Advanced Calculator
Drill Point Length Chart
Formula Used
Drill Point Length = D / 2 × tan(A / 2)
Correct written form:
L = D / (2 × tan(A / 2))
Where:
L is drill point length. D is drill diameter. A is included drill point angle.
Total Drill Travel = Straight Hole Depth + Drill Point Length
How to Use This Calculator
Enter the drill diameter first. Use the same unit you use for your job.
Enter the included point angle. Common twist drills often use 118 degrees.
Enter the straight hole depth needed after the drill reaches full diameter.
Press the calculate button. The result appears above the form.
Use the chart to compare point length changes across drill angles.
Download the CSV or PDF file for shop records, quotes, or setup sheets.
Example Data Table
| Diameter | Point Angle | Point Length | Use Case |
|---|---|---|---|
| 10 mm | 118° | 3.00 mm | General drilling |
| 12 mm | 135° | 2.49 mm | Hard metal drilling |
| 8 mm | 90° | 4.00 mm | Sharper point setup |
| 0.5 in | 118° | 0.150 in | Imperial workshop setup |
Drill Point Length in Physics and Workshop Geometry
Why Point Length Matters
Drill point length is the axial distance from the drill tip to the point where the drill reaches full diameter. It is a small value, but it can change the final depth of a hole. This matters in machining, metal work, wood work, plastics, and layout planning.
Geometry Behind the Drill Tip
The drill tip forms a cone. The included point angle creates two equal half angles. The drill radius forms the opposite side of a right triangle. The point length forms the adjacent side. Tangent connects these values. This makes the calculation simple and reliable.
Depth Control
A drilled blind hole is not flat at the bottom. The cone-shaped tip adds extra travel beyond the straight cylindrical depth. If a drawing needs a full diameter depth, the point length must be added. This prevents shallow holes and poor part fit.
Angle Effect
A smaller point angle creates a longer point. A larger point angle creates a shorter point. A 90 degree point is deeper than a 135 degree point for the same drill diameter. This is why drill geometry affects setup values.
Practical Planning
Use this calculator before drilling precision parts. It helps estimate total travel, compare drill angles, and prepare consistent depth stops. It is also useful for CNC setup sheets, manual drilling checks, and engineering notes.
Better Decisions
Good geometry reduces mistakes. It improves hole accuracy and supports better tool planning. Always confirm material behavior, tool condition, machine rigidity, and drawing requirements before final machining.
FAQs
1. What is drill point length?
It is the distance from the drill tip to the place where the drill reaches full diameter.
2. Why is drill point length important?
It helps calculate total drill travel, especially when a full diameter blind hole depth is required.
3. What angle is common for twist drills?
A 118 degree point angle is common for general drilling tasks and many standard twist drills.
4. Does a larger point angle reduce point length?
Yes. A larger point angle creates a flatter drill tip and reduces the axial point length.
5. Can I use inches instead of millimeters?
Yes. Use any unit, but keep diameter and depth in the same unit for correct results.
6. Is this useful for CNC drilling?
Yes. It helps estimate programmed depth when full diameter depth is required in blind holes.
7. Does this replace machine setup checks?
No. It supports planning, but tool wear, runout, material, and machine condition should be checked.
8. What formula does this calculator use?
It uses L = D / (2 × tan(A / 2)), based on drill tip triangle geometry.