Class: CrystalScad::PrintedThreads::PrintedThread

Inherits:
Object
  • Object
show all
Defined in:
lib/crystalscad/PrintedThreads.rb

Overview

Ported from dkprojects.net/openscad-threads/threads.scad

original Author Dan Kirshner - [email protected]

Instance Method Summary collapse

Constructor Details

#initialize(args = {}) ⇒ PrintedThread

internal - true = clearances for internal thread (e.g., a nut).

false = clearances for external thread (e.g., a bolt).
(Internal threads should be "cut out" from a solid using
difference()).

number_of_starts - Number of thread starts (e.g., DNA, a “double helix,” has

n_starts=2).  See wikipedia Screw_thread.



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# File 'lib/crystalscad/PrintedThreads.rb', line 16

def initialize(args={})
  @args = args
  @args[:diameter] ||= 8
  @args[:pitch] ||= 1.25
  @args[:length] ||=10
  @args[:internal] ||= false
  @args[:number_of_starts] ||= 1
end

Instance Method Details

#metric_thread_turn(diameter, pitch, internal, number_of_starts) ⇒ Object 



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# File 'lib/crystalscad/PrintedThreads.rb', line 56

def metric_thread_turn(diameter, pitch, internal, number_of_starts)
  number_of_segments = segments(diameter)
    fraction_circle = 1.0/number_of_segments
  res = nil

  (0..number_of_segments-1).each do |i|
    res += thread_polyhedron(diameter/2.0, pitch, internal, number_of_starts).translate(z:i*number_of_starts*pitch*fraction_circle).rotate(z:i*360*fraction_circle)
  end
  res

end

#output ⇒ Object 



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# File 'lib/crystalscad/PrintedThreads.rb', line 29

def output
  number_of_turns = (@args[:length].to_f/@args[:pitch].to_f).floor
  number_of_segments = segments(@args[:diameter])
  h = @args[:pitch] * Math::cos(radians(30)) 
    
  res  = nil
  ((-1*@args[:number_of_starts])..(number_of_turns+1)).each do |i|
    res += metric_thread_turn(@args[:diameter], @args[:pitch], @args[:internal], @args[:number_of_starts]).translate(z:i*@args[:pitch])
  end
  # cut to length
  res *= cube(x:@args[:diameter]*1.1, y:@args[:diameter]*1.1, z:@args[:length]).center.translate(z:@args[:length]/2.0)
  
  if @args[:internal]
    # Solid center, including Dmin truncation.
    res += cylinder(r:@args[:diameter]/2.0 - h*5.0/8.0, h:@args[:length], segments:number_of_segments)
  else
    # External thread includes additional relief.
    res += cylinder(r:@args[:diameter]/2.0 - h*5.3/8.0, h:@args[:length], segments:number_of_segments)      
  end      
  
  res      
end

#segments(diameter) ⇒ Object 



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# File 'lib/crystalscad/PrintedThreads.rb', line 52

def segments(diameter)
  [50, (diameter*6).ceil].min
end

#show ⇒ Object 



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# File 'lib/crystalscad/PrintedThreads.rb', line 25

def show
  output
end

#thread_polyhedron(radius, pitch, internal, n_starts) ⇒ Object

(angles x0 and x3 inner are actually 60 deg)

/\ (x2_inner, z2_inner) [2] / \ (x3_inner, z3_inner) / \ [3] \ \ |\ \ (x2_outer, z2_outer) [6] | \ / | \ /| z | / / (x1_outer, z1_outer) [5] | | | / | x | |/ | / | / (x0_outer, z0_outer) [4] | / | / (behind: (x1_inner, z1_inner) [1] |/ | / y__| |/ ® / (x0_inner, z0_inner) [0]



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# File 'lib/crystalscad/PrintedThreads.rb', line 94

def thread_polyhedron(radius, pitch, internal, n_starts)
  n_segments = segments(radius*2)
  fraction_circle = 1.0/n_segments

  h = pitch * Math::cos(radians(30))
  outer_r = radius + (internal ? h/20 : 0) # Adds internal relief.
   
  inner_r = radius - 0.875*h #  Does NOT do Dmin_truncation - do later with cylinder.

  # Make these just slightly bigger (keep in proportion) so polyhedra will overlap.
  x_incr_outer = outer_r * fraction_circle * 2 * Math::PI * 1.005
  x_incr_inner = inner_r * fraction_circle * 2 * Math::PI * 1.005
  z_incr = n_starts * pitch * fraction_circle * 1.005
  
  x1_outer = outer_r * fraction_circle * 2 * Math::PI

  z0_outer = z_fct(outer_r, radius, pitch);
  z1_outer = z0_outer + z_incr;
    # Rule for triangle ordering: look at polyhedron from outside: points must
    # be in clockwise order.
  
    points = [
              [-x_incr_inner/2, -inner_r, 0],                                    # [0]
              [x_incr_inner/2, -inner_r, z_incr],                    # [1]
              [x_incr_inner/2, -inner_r, pitch + z_incr],            # [2]
              [-x_incr_inner/2, -inner_r, pitch],                                # [3]

              [-x_incr_outer/2, -outer_r, z0_outer],                             # [4]
              [x_incr_outer/2, -outer_r, z0_outer + z_incr],         # [5]
              [x_incr_outer/2, -outer_r, pitch - z0_outer + z_incr], # [6]
              [-x_incr_outer/2, -outer_r, pitch - z0_outer]                      # [7]
             ]

    triangles = [
              [0, 3, 4],  # This-side trapezoid, bottom
              [3, 7, 4],  # This-side trapezoid, top

              [1, 5, 2],  # Back-side trapezoid, bottom
              [2, 5, 6],  # Back-side trapezoid, top

              [0, 1, 2],  # Inner rectangle, bottom
              [0, 2, 3],  # Inner rectangle, top

              [4, 6, 5],  # Outer rectangle, bottom
              [4, 7, 6],  # Outer rectangle, top

              [7, 2, 6],  # Upper rectangle, bottom
              [7, 3, 2],  # Upper rectangle, top

              [0, 5, 1],  # Lower rectangle, bottom
              [0, 4, 5]   # Lower rectangle, top
             ]

  return polyhedron(points:points, triangles:triangles)
end

#z_fct(current_radius, radius, pitch) ⇒ Object

z (see diagram) as function of current radius. (Only good for first half-pitch.)



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# File 'lib/crystalscad/PrintedThreads.rb', line 70

def z_fct(current_radius, radius, pitch)
  0.5*(current_radius - (radius - 0.875*pitch*Math::cos(radians(30))))/Math::cos(radians(30))      
end