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Merge pull request #72 from rodrigorc/master

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This PR adds a rack() module to the involute_gears() module. It is basically a
section of the rim of a gear of infinite teeth.

It has a subset or the gear() arguments:

 - number_of_teeth: will affect the length of the rack.
   circular_pitch or diametral_pitch: must match that of the gear.
 - pressure_angle: must match that of the gear.
 - rim_thickness: there is no disk or hub so this is the only thickness.
 - rim_width: width of the flat ribbon behind the teeth.
 - clearance
 - flat

The other ones do not make much sense for a rack.

A rack and a gear will match if they have the same pitch and pressure angle. The
origin point or a rack is set to the middle point of the "pitch line", so to
align it with a gear, just move it to the pitch circle of the gear.

I've added a small rack to the test_gears() module, but feel free to change of
remove it if it is not appropriate.
This commit is contained in:
Chow Loong Jin 2020-03-29 23:14:38 +08:00
parent 8b0a49d467 f6f4fd5d8d
commit 9fd97fa52d
1 changed files with 46 additions and 0 deletions
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46
involute_gears.scad
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@ -396,6 +396,46 @@ module gear (
}
}
module rack(
number_of_teeth=15,
circular_pitch=false, diametral_pitch=false,
pressure_angle=28,
clearance=0.2,
rim_thickness=8,
rim_width=5,
flat=false)
{
if (circular_pitch==false && diametral_pitch==false)
echo("MCAD ERROR: gear module needs either a diametral_pitch or circular_pitch");
//Convert diametrial pitch to our native circular pitch
circular_pitch = (circular_pitch!=false?circular_pitch:180/diametral_pitch);
pitch = circular_pitch / 180 * PI;
addendum = circular_pitch / 180;
dedendum = addendum + clearance;
pitch_slope = tan(pressure_angle);
linear_extrude_flat_option(flat=flat, height=rim_thickness)
union()
{
translate([0,-dedendum-rim_width/2])
square([number_of_teeth*pitch, rim_width],center=true);
p1 = pitch / 4 + pitch_slope * dedendum;
p2 = pitch / 4 - pitch_slope * addendum;
for(i=[1:number_of_teeth])
translate([pitch*(i-number_of_teeth/2-0.5),0])
polygon(points=[
[-p1,-dedendum],
[p1,-dedendum],
[p2,addendum],
[-p2,addendum]
]);
}
}
module linear_extrude_flat_option(flat =false, height = 10, center = false, convexity = 2, twist = 0)
{
if(flat==false)
@ -555,6 +595,12 @@ module test_gears()
circles=5,
hub_diameter=2*8.88888889);
translate ([-37.5,0,0])
rotate ([0,0,-90])
rack (
circular_pitch=500
);
translate ([0,0,10])
{
gear (