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// Metric Screw Thread Library
// by Maximilian Karl <karlma@in.tum.de> (2014)
// modified the api to create internal threads, smooth the start and
// stop threads, and use imperial units:
//
//
//
// use module thread_imperial(pitch, majorD, stepAngle, numRotations, tol, internal)
// or thread(pitch, majorD, stepAngle, numRotations, tol, internal)
// with the parameters:
// pitch - screw thread pitch
// majorD - screw thread major diameter
// step - step size in degrees (36 gives ten steps per rotation)
// numRotations - the number of full rotations of the thread
// tol - (optional parameter for internal threads) the amount to increase the
// thread size in mm.Default is 0
// internal - (optional parameter for internal threads) - this can be set true or
// false. Default is true
root3 = sqrt(3);
root3div3 = root3/3;
//-----------------------------------------------------------------------------------------------
//EXAMPLES:
//example: this creates a 3/8-inch 16TPI bolt using metric units
thread(1.5875,9.5250,12,12);
//the same thread using imperial units
//thread_imperial(1/16,3/8,12,12);
//an internal thread that will accomodate the two examples above
translate([15,0,0]){
difference(){
cylinder(r=8,h=8);
translate([0,0,-1.5875/2]){thread(1.5875,9.5250,12,8, 0.2, true);}
}}
//------------------------------------------------------------------------------------------------
//Creates a thread cross section starting with an equilateral triangle
//and removing the point. Internal threads (for creating nuts) will
//have a non-zero tolerance value which enlarges the triangle to
//accomodate a bolt of the same size
module screwthread_triangle(P, tol) {
cylinderRadius=root3div3*(P+2*tol);
translate([2*tol,0,0]){
difference() {
translate([-cylinderRadius+root3/2*(P)/8,0,0])
rotate([90,0,0])
cylinder(r=cylinderRadius,h=0.00001,$fn=3,center=true);
translate([-tol,-P/2,-P/2]){
cube([P,P,P]);
}
translate([-P,-P/2,P/2]){
cube([P,P,P]);
}
translate([-P,-P/2,-3*P/2]){
cube([P,P,P]);
}
}
}
}
//Hulls two consecutive thread triangles to create a segment of the thread
module threadSegment(P,D_maj, step, tol){
for(i=[0:step:360-step]){
hull()
for(j = [0,step])
rotate([0,0,(i+j)])
translate([D_maj/2,0,(i+j)/360*P])
screwthread_triangle(P, tol);
}
}
//Places enough thread segments to create one full rotation. The first
//and last portion of external threads (for making bolts) are tapered
//at a 20 degree angle for an easier fit
module screwthread_onerotation(P,D_maj,step, tol=0, first=false, last=false, internal=false) {
H = root3/2*P;
D_min = D_maj - 5*root3/8*P;
if(internal==false){
difference(){
threadSegment(P,D_maj, step, 0);
if(first==true){
//echo("first thread");
translate([D_maj/2-P/2,0,-P/2]){
rotate(-20,[0,0,1]){translate([0,-P*5,0]){cube([P,P*10,P]); }}}
}
if(last==true){
//echo("last thread");
translate([D_maj/2-P/2,0,-P/2+P]){
rotate(20,[0,0,1]){translate([0,-P*5,0]){cube([P,P*10,P]); }}}
}
}
}else{
threadSegment(P,D_maj+tol, step, tol);
}
//make the cylinder a little larger if this is to be an internal thread
if(internal==false){
translate([0,0,P/2])
cylinder(r=D_min/2,h=2*P,$fn=360/step,center=true);
}else{
translate([0,0,P/2])
cylinder(r=D_min/2+tol,h=2*P,$fn=360/step,center=true);
}
}
//creates a thread using inches as units (tol is still in mm)
module thread_imperial(pitch, majorD, stepAngle, numRotations, tol=0, internal = false){
p=pitch*25.4;
d=majorD*25.4;
thread(p,d,stepAngle,numRotations, tol);
}
//creates a thread using mm as units
module thread(P,D,step,rotations, tol=0, internal = false) {
// added parameter "rotations"
// as proposed by user bluecamel
for(i=[0:rotations-1])
translate([0,0,i*P]){
if(i==0&&rotations<=1){
screwthread_onerotation(
P,D,step, tol, true, true, internal); //first if there is only one rotation
}else if(i==0){
screwthread_onerotation(
P,D,step, tol, true, false, internal); //first if more than one rotation
}else if(i==rotations-1){
screwthread_onerotation(
P,D,step, tol, false, true, internal); //last if more than one rotation
}else{
screwthread_onerotation(
P,D,step, tol, false, false, internal); //middle threads
}
}
}
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