@Sanjeev - thanks for running an eye over my code, whilst 3D geometry is something I can generally figure out, the mathematical side has always been er, 'a challenge', its not how my brain works :-(.  I took a look at your github PDF, it looks so simple when you explain it like that... Here is another bit of code I have been developing - it was inspired by a 3d model I found [somewhere] for a circular box which fits a pringles can lid.  As is not unusual for Thingiverse [or wherever, models], it was a bit off and lacked a chamfer on the outside edge to make fitting the lid easier. So here's my implementation..  uses the same computation for generating a set of points for a rounded internal corner so I can get small components out. Change the diameter and you can make circular boxes [trays?] which fit any lid from a mini ice cream tub [Haagan Dazs, size = 67], through coffee tins etc. etc. The comment on line 42 [where else?]  with example 1, will also make a hexagonal box with a brim which looks user friendly.  It would be an exercise to replace the top with the code at example 4, thus making a rounded edge to the container A discussion that came up recently. // Generate list of points in Console for copying to bezier_cam_paths_v1.scad.  X,Y then edited to include Z coordinate for bezier curve // see https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/List_Comprehensions $fa = 2; $fs = 1; echo (p1); outside_od = 78;//pringles outside_r = 78/2; inner_radius = 2; wall_thick = 1; //inside_rad = 37;//37 chamfer = 0.3; //wall_z of 10 is OK for testing, but too small to be useful as the lid overlaps by about half the depth so its harder to remove. wall_z = 10;//[10:5:30] lip_thick = 1.8; lip_height = 1.; inside_rad = outside_r - lip_thick; inner_r_offset = inside_rad - inner_radius; outside_rad = inside_rad + wall_thick; origin_p = [0,0]; p1 = [[0,0], [0,wall_thick], for (chi = [270 : 5 : 360]) [(inner_radius * cos(chi))+ inner_r_offset , inner_radius * sin(chi)+inner_radius + wall_thick], [inside_rad,wall_z-chamfer], [inside_rad+chamfer,wall_z], [inside_rad+lip_thick-chamfer,wall_z], [inside_rad+lip_thick,wall_z-chamfer], [inside_rad+lip_thick,wall_z-chamfer-lip_height], [outside_rad+chamfer,wall_z-chamfer*3-lip_height], [outside_rad+chamfer,chamfer], [outside_rad,0], ]; //Example 1, set $fn to 4 for a square or six for a hex, or remove altogether for a circle...  Coincidentally [not] the diameter of 78 makes a circular box which fits a pringle lid //rotate_extrude ($fn=4) //polygon (p1); //Example 2 //polygon (quarter_circle_p(18,0,30)); steps = 50; points = [     // first expression generating the points in the positive Y quadrant     for (a = [0 : steps]) [ a, 10 * sin(a * 360 / steps) + 10 ],     // second expression generating the points in the negative Y quadrant     for (a = [steps : -1 : 0]) [ a, 10 * cos(a * 360 / steps) - 20 ],     // additional list of fixed points     [ 10, -3 ], [ 3, 0 ], [ 10, 3 ] ]; //Example 3 //polygon(points); function circle(radius) = [for (phi = [60 : 10 : 300]) [radius * cos(phi), radius * sin(phi)]]; //polygon(circle(64)); //echo(circle(64)); function half_circle (radius) = [for (chi = [0 : 10 : 180])     [radius * cos(chi), radius * sin(chi)]]; //Example 4 translate ([60,0,0]) polygon (half_circle(2)); //example 5, add fn=6 and its a hexagonal half circle. //rotate_extrude() translate ([60,0,0]) polygon (half_circle(2)); function quarter_circle (radius) = [for (chi = [270 : 5 : 360])     [radius * cos(chi), radius * sin(chi)]]; //translate ([0,0,40]) polygon (quarter_circle(8)); function quarter_circle_p (radius,start_angle,end_angle) = [for (chi = [start_angle : 5 : end_angle])     [radius * cos(chi), radius * sin(chi)]];