Drill Point Length Calculator with Z Depth and Drilling Time
A drill does not cut a flat-bottomed hole, so the programmed Z depth must include the conical point. This calculator turns diameter and point angle into point length, the Z travel to program, spindle speed, feed and drilling time.
Your numbers
Selecting an angle sets the factor 1 / (2 x tan(half angle)).
Depth of the hole at full diameter, measured from the surface.
Use the drill maker's value for your material and coating.
Your results
Speeds and feeds are inputs you choose from your tooling data. Pecking, dwell and rapid moves are not included in the time.
Drilling time versus drill diameter
Sweeps Drill diameter from 3 to 30, holding your other inputs fixed.
Compare your standard times with real cycles
If you want routing times checked against machine data, tell us your ERP and we will suggest what to compare.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the drill diameter, choose the point angle printed on the drill, and set the depth of hole you need at full diameter. Add your cutting speed and feed per revolution from the tool catalogue. The calculator returns the point length and the Z travel to program. For a through hole the point must clear the exit, so add the point length and a small breakout allowance to the part thickness. For a blind hole the programmed Z depth is the full-diameter depth plus point length.
- Point angle is printed on most drill shanks or catalogue
- Depth is full-diameter depth, not tip depth
- Add breakout allowance for through holes
The formula
The point length equals half the diameter divided by the tangent of half the point angle. For a 118 degree point the factor is about 0.30 of the diameter, so a 10 mm drill has a point near 3.0 mm. For 135 degree points the factor is about 0.21, giving a 10 mm drill a 2.1 mm point. Spindle speed follows the usual rpm equals 1000 times cutting speed divided by pi times diameter, and feed rate is rpm times feed per revolution.
Reading the results
The Z travel is what you place in a G81 or G83 cycle as the final depth, measured to the tip. A flatter 135 degree point reduces the extra travel and self-centres well on most steels, while a steeper 118 degree point is a general-purpose choice. The depth to diameter ratio flags when a plain drilling cycle may not evacuate chips. The time output is feed time only, so peck cycles, dwell and rapids will lengthen the actual cycle.
Common mistakes
Programmers sometimes forget the point and leave a blind hole short of the drawing depth, or they use the same factor for all drills when a split-point 135 degree drill is in the spindle. Another is mixing inch speeds with mm diameters. Check that the unit of every value matches.
- Use the actual point angle of the drill in the holder
- Remember tolerance on hole depth
- Keep units consistent
Frequently Asked Questions
How long is the point of a 118 degree drill?
About 0.30 times the drill diameter. A 10 mm drill with a 118 degree point has a point length close to 3.0 mm, calculated as half the diameter divided by the tangent of 59 degrees.
Do I add the point length to the hole depth?
Yes, when the drawing depth refers to the full-diameter portion of the hole. Add the point length so the tool reaches full depth. If the drawing dimension refers to the tip, use it directly.
Why choose a 135 degree point?
A 135 degree point usually has a split point that centres without a pilot and shortens the conical portion. It is common on carbide and cobalt drills for harder materials, while 118 degrees remains a common general-purpose choice.
Does the time include pecking?
No. The time is the feed move from the approach plane to the programmed depth at the stated feed. Pecking cycles, dwell, retracts and rapids add to it, so add allowances for those if you cost deep holes.
If cycle times and tooling data are maintained in routings inside your ERP, we can help compare standard times with what this kind of calculation predicts.
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