Dimensioning Arcs, Holes & Circles

1. Dimensioning Arcs, Holes & Circles By: Mitch Hobbs, Blake Bentzen, Tor Eimon, Ben Metzman, Joaquin Gurza,Scarlett Johansen, Brian Fay, Elan Safford

2. Rules For Dimensioning Arcs Rule G: • Rounded inside corners of an object are known as fillets. Rule H: • Rounded outside corners of an object are known as rounds. • Rounds are dimensioned with notes.

3. Rules For Dimensioning Arcs Rule I: • When a complete radius dimension can’t be shown to scale because it is outside the drawing or competes with another view, the dimension line may be foreshortened with a short break or zig-zag in it. R 3

4. Rules for Dimensioning Arcs (Fig-1) • Extension and dimension lines are used to find the center of an Arc (Fig-1) • If necessary, the arrowhead may be also placed outside the object (Fig-2) (Fig-2)

5. Rules for Dimensioning Arcs • When a part has a number of radii the same size, a note may be used for all arcs of the same size instead of dimensioning of each radius separately (Fig-3)

6. Dimensioning Arcs cont. • A dimension line should be drawn from the center to the circumference of the arc. The arrow should touch the circumference. A number indicating the size of the arc is placed within this dimension line. • The center point of the arc should be indicated with two short perpendicular lines (⅛”). • If space is limited, a leader line may be used in conjunction with a dimension line. The number is then moved outside the arc and centered at the end of the shoulder of the leader. R 1/8 R 7/8

7. Rules for Dimensioning Circles & Holes • Use a Leader Line to dimension a circle or hole • The Diameter can be on the circle, only if its needed to clarify the dimension • Always locate a hole from its center Ø3/8” Ø3/8” ¾”

8. Dimensioning Circles & Holes • If several circles are to be dimensioned, they may be located by dimensioning center to center. • Equally spaced holes may be dimensioned only once • Cylinders are dimensioned by a side view Ø3/8” 1” Ø3/8” 1” Ø3/8”

9. Rules for Dimensioning Circles & Holes • Partial views can be used to describe cylindrical objects if they are symmetrical. • To dimension holes, give the diameter as well as the depth and the number of holes needed (in that order). • A hole that does not pass all the way through the object is called a “blind hole”. You must give the depth of a blind hole. • If there’s only one hole to be dimensioned, numbered holes are not needed.

10. Dimensioning Circles & Holes • Ø is used to denote that the dimension is a diameter. Ø 1/2 3/8 7/16 Ø 3/8 Ø1/2

11. The End