Point Geometry Comparison: Conventional vs Split vs Notched

The Three Major Point Geometries

Drill point geometry determines how the drill enters the material, how much thrust force is required, and how the hole starts. Getting the geometry right for your application can mean the difference between a hole that starts on location and runs true versus one that walks, tears, or requires a spotting operation you could have avoided.

Conventional 118-degree point is the baseline — what most people picture when they think of a drill. The 118-degree included angle is a historical compromise that works adequately in a wide range of materials without specialized grinding equipment. The chisel edge at the center doesn't cut; it extrudes material by pushing it outward toward the lips. This creates a characteristic "tent" of extruded material at the hole entrance in ductile metals, and it means roughly 50 to 60 percent of the thrust force in drilling is consumed just by the chisel edge pushing material rather than cutting it.

Split point geometry addresses the chisel edge problem directly. By grinding a secondary relief behind the chisel edge, the split point creates two additional small cutting edges at the center of the drill. These small edges actually cut rather than extrude, dramatically reducing thrust force — typically 30 to 50 percent less thrust than a conventional point of the same diameter. The drill also self-centers better: there's less lateral force pushing the drill away from center on entry, which reduces walk and often eliminates the need for a spotting operation.

Notched or web-thinned point is a variation on the split point concept. Where a split point is ground with a secondary face, a notched point grinds a small notch behind each lip to thin the web at the center. The effect on thrust and self-centering is similar to a split point, but notched geometry is simpler to produce on some grinders. Many production drills sold as "split point" are technically notched — the functional difference is minor in most applications.

Application Matrix: Which Geometry for Which Job

Choosing between these geometries is an application decision, not a quality decision — the "best" geometry depends entirely on what you're drilling and how:

• Mild steel, CNC production, tight location tolerance: Split point. Lower thrust reduces workpiece movement on fixture, better self-centering reduces or eliminates spotting cycle. Worth the slight cost premium on high-volume jobs.
• Stainless steel, titanium, or other work-hardening alloys: Split point mandatory. Reduced thrust means less rubbing, less heat, less work hardening ahead of the cut. Conventional point in stainless often fails prematurely from the rubbing action of the chisel edge.
• Cast iron, hard plastics, composites: Conventional point is acceptable; split point doesn't hurt. These brittle materials don't suffer as much from chisel edge extrusion since they fracture rather than deform. Some specialty geometries exist for composites that minimize delamination.
• Aluminum, copper, soft brass: Either geometry works. High-helix drills with conventional points are common and effective. Some operators prefer split point for better self-centering, but the soft material allows conventional points to perform well.
• Hand drilling, portable drill press, flexible setup: Split point is preferred for its self-centering advantage, especially when you can't use a spotting drill first. The reduced thrust also makes hand drilling less fatiguing.
• Deep holes in tough material: Split point. Every reduction in thrust force reduces the bending moment on the drill in a deep hole, reducing the risk of wandering and breakage.

Reconditioning Considerations by Geometry

All three point geometries are grindable and reconditionable, but they're not all equally straightforward to regrind correctly. Conventional 118-degree points are the simplest — almost any drill grinder can produce them accurately. Split point geometry requires a grinder capable of the secondary relief grind — CNC dedicated drill grinders handle this routinely, but bench grinders and simple fixtures can't produce accurate split points.

This matters when you're choosing a reconditioning service. A service that regrind splits points as conventional points is reducing your drill's performance, even if the geometry looks sharp. Ask specifically whether the service preserves split point geometry on drills sent in with split points. At MachinistPost, split point geometry is maintained through the reconditioning process — the WinsloMatic handles both conventional and split point in the same grinding cycle.

Drills with worn or damaged split points can also be reground to conventional points — a valid choice when the split-point geometry is too damaged to restore. In most production applications the conventional regrind performs acceptably, with the understanding that you'll likely need to restore spot-drilling steps that the split point was eliminating.