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involute.py
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involute.py
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#!/usr/bin/python
import math
dp = 16 # Diametral Pitch
teeth = 30
pa = 20 # Pressure Angle
bore=2/25.4 # Center bore radius
printsvg=True
backlash=0.0 #backlash in degrees. Use positive for exterior spur gears, negative for interior
scale=250.4
def conv(inches):
return inches*25.4
pd = float(teeth/float(dp)) # Pitch Diameter
pr = pd/2 #Pitch Radius
addendum = 1.0/dp+.01
dedendum = 1.157/dp
rootradius = math.cos(pa*2*math.pi/360.0)*pr
rootcircum=2*math.pi*rootradius
roottan = math.sin(pa*2*math.pi/360.0)*pr
rootangle = pa - 360*roottan/rootcircum
size= 2.2*(pr+addendum)*scale
offset=size/2
def calcpoint(rad,theta=0):
global offset
global scale
angle,radius=rad
angle=angle+theta
return scale*radius*math.cos(angle*math.pi/180.0)+offset,scale*radius*math.sin(angle*math.pi/180.0)+offset
if (pr-dedendum) > rootradius:
start=pr-dedendum
else:
start=rootradius
delta= (pr+addendum-start)/float(30)
points=[]
points2=[]
for x in range(0,31):
tanlength=math.sqrt( (start+x*delta)**2 - rootradius**2)
tanangle = rootangle+360*tanlength/rootcircum - 180*math.atan(tanlength/rootradius)/math.pi
tanangle2 = rootangle-360*tanlength/rootcircum + 180*math.atan(tanlength/rootradius)/math.pi
points.append((tanangle,start+x*delta))
points2.append((tanangle2-2*rootangle-backlash+360/(teeth*2.0),start+x*delta))
if printsvg:
print '<?xml version="1.0"?> <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">'
print '<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="%f" height="%f" >'%(size,size)
#print '<circle cx="%f" cy="%f" r="%f" stroke="red" stroke-width="1" fill="none" />'%(offset,offset,pr*scale)
#print '<circle cx="%f" cy="%f" r="%f" stroke="green" stroke-width="1" fill="none" />'%(offset,offset,rootradius*scale)
print '<circle cx="%f" cy="%f" r="%f" stroke="black" stroke-width="1" fill="none" />'%(offset,offset,(bore)*scale)
theta=360/float(teeth)
for i in range(0,teeth):
print '<path d="M %f,%f C '%calcpoint(points[0],i*theta),
for p in points[1:]:
print "%f, %f "%calcpoint(p,i*theta),
print '" fill="none" stroke="#000000" stroke-width="1" />'
print '<path d="M %f,%f C '%calcpoint(points2[0],i*theta),
for p in points2[1:]:
print "%f, %f "%calcpoint(p,i*theta),
print '" fill="none" stroke="#000000" stroke-width="1" />'
print '<path d="M%f,%f'%calcpoint(points[-1],i*theta),
print 'A %f %f '%((pr+addendum)*scale,(pr+addendum)*scale),
print '0 0 1 %f %f" fill="none" stroke="#000000" stroke-width="1" />'%calcpoint(points2[-1],i*theta)
dr=pr-dedendum #dedendum radius
dedendumpoint1=(points[0][0],dr)
dedendumpoint2=(points2[0][0],dr)
for i in range(0,teeth):
print '<path d="M%f,%f'%calcpoint(dedendumpoint1,(i+1)*theta),
print 'A %f %f '%((dr)*scale,(dr)*scale),
print '0 0 1 %f %f" fill="none" stroke="#000000" stroke-width="1" />'%calcpoint(dedendumpoint2,i*theta)
print '<line x1="%f" y1="%f" x2="%f" y2="%f" '%(calcpoint(dedendumpoint1,i*theta)+calcpoint(points[0],i*theta))
print 'style="stroke:#000000;stroke-width:1" />'
print '<line x1="%f" y1="%f" x2="%f" y2="%f" '%(calcpoint(dedendumpoint2,i*theta)+calcpoint(points2[0],i*theta))
print 'style="stroke:#000000;stroke-width:1" />'
print "</svg>"
else:
print pr