It’s my day for reviving ancient threads. This one asks if there’s a tutorial for creating a helical gear in Rhino. As far as I’m aware, there still is not. Mitch above suggested a simple twist of one end of a straight-extruded gear with respect to the other would suffice. What that produces is “straight teeth set on an angle” – which is not a true screw form, as is required. Its teeth are not radially symmetric to the rotational axis. So here’s the tutorial for making a true helical gear, 2 years late.
A better way is to use this old patternmaker’s trick to create a true helical gear, inspired by Joseph Horner’s “Helical Gears: a practical treatise” of 1893. He says: “Mark straight diagonal lines, representing the tooth-points, on a strip of paper, and glue this around the face of the prepared block. The bending of the paper to the curvature of the block will develop the helical form from the straight lines.”. We can do this in Rhino very easily.
- Create your gear profile - the best is Rainer Hessmer’s Involute Spur Gear Builder, or Doug Roger’s standalone app based on the Hessmer algorithm, GearBakery.
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Extrude over this a cylinder equal to the OD of the gear wheel.
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Use “UnrollSrf” command on the cylinder to make the “strip of paper”, which will presently be wrapped again around the cylinder.
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Draw onto the “paper strip” the lines of the tooth points at the correct bevel angle. Actually, you only need to draw one of them.
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Use command “FlowAlongSrf” to wrap the line on the “paper strip” (Rhino calls it the “base surface”), back around the cylinder.
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Execute command “Sweep 2 Rails” – one curve is the axial centreline, the other curve is the tooth-point line you drew. The cross-section is the gear wheel profile.
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“Cap” to make solid. All done, voila!