I created a curve using linear_extrude of a circle, with the twist
parameter
and the resulting extrusion twists around an invisible cylinder. What I am
looking to do is have the extrusion twist around an elliptical cylinder. I
could scale after the linear_extrude, and while that does make the hole
elliptical, it also stretches the extrusions, which I do not want.

As you can see here, the left shape extrudes around a cylinder - on the
right after using scale the hole becomes elliptical cylinder but the
extrusions are stretched as well.

http://forum.openscad.org/file/n17868/Capture.png

What is the best way to accomplish this?

--
View this message in context:
http://forum.openscad.org/Can-linear-extrude-twist-elliptically-instead-of-circularly-tp17868.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

a = 3;
b = 2;
scale([a,b,1]) linear_extrude(40, twist=360) translate([2*a,0])
scale([1/a,1/b]) circle(5);

That doesn't seem to work. Try changing a = 4 and b = 1:

a = 4;
b = 1;
scale([a,b,1]) linear_extrude(40, twist=360) translate([2*a,0])
scale([1/a,1/b]) circle(5);

http://forum.openscad.org/file/n17885/Capture.png

The extrusion is not circular.

--
View this message in context:
http://forum.openscad.org/Can-linear-extrude-twist-elliptically-instead-of-circularly-tp17868p17885.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

I created a curve using linear_extrude of a circle, with the twist
parameter
and the resulting extrusion twists around an invisible cylinder. What I am
looking to do is have the extrusion twist around an elliptical cylinder. I
could scale after the linear_extrude, and while that does make the hole
elliptical, it also stretches the extrusions, which I do not want.

As you can see here, the left shape extrudes around a cylinder - on the
right after using scale the hole becomes elliptical cylinder but the
extrusions are stretched as well.

http://forum.openscad.org/file/n17868/Capture.png

What is the best way to accomplish this?

--
View this message in context:
http://forum.openscad.org/Can-linear-extrude-twist-elliptically-instead-of-circularly-tp17868.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

From the beginning, you were asking for a translational sweeping. Here you

translational_sweep(elliptical_path(40,10,40,360,$fa=5)) circle(5);

module translational_sweep(path) {
dz = h/(len(path)-1);
for(i=[0:len(path)-2]){
hull(){
translate(path[i])
linear_extrude(0.001) children();
translate(path[i+1])
linear_extrude(0.001) children();
}
}
}

function elliptical_path(a,b,h,ang) =
[ for(x=[0:$fa:ang]) [acos(x), bsin(x), h*x/ang] ];

translational_sweep2(path(), closed=true) star();

module translational_sweep2(path, closed=false) {
p = closed ? concat( path, [ path[0] ]) : path;
for(i=[0:len(p)-2]){
if( p[i+1][2]-p[i][2] > 0 ) {
translate(p[i])
slice(p[i], p[i+1]) children();
}
else if( p[i+1][2]-p[i][2] < 0 ) {
translate(p[i+1])
slice(p[i+1], p[i]) children();
}
else {
minkowski(){
linear_extrude(0.0001) children();
hull() {
translate(p[i]) cube(0.0001);
translate(p[i+1]) cube(0.0001);
}
}
}
}
}

function path() =
concat([ for(x=[0:5:180]) [40cos(x), 40sin(x), 100x/360] ],
[ for(x=[180:-5:0]) [-40cos(x), -40sin(x), 100x/360] ] ) ;

module star() {
scale([3,1]) rotate(45) square(5,center=true);
scale([1,3]) rotate(45) square(5,center=true); }

module slice(a,b) {
multmatrix(shear([(b[0]-a[0])/(b[2]-a[2]), (b[1]-a[1])/(b[2]-a[2])]))
linear_extrude(b[2]-a[2]) children();
}

function shear(d=[0,0])=
[ [1,0,d[0],0], [0,1,d[1],0],[0,0,1,0],[0,0,0,1] ];