Shop Solver

Countersinks/Counterbores

Command path:  Tools->C'Sinks/C'Bores
This tool has 3 features:

1) It calculates the depth of cut for a countersink with a specified included angle to obtain a desired diameter.
2) As an aid for measuring, it calculates the height of any size ball that is in contact with the countersink, and the adjustment to the tool depth needed to bring the countersink diameter to size.
3) A reference tool that provides clearance hole and counterbore diameters for inch and metric cap screws.


Tool Image




Countersink Depth Calculator

The Countersink Depth Calculator determines the depth of cut required to obtain a specified countersink diameter.  It consists of 3 entry fields and the calculated depth of cut.  The 3 entry fields are:

• Included Angle:  A drop-down list of common included angles.  You may select an angle from the list or enter a custom angle in the entry field.
• Flat Diameter:  The diameter of the flat ground onto the bottom of the countersink.  A flat diameter of zero assumes the countersink has a theoretical sharp point.  See Figure 11 below.
• Countersink Diameter:  The desired diameter of the countersink.

Figure 11 depicts an 82 degree countersink with a flat diameter of .250".  Using it as an example, to obtain a .500" diameter countersink:

1) Select 82 from the Included Angle  drop-down list or enter 82 into the entry field.
2) Enter .25 into the Flat Diameter  entry field.
3) Enter .5 into the Countersink Diameter  entry field.
4) Press Enter  or tab to or click on any other field.  The depth of cut (0.1438) is shown in the Depth  label below the Countersink Diameter  entry field.

The calculator can also be used to determine the length of a drill point.  For example, to determine the drill point length of a .375" diameter drill with a standard 118 degree grind:

1) Select 118 from the Included Angle  drop-down list.
2) Enter 0 into the Flat Diameter  entry field.
3) Enter .375 into the Countersink Diameter  entry field.
4) Press Enter  or tab to or click on any other field.  The length of the drill point (0.1127) is shown in the Depth  label.


Countersink Ball Measurement

The Countersink Ball Measurement section calculates the height of any size ball that is in contact with the countersink.  It also calculates the depth adjustment required to obtain the desired diameter.

Figure 11a below shows 3 examples of different diameter balls used to measure an 82 degree countersink that is .75" in diameter.  The balls are shown in red along with the distances from the surface plane to the tops of the balls.  The image on the left depicts a ball that only contacts the countersink along its rim where the flat surface plane intersects the cone of the countersink.  The image in the middle depicts a ball that contacts the surface of the countersink's cone and extends above the surface plane.  The image on the right depicts a ball that contacts the surface of the countersink's cone and lies below the surface plane.


To determine the height of a specified ball diameter above or below the surface plane:

1) Use the Countersink Depth Calculator as described above to determine the depth of the countersink.
2) Enter the ball diameter in the Ball Diameter  field.
3) Press Enter  or tab to or click on any other field.  The height of the top of the ball is shown in the Target Height  label.

To determine the distance required to increase or decrease the depth of the countersink in order to obtain the desired diameter (assuming the material has already been countersunk):

1) Calculate the target height of the ball as described above.
2) Measure the height of the top of the ball resting in or on the countersink and enter the distance in the Current Height  field.
3) Press Enter  or tab to or click on any other field.  The distance required to increase or decrease the depth of cut is shown in the Depth Adjustment  label.  Positive values mean that the countersink's depth of cut must be increased; negative values mean that the countersink's depth of cut must be decreased.


Cap Screw Clearances

As shown in the Tool Image above, select either "Inch" or "Metric" and the screw size from the drop-down list.  The counterbore and clearance hole dimensions are shown in the fields below the drop-down list.