Sprocket Rhinoscript

UPDATE: this script generates inaccurately spaced teeth. sorry! fixes in new version coming soon. (6.25.09)

Here’s some basic rhinoscript code to draw your own sprockets based on the number of desired teeth, chain pitch and roller diameter. It’s very basic, but enough to draw what you want and get some custom sprockets lasercut. Draw a circle that’s larger than what you think it’s going to be in top view, then run the code.

Option Explicit
'Script written by cw wang
'based on sprocket drawing instructions from http://www.gizmology.net/sprockets.htm
'Script copyrighted by cwwang.com
'Script version Sunday, March 29, 2009 7:12:48 PM

Call Main()
Sub Main()
	Dim circle:circle=Rhino.getobject("select circle",4)
	Dim teeth:teeth=Rhino.GetInteger("number of teeth",10)
	Dim pitch:pitch=RHino.GetReal("pitch",.25)
	Dim rollerD:rollerD=RHino.GetReal("roller diameter",.13)

	Dim center:center=Rhino.CircleCenterPoint(circle)	
	Dim	radius:radius=Rhino.CircleRadius(circle)
	
	Dim ln(2)
	Dim lnOff(3)
	ln(0)=Rhino.AddLine(center,array(center(0),center(1)+radius,center(2)))
	lnOff(0)=Rhino.OffsetCurve(ln(0),center,pitch/2,array(0,0,-1))(0)
	lnOff(1)=Rhino.OffsetCurve(ln(0),center,pitch/2,array(0,0,1))(0)

	
	ln(1)=Rhino.RotateObject(ln(0),center,(360/teeth),,True)
	Dim offsetDir:offsetDir=rhino.CurveEndPoint(ln(0))
	lnOff(2)=Rhino.OffsetCurve(ln(1),offsetDir,pitch/2)(0)	
	ln(2)=Rhino.RotateObject(ln(0),center,-1*(360/teeth),,True)
	lnOff(3)=Rhino.OffsetCurve(ln(2),offsetDir,pitch/2)(0)
	
	'draw rollers
	Dim intersection1:intersection1=rhino.curvecurveIntersection(lnOff(0),lnOff(3))
	Dim plane1:plane1=rhino.planeFromNormal(intersection1(0,1),array(0,0,1))
	Dim roller1:roller1= rhino.AddCircle(plane1,rollerD/2)
	Dim intersection2:intersection2=rhino.curvecurveIntersection(lnOff(1),lnOff(2))
	Dim plane2:plane2=rhino.planeFromNormal(intersection2(0,1),array(0,0,1))
	Dim roller2:roller2= rhino.AddCircle(plane2,rollerD/2)
	Dim interLn:interLn=rhino.AddLine(intersection1(0,1),intersection2(0,1))	
	
	'draw circles
	Dim rollerLineIntersection1:rollerLineIntersection1=Rhino.CurveCurveIntersection(interLn,roller1)
	Dim r1:r1=Rhino.Distance(intersection2(0,1),rollerLineIntersection1(0,1))
	Dim circle1:circle1=Rhino.addCircle(plane1,r1)
	
	Dim rollerLineIntersection2:rollerLineIntersection2=Rhino.CurveCurveIntersection(interLn,roller2)
	Dim r2:r2=Rhino.Distance(intersection2(0,1),rollerLineIntersection2(0,1))
	Dim circle2:circle2=Rhino.addCircle(plane2,r1)
	
	
	Dim tootharc(3)
	'trim sharp part
	Dim tip:tip=Rhino.CurveCurveIntersection(circle1,circle2)
	Dim arrinterval(1)
	arrInterval(0)=Rhino.CurveClosestPoint(circle1,	tip(0,1))
	arrInterval(1)=RHino.CurveClosestPoint(circle1, rollerLineIntersection1(0,1))	
	toothArc(0)=Rhino.TrimCurve(circle1,arrInterval,True)
	
	arrInterval(1)=Rhino.CurveClosestPoint(circle2,	tip(0,1))
	arrInterval(0)=RHino.CurveClosestPoint(circle2, rollerLineIntersection2(0,1))	
	toothArc(1)=Rhino.TrimCurve(circle2,arrInterval,True)
	
	'trim valley
	Dim intersection:intersection=Rhino.CurveCurveIntersection(roller1,lnOff(3))
	arrinterval(0)=Rhino.CurveClosestpoint(roller1,rollerLineIntersection1(0,1))
	arrInterval(1)=RHino.CurveClosestPoint(roller1,	 intersection(1,1))
	toothArc(2)=Rhino.TrimCurve(roller1,arrInterval,True)

	intersection=Rhino.CurveCurveIntersection(roller2,lnOff(1))
	arrinterval(1)=Rhino.CurveClosestpoint(roller2,rollerLineIntersection2(0,1))
	arrInterval(0)=RHino.CurveClosestPoint(roller2,	 intersection(1,1))
	toothArc(3)=Rhino.TrimCurve(roller2,arrInterval,True)

		
	'delete stuff
	Call Rhino.DeleteObjects(ln)
	Call Rhino.DeleteObjects(lnOff)
	Call RHino.DeleteObject(interLn)
	
	Dim sprocketCrv()
	ReDim sprocketCrv(1)
		
	sprocketCrv(0)=Rhino.JoinCurves(toothArc,True)(0)

	Dim i
	For i=1 To teeth-1
		ReDim Preserve sprocketCrv(i)
		sprocketCrv(i)= Rhino.RotateObject(sprocketCrv(0),center,i*360/teeth,,True)
	Next
	
	Call Rhino.JoinCurves(sprocketCrv,True)
	
	Call Rhino.AddText(teeth,center,pitch)
	
	Call Rhino.addPoint(center)

End Sub