GEAR GENERATION

In BobCAD-CAM Version 21 the Involute Gear is drawn with small arc segments that can be machined in the NC CAM (G01, G02, G03). Here is the new gear box below.

These attributes include:

• Number of teeth. This is basically the number of teeth that you need the gear to have.
• Pressure Angle. This is the angle between the tooth profile and the radial line at its pitch point. Also described as the angle between the line of action and the line tangent to the pitch circle. More information on this can be attained through your Machinist Handbook.
• Pitch Diameter. This is the diameter of the pitch circle. The operating pitch diameter is the pitch diameter at which the gear operates.
• Outside Diameter. This is the diameter of the circle that contains the tops of the teeth of external gears.
• Root Diameter. This is the diameter of the circle that contains the roots or bottoms of the tooth spaces.
• Root Fillet Radius. This is the radius of the concave portion of the tooth profile where it joins the bottom of the tooth space.

These definitions can be seen in the GEARING section of the Machinist/Machinery’s Handbook. You simply enter in the values needed to create your gear and click the OK button to draw the complete gear. You can use the X, Y and/or Z values as needed for placing the gear on the CAD screen.

Here it is again in a diagram:

QUICK GEAR LESSON:

STEP 1

Open the software and select GEAR from the OTHER main menu.

STEP 2

Enter the following:

· 16 for the number of teeth.

· 20 for the Pressure Angle.

· 3.75 for the Pitch Diameter.

· 4.25 for the Outer Diameter.

· 3.15 for the Root Diameter.

· .06 for the Root Fillet Radius.

Click OK to see the result.

You have completed this lesson.