two faces may be triangulated. -- View this message in context: http://forum.openscad.org/Curved-linear-extrude-tp17407p17411.html Sent from the OpenSCAD mailing list archive at Nabble.com.

Yes - this is exactly it, thanks very much. I will play about with it until I can properly use all aspects. Many thanks! -----Original Message----- From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of Parkinbot Sent: 24 May 2016 00:04 To: discuss@lists.openscad.org Subject: Re: [OpenSCAD] Curved linear extrude Have a look at this code. It uses an exponential funktion. > pf = 1.004; > > for (i=[0:153]) > hull() > { > translate([0, 0, i]) > scale(pow(pf, i)*[1,1.19255]) > cylinder(r=161/2, h = .01); > translate([0, 0, i+1]) > scale(pow(pf, i+1)*[1,1.19255]) > cylinder(r=161/2, h = .01); > } in a more general formulation you would write your own function f to describe the trajectory. E.g. > step = 10; > for (i=[0:step:153]) > hull() > { > translate([0, 0, i]) > scale(f(i)*[1,1.19255]) > cylinder(r=161/2, h = .01); > translate([0, 0, i+step]) > scale(f(i+step)*[1,1.19255]) > cylinder(r=161/2, h = .01); > } > > function f(i) = 1+ pow(i/200,2); <http://forum.openscad.org/file/n17409/hat.png> -- View this message in context: http://forum.openscad.org/Curved-linear-extrude-tp17407p17409.html Sent from the OpenSCAD mailing list archive at Nabble.com. _______________________________________________ OpenSCAD mailing list Discuss@lists.openscad.org http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.6201 / Virus Database: 4568/12284 - Release Date: 05/23/16

Thanks Neon22 this is also a very useful approach. -----Original Message----- From: Discuss [mailto:discuss-bounces@lists.openscad.org] On Behalf Of Neon22 Sent: 24 May 2016 00:18 To: discuss@lists.openscad.org Subject: Re: [OpenSCAD] Curved linear extrude Also consider approach where you draw the profile and build a volume of revolution Check this code for example to make handles: - http://www.thingiverse.com/thing:923244 (tricky to ensure they meet perfectly in the mifddle) Use inkscape to draw the profile: - http://www.thingiverse.com/thing:1065500 -- View this message in context: http://forum.openscad.org/Curved-linear-extrude-tp17407p17410.html Sent from the OpenSCAD mailing list archive at Nabble.com. _______________________________________________ OpenSCAD mailing list Discuss@lists.openscad.org http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.6201 / Virus Database: 4568/12284 - Release Date: 05/23/16