Suggested Technique for Creating an Involute Gear
Create default datum planes by selecting Insert, Datum Plane.
Create a disk (Create, Protrusion, Extrude, Solid,
Done, Both Sides, Done) sketched on DTM3 with the
center at the intersection of DTM2 and DTM1. The depth of the disk will be
Next, create an angled datum plane by selecting Insert, Datum, Plane,Through,
select A_1 (created from the protruded disk). Then select Angle, and
select DTM2. Enter an angular dimension for the DTM 4 location.
Sketch a datum curve on the front surface of the disk. The curve should be
an arc with the center on A_1. The radius of the arc, arc length, and the
angle between the endpoint of the arc and DTM4 should be dimensioned. The
disk with this first datum curve is shown in Figure 1 below.
Project the datum curve created in Step 4 to the back surface of the disk by
selecting Insert, Datum, Curve, Projected, and Done.
Select Select and Done from the PRJCRVTYP menu. Select the
datum curve created in Step 4 to be projected, select the back surface of
the disk to project the datum curve onto, select Along Dir and Done
from the PROJ TYPE menu and DTM3 for direction reference. If necessary,
flip the direction arrow to point in the direction of the back surface of
These two curves will now be used as the spine and x-vector for a surface
created using a variable section sweep. To create this feature, select Create,
Surface, New, Advanced, Var Sec Swp, Done,
NrmToOriginTraj, Done. Select the curve created on the front
of the disk as the spine and the curve create on the back of the disk as the
x-trajectory. In sketcher mode, create the sweep's section as a horizontal
line just above the datum curves. Dimension this line vertically to A_1 and
align the end points to the flat faces of the disk. Write the following
sketcher relations to create the desired curve to this surface:
rbase = 2.0
todeg = 180/pi
a = 1.0
sd4 = rbase*(1+a^2)^.5
PLEASE NOTE: The relations used in this example are for
illustrative purposes only and should be modified to meet the requirements
and design intent of the object being modeled.
The dimension sd4 refers to the distance between the axis and the
sketched line.The value of 14.0 should be substituted with the number of
degrees used for the length of the first datum curve and the 2.0 is the
radius of the root circle for the gear. The variable "a" is used
to solve for the dimension value and is set to 1.0 to initialize it so that
it can be used to solve the equation. After regenerating, sd4 should snap to
2.0, the radius of the root circle. Regenerate the model and select Done.
The involute surface created is shown below in Figure 2.
Next, miror the involute surface about DTM4 by selecting Create, Surface,
Transform, Mirror, Copy, Done. Create a
cylindrical surface along A_1 with a radius slightly greater that the value
for the radius of the root circle of the gear to connect the surface created
in Step 6 with the mirror just created. Merge these 3 surfaces together. The
resultant surface is shown below in Figure 3. The datum planes have been
removed from this figure for clarity.
Finally, transform rotate the merged surface about A_1 utilizing the same
technique in Step 7 and pattern 360 degrees. Create a reference pattern of
cuts, via Use Quilt, to create the teeth. For more information
about surface transform, refer to Suggested Technique for Creating a
Rotational Pattern Using a Surface Transform. Two adjacent cuts will
create a single tooth. The completed involute gear is shown below in