Introduction to Computer Aided Design and Drafting Unit I Big Idea Students will learn how to draw inner and outer arc tangents. Essential Questions In what ways can you set up your arcs to be tangent. Declarative Knowledge: 1. Students understand how to use all relevant software’s for this class. 2. Students understand how to use the arc command. 3. Students properly place arc’s in the correct locations given the various diameter’s and radius’. Procedural Knowledge: 1. Find all commands in AutoCAD or Inventor 2. Write short paragraph on how to create outer and inner circles. 3. CAD Software. 4. Use Drafting textbook for further instruction and save all their work. 5. Use Software to receive instruction and information. Key Vocabulary Radius Diameter Arc Center Point Tangent How to draw an Arc tangent to 2 arcs Drawing inner-arc tangents 1) Make sure that all your measurements of the circles are in radiuses (unless you are in inventor. If you are make sure it is in diameters). 2) Draw your two circles that you plan to connect with the arc. 3) The next steps involve some math so you may or may not need a calculator. 4) As you can see in the picture below, the radius of the big circle on the left plus the radius of the arc (that you won’t have made yet) is equal to 10, and the radius of the circle on the right plus the radius of the arc is equal to 7. This is what you need to know to find the center point for the arc. To find the distance of them you simply add the radius of one circle by the radius of the arc. (Ex. 6 + 4 = 10) 5) Now draw a circle with a radius of 10 outside of the circle on the left. Then draw a circle with a radius of 7 outside the circle on the right. 6) The intersection of the 2 new circles you drew intersect at two places. The intersection at the top gives you the center point for your arc. Draw a circle with a radius of that arc. (see figure on next page) 7) Finally delete the two circles that you found the center point with and trim the top of the circle that’s the arc. IF YOU ARE USING INVENTOR, DOUBLE YOUR MEASUREMENTS BECAUSE INVENTOR MEASURES EVERYTHING IN DIAMETERS. Drawing an outer-arc tangent to two circles 1) Repeat steps 1 through 3 or use the drawing you just made. 2) For this step you are going to subtract the radius of the arc (that you plan to make) by the radius of the left circle (14 – 6 = 8). The difference of the two will give you the radius of the circle outside of the circle on the left. Do the same process for the circle on the right side and you will get something like this: 3) Your center point of the arc will be the intersection at the top. Draw a circle for your arc with the desired radius (14). 4) Finally, delete and trim to finish your design. AGAIN! MAKE SURE YOU DOUBLE YOUR MEASUREMENTS IF YOU ARE USING INVENTOR! For more information refer to your Mechanical Drawing book (12th edition) page 114.