A countersunk hole is a cone-shaped recess in an object, designed to accommodate a flat-head screw such that the head of the screw is flush with the surface of the part. Countersunk holes are represented in engineering drawings in a standard way to make the production and manufacturing process easier and more efficient. These drawing standards are set by groups such as American Society of Mechanical Engineers or American National Standards Institute to serve as guidelines for engineers or draftspersons and are not required by law.
Inches or Standard Measurement
Video of the Day
Step 1
Draw the leader, or dimension line, with the arrow just touching the edge of the outer circle of the countersunk hole. Draw the line radially, so that it points toward the center of the hole, and if extended it would pass through the center point.
Video of the Day
Step 2
Write the dimensions of the countersink, giving first the diameter of the drill hole, then the angle of the countersink, followed by the diameter symbol and the diameter of the larger hole. This dimension can be given either with a diameter symbol first, or with the word DRILL after the first diameter.
Step 3
Add the number of holes, if there are more than one. It is only necessary to dimension one of the holes. Use the format 3 HOLES, where 3 is the number of holes.
Metric
Step 1
Draw the leader, or dimension line, with the arrow just touching the edge of the outer circle of the countersunk hole. Draw the line radially, so that it points toward the center of the hole, and if extended it would pass through the center point.
Step 2
Write the number of holes. Use the format 3X, where 3 is the number of holes. Follow with the diameter symbol and the diameter of the hole. It is only necessary to dimension one hole.
Step 3
Draw the ASME countersink symbol. Follow with the diameter symbol and diameter of the larger countersink hole. Add the angle of the countersink.