The cone is not an accident
A twist drill cuts with two lips meeting at a point, and the angle between them is the reason the bottom of the hole is a cone rather than a floor. How long that cone is falls out of one right triangle: the radius is the opposite side, the half angle is at the tip, so the point length is the radius divided by the tangent of the half angle.
Half an inch at 118 degrees gives 0.250 over tan 59, which is 0.15022 in. Most shops carry that as 150 thou for a half inch drill and scale it, and the scaling is exact — a one inch drill at the same grind has a 300 thou point, a quarter inch has 75. The angle is what changes it: the same half inch at 135 degrees gives 0.10355, nearly five thou less for every tenth of an inch of diameter.
Where it costs you a hole
Blind tapped holes. The print says one inch of full diameter, you set the stop to one inch measured from the point touching, and the straight part of the hole is 0.850 deep instead. At 13 threads to the inch that is nearly two threads of engagement gone, which is the difference between a fastener that pulls up and one that strips at torque. Adding the point length to the travel puts it back, and the depth mic will then read 1.150 to the bottom of the cone, which is the number that confuses people who did the job right.
Through holes fail the other way. Set the travel to the material thickness and the drill has only just touched the far face when it stops — the full diameter is still 150 thou short of coming through and the hole is a cone at the exit. The travel has to include the point plus whatever clearance you want past breakout.
What a pilot hole actually changes
A pilot removes the middle of the cone, including the chisel edge that does no cutting and all of the thrust. What is left for the point to do is the annulus from the pilot diameter out to full diameter, so the travel before the full diameter arrives drops in proportion. A quarter inch pilot under a half inch drill halves the point travel from 150 thou to 75.
That is a depth effect, not a strength one. The pilot also changes how the drill behaves entirely — thrust falls, the drill follows the pilot rather than wandering, and at breakout there is less material left to grab. The page only counts the depth part, because that is the part it can know.
Pecking, and the number that governs it
Depth divided by diameter is the figure that decides whether a hole is routine or a nuisance. The default here is 1.150 of travel on a half inch drill, which is 2.3 diameters, and standard jobber flutes handle that without much thought. Past about five diameters the swarf has a long way to come out, the flutes pack, and the drill starts to bind on the chips rather than the metal. That is when pecking stops being optional.
The peck count here is the travel divided by the peck depth rounded up, and it prints the last peck separately because an uneven last peck of a few thou is worse than useless — the drill rubs. The even peck figure gives the same number of retracts with all of them the same size, which is usually the better plan.
The input this page most wants you to check
The point angle. Everything above scales with it and almost nobody measures it. A drill that has been resharpened freehand is somewhere between 110 and 140 degrees depending on who did it and how tired they were, and the two flanks are frequently not the same, which is a separate and worse problem: one lip cuts, the hole comes out oversize, and the point length is not a single number at all. A drill point gauge answers it in seconds. The 118 sitting in the field is a placeholder to replace, not a fact about your drill.
Questions people ask
How do I calculate drill point length?
Divide half the drill diameter by the tangent of half the included point angle. A 0.500 in drill ground to 118 degrees gives 0.250 divided by tan 59, which is 0.1502 in. The result scales directly with diameter at a fixed angle, so a one inch drill at the same grind has a 0.300 in point and a quarter inch has 0.075.
How deep do I drill for a blind hole of a given depth?
Add the point length to the depth of full diameter you want. For one inch of full diameter with a half inch drill at 118 degrees, the quill travels 1.150 in from the point touching the surface, and a depth mic will then read 1.150 to the bottom of the cone. Setting the stop at 1.000 leaves only 0.850 of usable straight hole, which on a blind tapped hole costs about two threads.
How much extra travel does a through hole need?
The material thickness plus the point length plus whatever you want past breakout. Stopping at the thickness leaves the tip just touching the far face with the full diameter still 150 thou short on a half inch 118 degree drill, so the exit is a cone rather than a hole. The distance between first breakout and a clean full diameter is exactly the point length, and it is also where the drill grabs.
Does a pilot hole change the drilling depth?
Yes. The pilot removes the middle of the cone, so only the annulus from the pilot diameter to full diameter is left for the point to cut through. A quarter inch pilot under a half inch drill halves the point travel from 150 thou to 75. The calculator subtracts it from the travel automatically once you enter the pilot diameter.
What point angle should I use?
That is a tooling question and this page does not answer it — the angle in the field is a placeholder for whatever your drill is actually ground to, which you measure with a point gauge rather than assume. What the page will tell you is the consequence: on a half inch drill, the difference between a 118 and a 135 grind is 47 thou of point length, which is nearly two threads on a blind tapped hole.