Make a vertical line p/4 (circular pitch) away from it and reflect the line over it. Draw up from the root line a line at the pressure angle from the vertical. Use circular pattern to make the rest of the teeth.įor a rack, draw three horizontal lines at with spacing 1/P. Use some reasonable fillets on the ends and roots of the teeth. You have the other side of this toothĭraw radials to connect to the root circle and a cap line or arc at the outer diameter. Draw another radial at 360/N/4 degrees away from that point where N is number of teethon the concave side of the involute. You can stop when the involute crosses the outer diameter.ĭraw a radial to the point where the involute touches the pitch circle. Now draw a spline connecting the ends of all these lines. 10 pi/90 * B, 20pi/90 * B, 30*pi/90 * B, … where B is the diameter of the Base circle. Now, set the length of each of the perpendiculars to the arc length away from the first point, i.e. Make the same thing a couple of times at intervals of 10 degrees or something. Make a radial and a perpendicular to that radial and tangent to the base circle. Write down the radius of the base circle. These two lines should intersect at 90 degrees. Make a line at the pressure angle from the pitch perpendicular you drew. Make another radial line at the pressure angle from the first. Make a perpendicular to that line touching the pitch circle. Now we need to find the base circle, the circle from which the involute is unrolled. Draw the root circle, pitch circle, and outer diameter circle. The root diameter is Pitch Diameter - 1/P = The root diameter is Pitch Diameter - 2/P =įor a rack, it’s much easier to work with p The outer diameter is Pitch Diameter + 2/P = If two gears have the same diametral pitch and pressure angle (and appropriate tooth profiles) they’ll mesh.įor a rack, the teeth are straight lines with the pressure angle with respect to the normal. Pressure angle is the angle between tooth profile and diameter at the pitch point. $ p P = \pi$Īt the height of the pitch circle there is just as much tooth as tooth gap. The circular pitch p is the distance between the same point on each tooth. It must have units of inverse inches typically. The diametral pitch is the number of teeth divided by the pitch diameter. This tells you how far apart to mount the two gears The pitch diameter is how far that point will be from the center of the gear. The pitch point is the point of contact between two gears that lies between their centers. Some good resource books are Shigley’s Mechanical Engineering Design, Machinery Handbook and these sites They are involute curves, curves traced out by
However, using circular arcs for the gear teeth is not correct. Could use openscad but not super comfortable with it and I kind of don’t like how the gear library draws the gears. You can make stacked gears using the union function to make the pieces of a differential gear train
#Openscad gear library plus
It’s in the plus sign at the right hand side of the menu bar.
#Openscad gear library generator
UPDATE: NVM. Use the gear generator feature.
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