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224 lines
9.9 KiB
OpenSCAD
224 lines
9.9 KiB
OpenSCAD
//
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// NopSCADlib Copyright Chris Palmer 2019
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// nop.head@gmail.com
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// hydraraptor.blogspot.com
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//
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// This file is part of NopSCADlib.
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//
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// NopSCADlib is free software: you can redistribute it and/or modify it under the terms of the
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// GNU General Public License as published by the Free Software Foundation, either version 3 of
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// the License, or (at your option) any later version.
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//
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// NopSCADlib is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
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// without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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// See the GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License along with NopSCADlib.
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// If not, see <https://www.gnu.org/licenses/>.
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//
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//
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//! Utilities for making threads with sweep. They can be used to model screws, nuts, studding, leadscrews, etc, and also to make printed threads.
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//!
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//! The ends can be tapered, flat or chamfered by setting the ```top``` and ```bot``` parameters to -1 for tapered, 0 for a flat cut and positive to
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//! specify a chamfer angle.
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//!
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//! Threads are by default solid, so the male version is wrapped around a cylinder and the female inside a tube. This can be suppressed to just get the helix, for
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//! example to make a printed pot with a screw top lid.
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//!
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//! A left hand thread can be made by using mirror([0,1]).
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//!
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//! Threads with a typical 60 degree angle appear too bright with OpenSCAD's primitive lighting model as they face towards the lights more than the top and sides of
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//! a cylinder. To get around this a colour can be passed to thread that is used to colour the cylinder and then toned down to colour the helix.
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//!
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//! Making the ends requires a CGAL intersection, which make threads relatively slow. For this reason they are generally disabled when using the GUI but can
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//! be enabled by setting ```$show_threads``` to ```true```. When the tests are run, by default, threads are enabled only for things that feature them like screws.
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//! This behaviour can be changed by setting a ```NOPSCADLIB_SHOW_THREADS``` environment variable to ```false``` to disable all threads and ```true``` to enable all threads.
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//! The same variable also affects the generation of assembly diagrams.
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//!
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//! Threads obey the $fn, $fa, $fs variables.
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//
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include <../utils/core/core.scad>
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use <sweep.scad>
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use <maths.scad>
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use <tube.scad>
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thread_colour_factor = 0.8; // 60 degree threads appear too bright due to the angle facing the light sources
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function thread_profile(h, crest, angle, overlap = 0.1) = //! Create thread profile path
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let(base = crest + 2 * (h + overlap) * tan(angle / 2))
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[[-base / 2, -overlap, 0], [-crest / 2, h, 0], [crest / 2, h, 0], [base / 2, -overlap, 0]];
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module thread(dia, pitch, length, profile, center = true, top = -1, bot = -1, starts = 1, solid = true, female = false, colour = undef) { //! Create male or female thread, ends can be tapered, chamfered or square
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//
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// Apply colour if defined
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//
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module colour(factor) if(is_undef(colour)) children(); else color(colour * factor) children();
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//
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// Compress the profile to compensate for it being tilted by the helix angle
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//
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scale = cos(atan(pitch / (PI * dia)));
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sprofile = [for(p = profile) [p.x * scale, p.y, p.z]];
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//
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// Extract some properties from the profile, perhaps they should be stored in it.
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//
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h = max([for(p = sprofile) p.y]);
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xs = [for(p = sprofile) p.x];
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maxx = max(xs);
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minx = min(xs);
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crest_xs = [for(p = sprofile) if(p.y == h) p.x];
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crest_xmax = max(crest_xs);
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crest_xmin = min(crest_xs);
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//
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// If the ends don't taper we need an extra half turn past the ends to be cropped horizontally.
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//
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extra_top = top < 0 ? 0 : -minx / pitch;
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extra_bot = bot < 0 ? 0 : maxx / pitch;
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turns = length / pitch + extra_top + extra_bot;
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//
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// Generate the helix path, possibly with tapered ends
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//
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dir = female ? 1 : -1;
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r = dia / 2;
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sides = r2sides4n(r);
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step_angle = 360 / sides;
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segs = ceil(turns * sides);
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leadin = min(ceil(sides / starts), floor(turns * sides / 2));
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final = floor(turns * sides) - leadin;
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path = [for(i = [0 : segs],
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R = i < leadin && bot < 0 ? r + dir * (h - h * i / leadin)
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: i > final && top < 0 ? r + dir * h * (i - final) / leadin : r,
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a = i * step_angle - 360 * extra_bot)
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[R * cos(a), R * sin(a), a * pitch / 360]];
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//
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// Generate the skin vertices
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//
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facets = len(profile);
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twist = helical_twist_per_segment(r, pitch, sides);
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//
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// For female threads we need to invert the profile
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//
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iprofile = female ? reverse([for(p = sprofile) [p.x, -p.y, 0]]) : sprofile;
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//
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// If the bottom is tapered then the twist will be greater, so pre-twist the profile to get the straight bit at the correct angle
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//
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rprofile = bot < 0 ? transform_points(iprofile, rotate(-dir * (helical_twist_per_segment(r - h, pitch, sides) - twist) * sides / PI))
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: iprofile;
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points = skin_points(rprofile, path, false, twist * segs);
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//
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// To form the ends correctly we need to use intersection but it is very slow with the full thread so we just
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// intersect the start and the end and sweep the rest outside of the intersection.
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//
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top_chamfer_h = (top > 0 ? h * tan(top) : 0);
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bot_chamfer_h = (bot > 0 ? h * tan(bot) : 0);
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top_overlap = max( maxx, top_chamfer_h - crest_xmin) / pitch;
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bot_overlap = max(-minx, bot_chamfer_h + crest_xmax) / pitch;
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start = ceil(sides * (bot_overlap + extra_bot));
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end = segs - ceil(sides * (top_overlap + extra_top));
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start_skin_faces = skin_faces(points, start + 1, facets, false);
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middle_skin_faces = skin_faces(points, end - start + 1, facets, false, start);
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end_skin_faces = skin_faces(points, segs - end + 1, facets, false, end);
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start_faces = concat([cap(facets) ], start_skin_faces, [cap(facets, start)]);
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middle_faces = concat([cap(facets, start, false)], middle_skin_faces, [cap(facets, end)]);
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end_faces = concat([cap(facets, end, false)], end_skin_faces, [cap(facets, segs)]);
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overlap = - profile[0].y;
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translate_z((center ? -length / 2 : 0)) {
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ends_faces = concat(start_faces, end_faces);
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for(i = [0 : starts - 1])
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colour(thread_colour_factor)
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rotate(360 * i / starts + (female ? 180 / starts : 0)) {
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render() intersection() {
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polyhedron(points, ends_faces);
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shorten = !is_undef(colour);
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len = shorten ? length - 2 * eps : length;
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offset = shorten ? eps : 0;
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rotate_extrude()
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if(female) {
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difference() {
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translate([0, offset])
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square([r + h + overlap, len]);
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if(top_chamfer_h)
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polygon([[0, length], [r, length], [r - h, length - top_chamfer_h], [0, length - top_chamfer_h]]);
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if(bot_chamfer_h)
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polygon([[0, 0], [r, 0], [r - h, bot_chamfer_h], [0, bot_chamfer_h]]);
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}
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}
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else
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difference() {
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hull() {
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translate([0, offset])
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square([r, len]);
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translate([0, bot_chamfer_h])
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square([r + h + overlap, len - top_chamfer_h - bot_chamfer_h]);
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}
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if(!solid)
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square([r - overlap, length]);
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}
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}
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polyhedron(points, middle_faces);
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}
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if(solid)
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colour(1)
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rotate(90)
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if(female)
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tube(or = r + (top < 0 || bot < 0 ? h : 0) + 2 * overlap, ir = r, h = length, center = false);
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else
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cylinder(d = dia, h = length);
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}
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}
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module male_metric_thread(d, pitch, length, center = true, top = -1, bot = -1, solid = true, colour = undef) { //! Create male thread with metric profile
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H = pitch * sqrt(3) / 2;
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h = 5 * H / 8;
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minor_d = d - 2 * h;
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thread(minor_d, pitch, length, thread_profile(h, pitch / 8, 60), center, top, bot, solid = solid, colour = colour);
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}
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module female_metric_thread(d, pitch, length, center = true, top = -1, bot = -1, colour = undef) { //! Create female thread with metric profile
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H = pitch * sqrt(3) / 2;
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h = 5 * H / 8;
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thread(d, pitch, length, thread_profile(h, pitch / 4, 60), center, top, bot, solid = false, female = true, colour = colour);
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}
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function metric_coarse_pitch(d) //! Convert metric diameter to pitch
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= d == 1.6 ? 0.35 // M1.6
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: [0.4, // M2
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0.45,// M2.5
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0.5, // M3
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0.6, // M3.5
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0.7, // M4
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0,
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0.8, // M5
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0,
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1.0, // M6
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0,
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0,
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0,
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1.25, // M8
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0,
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0,
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0,
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1.5, // M10
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0,
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0,
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0,
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1.75, // M12
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0,
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0,
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0,
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0, // M14
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0,
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0,
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0,
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2.0, // M16
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][d * 2 - 4];
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