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207 lines
7.0 KiB
OpenSCAD
207 lines
7.0 KiB
OpenSCAD
/*
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* Modified by the DoomMeister
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* To allow a parsable quality setting, better tuned for BSP threads
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*
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* Origionally By
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* Dan Kirshner - dan_kirshner@yahoo.com
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*
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* You are welcome to make free use of this software. Retention of my
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* authorship credit would be appreciated.
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*
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* Version 1.3. 2013-12-01 Correct loop over turns -- don't have early cut-off
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* Version 1.2. 2012-09-09 Use discrete polyhedra rather than linear_extrude()
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* Version 1.1. 2012-09-07 Corrected to right-hand threads!
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*/
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// Examples:
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//metric_thread(8, 1, 10);
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//english_thread(1/4, 20, 1);
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// Rohloff hub thread:
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//metric_thread(34, 1, 10, internal=true, n_starts=6);
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//metric_thread(8, 2, 4);
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thread_polyhedron(1.309*0.5*25.4, 1/11*25.4, false, 1,20);
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// ----------------------------------------------------------------------------
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pi = 3.14159265;
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// ----------------------------------------------------------------------------
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function segments(diameter) = min(10, ceil(diameter*6));
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// ----------------------------------------------------------------------------
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// internal - true = clearances for internal thread (e.g., a nut).
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// false = clearances for external thread (e.g., a bolt).
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// (Internal threads should be "cut out" from a solid using
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// difference()).
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// n_starts - Number of thread starts (e.g., DNA, a "double helix," has
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// n_starts=2). See wikipedia Screw_thread.
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module metric_thread(diameter=8, pitch=1, length=1, internal=false, n_starts=1,tq=10)
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{
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// Number of turns needed.
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n_turns = floor(length/pitch);
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n_segments = tq;
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h = pitch * cos(27.5);
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union() {
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intersection() {
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// Start one below z = 0. Gives an extra turn at each end.
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for (i=[-1*n_starts : n_turns+1]) {
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translate([0, 0, i*pitch]) {
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metric_thread_turn(diameter, pitch, internal, n_starts,tq);
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}
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}
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// Cut to length.
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translate([0, 0, length/2]) {
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cube([diameter*1.1, diameter*1.1, length], center=true);
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}
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}
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// Solid center, including Dmin truncation.
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if (internal) {
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cylinder(r=diameter/2 - h*5/8, h=length, $fn=n_segments);
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} else {
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// External thread includes additional relief.
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cylinder(r=diameter/2 - h*5.3/8, h=length, $fn=n_segments);
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}
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}
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}
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// ----------------------------------------------------------------------------
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// Input units in inches.
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// Note: units of measure in drawing are mm!
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module english_thread(diameter=0.25, threads_per_inch=20, length=1,
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internal=false, n_starts=1,tq=10)
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{
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// Convert to mm.
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mm_diameter = diameter*25.4;
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mm_pitch = (1.0/threads_per_inch)*25.4;
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mm_length = length*25.4;
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echo(str("mm_diameter: ", mm_diameter));
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echo(str("mm_pitch: ", mm_pitch));
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echo(str("mm_length: ", mm_length));
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metric_thread(mm_diameter, mm_pitch, mm_length, internal, n_starts,tq);
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}
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// ----------------------------------------------------------------------------
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module metric_thread_turn(diameter, pitch, internal, n_starts,tq)
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{
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n_segments = tq;
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fraction_circle = 1.0/n_segments;
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for (i=[0 : n_segments-1]) {
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rotate([0, 0, i*360*fraction_circle]) {
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translate([0, 0, i*n_starts*pitch*fraction_circle]) {
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thread_polyhedron(diameter/2, pitch, internal, n_starts,tq);
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}
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}
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}
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}
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// ----------------------------------------------------------------------------
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// z (see diagram) as function of current radius.
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// (Only good for first half-pitch.)
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function z_fct(current_radius, radius, pitch)
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= 0.5*(current_radius - (radius - 0.875*pitch*cos(30)))
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/cos(30);
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// ----------------------------------------------------------------------------
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module thread_polyhedron(radius, pitch, internal, n_starts,tq)
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{
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n_segments = tq;
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fraction_circle = 1.0/n_segments;
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h = pitch * cos(30);
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outer_r = radius + (internal ? h/20 : 0); // Adds internal relief.
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//echo(str("outer_r: ", outer_r));
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inner_r = radius - 0.875*h; // Does NOT do Dmin_truncation - do later with
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// cylinder.
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// Make these just slightly bigger (keep in proportion) so polyhedra will
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// overlap.
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x_incr_outer = outer_r * fraction_circle * 2 * pi * 1.005;
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x_incr_inner = inner_r * fraction_circle * 2 * pi * 1.005;
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z_incr = n_starts * pitch * fraction_circle * 1.005;
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/*
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(angles x0 and x3 inner are actually 60 deg)
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/\ (x2_inner, z2_inner) [2]
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/ \
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(x3_inner, z3_inner) / \
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[3] \ \
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|\ \ (x2_outer, z2_outer) [6]
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| \ /
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| \ /|
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z | \/ / (x1_outer, z1_outer) [5]
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| | | /
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| x | |/
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| / | / (x0_outer, z0_outer) [4]
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| / | / (behind: (x1_inner, z1_inner) [1]
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|/ | /
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y________| |/
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(r) / (x0_inner, z0_inner) [0]
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*/
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x1_outer = outer_r * fraction_circle * 2 * pi;
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z0_outer = z_fct(outer_r, radius, pitch);
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//echo(str("z0_outer: ", z0_outer));
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//polygon([[inner_r, 0], [outer_r, z0_outer],
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// [outer_r, 0.5*pitch], [inner_r, 0.5*pitch]]);
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z1_outer = z0_outer + z_incr;
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// Rule for triangle ordering: look at polyhedron from outside: points must
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// be in clockwise order.
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polyhedron(
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points = [
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[-x_incr_inner/2, -inner_r, 0], // [0]
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[x_incr_inner/2, -inner_r, z_incr], // [1]
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[x_incr_inner/2, -inner_r, pitch + z_incr], // [2]
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[-x_incr_inner/2, -inner_r, pitch], // [3]
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[-x_incr_outer/2, -outer_r, z0_outer], // [4]
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[x_incr_outer/2, -outer_r, z0_outer + z_incr], // [5]
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[x_incr_outer/2, -outer_r, pitch - z0_outer + z_incr], // [6]
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[-x_incr_outer/2, -outer_r, pitch - z0_outer] // [7]
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],
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faces = [
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[0, 3, 4], // This-side trapezoid, bottom
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[3, 7, 4], // This-side trapezoid, top
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[1, 5, 2], // Back-side trapezoid, bottom
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[2, 5, 6], // Back-side trapezoid, top
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[0, 1, 2], // Inner rectangle, bottom
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[0, 2, 3], // Inner rectangle, top
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[4, 6, 5], // Outer rectangle, bottom
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[4, 7, 6], // Outer rectangle, top
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[7, 2, 6], // Upper rectangle, bottom
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[7, 3, 2], // Upper rectangle, top
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[0, 5, 1], // Lower rectangle, bottom
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[0, 4, 5] // Lower rectangle, top
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]
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);
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}
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