I found these a while ago - and I use them quite frequently, I'm afraid they were examples found in a trawl so I am unable to provide credit to the originator [sorry :-(] The first two modules provide the core elements, the third is an example of usage. There is a problem with the intersections, which is the purpose of adding and subtracting 3 module arc(radius, angles, width = 1, fn = 100) {   angles = [angles[0]+3,angles[1]-3];   echo (angles[0]);   difference() {         sector(radius + width, angles, fn);         sector(radius, angles, fn);     } } module sector(radius, angles, fn = 100) {     echo ("sector from apex modules");     r = radius / cos(180 / fn);     step = -360 / fn;     points = concat([[0, 0]],         [for(a = [angles[0] : step : angles[1] - 360])             [r * cos(a), r * sin(a)]         ],         [[r * cos(angles[1]), r * sin(angles[1])]]     );     difference() {         circle(radius, $fn = fn);         polygon(points);     } }// end module sector module rounded_end_slot_arc (arc_radius=10,arc_width=4,arc_z=10,start_angle=0,end_angle=20,local_roundness=60) { slot_width = arc_width; slot_rad = arc_radius; slot_angles = [start_angle,end_angle]; slot_z = arc_z; arc_rad = slot_rad - slot_width/2;   //  rotate ([0,0,slot_angles[0]+3])     //    translate ([slot_rad,0,-0.1])       //      cylinder (d=slot_width,h=slot_z,$fn=local_roundness); //    rotate ([0,0,slot_angles[1]-3])   //      translate ([slot_rad,0,-0.1])     //        cylinder (d=slot_width,h=slot_z,$fn=local_roundness);     translate ([0,0,-0.1])         linear_extrude (slot_z)             arc(arc_rad,slot_angles, slot_width, $fn=100); }// end module rounded_end_slot_arc (15,4,6,0,20,60); If you uncomment the cylinders from the above example you get a round end object you can cut a slot with.   By changing the arc radius and the width you can achieve a pie slice of any height you need, no differences required. HTH Roger