Introduction: More Sketching and Editing Techniques
1) In the ribbon, under Sketch, choose Trim.
Alternatively, use hotkey T.
2) Click the two lines that you want to trim away to create a "step" in the bottom of the triangle.
Notice that the line turns red before you trim it, so you know what you're removing.
3) Above the ribbon, click the disk icon to save your part. Give it a name, and save it inside the Shopbot push stick project.
4) In the ribbon, under Sketch, choose Fillet.
5) Click the vertical leg and the hypotenuse of the triangle.
6) Enter a dimension of 3 and hit Enter.
7) In the ribbon, under Sketch, choose Circle>Center Diameter Circle.
Alternatively, use hotkey C.
8) Click the center point of the fillet you just created.
9) Before clicking again, expand the circle and type 4. The circle will adjust to a diameter of 4". Then click Enter.
How to Edit Dimensions
If you created a piece of sketch geometry with inaccurate dimensions, Fusion 360 makes it easy to edit dimensions.
1) Enter hotkey D for Dimension Mode.
2) Double click the circle diameter dimension.
3) Re-enter 4 and hit Enter.