Drill Point Angle from Tip Length
The included point angle from the diameter and a measured or target point length (tip allowance).
Example
You enter
- Drill diameter (in) 0.5
- Point length / tip allowance (in) 0.15
You get
- Included point angle 118.072
- Half (lip) angle 59.036
Checked against published worked examples from: Sundi Cutting Tools.
Details, formula, and sources
Scopeangle = 2 x atan( (diameter / 2) / point length ). A 0.5 in drill ground to a 0.15 in tip is a 118-degree point; a shorter tip is a blunter angle. The number you back out when you sharpen to a length or measure a tip on a comparator. Geometry only; the actual grind and web thinning govern.
Formula or tableincluded point angle = 2 x atan( (diameter / 2) / point length ); half (lip) angle = point angle / 2; the inverse of point length = (diameter / 2) / tan(point angle / 2).
Source and editionDrill-point geometry; the 118 / 135-degree drill-point relation as in Machinery's Handbook (Industrial Press), by name; first-principles trigonometry, solved for the angle.
Free accessPure geometry, public; web thinning, drift, and the actual grind govern the drilled hole.
What governsEstimate. AHJ and licensed professional govern.
API field namesdiameter_in, point_length_in, point_angle_deg, half_angle_deg
- Ideal conical point treats the point as an ideal cone; ignores web thinning and split-point geometrydrill-point geometry