The Part of the Drill That Doesn't Cut
When you look at the tip of a twist drill, most of what you see is the cutting edges — the two flutes that spiral up the body, ground to a point angle that slices into the workpiece. But right at the very center of the drill tip is a feature that doesn't cut at all: the web.
The web is the solid cylindrical core running down the length of the drill. It's what gives the drill its structural rigidity. Without it, a drill under axial load would buckle. The web is load-bearing, not cutting.
The problem is that the web doesn't cut — it scrapes and pushes. The short horizontal edge formed where the two flute faces meet at the web is called the chisel edge, and at cutting speed, the chisel edge is essentially extruding metal sideways rather than shearing it cleanly. It requires significantly more thrust force than the cutting lips do, generates more heat at center, and is the reason drilling requires substantially more downforce than turning or milling of similar material.
What Happens to the Web as a Drill Is Resharpened
Here's the part most operators don't think about: every resharpen removes material from the tip of the drill. The drill gets shorter. And because the web tapers — it's thicker toward the shank than at the tip — shortening the drill means the web diameter at the new tip is larger than it was at the original tip.
A brand-new 1/2" drill might have a web thickness of around .060" at the tip. After several resharps, that same drill might show a web of .090" or more. The chisel edge has grown. The non-cutting zone is now a bigger fraction of the drill diameter. Thrust force requirements go up. Heat at the centerline increases. The drill starts to "walk" on entry rather than self-centering.
This is not a resharpening defect — it's geometry. It happens to every drill that gets resharpened without web thinning. The solution is to relieve material near the chisel edge to bring the effective web thickness back down to spec.
What Web Thinning Actually Does
Web thinning is a secondary grinding operation performed at the drill tip after the primary point angle is established. Material is removed from the heel of each cutting lip near the center, effectively shortening the chisel edge and creating a more aggressive cutting geometry at the drill's center.
There are several web thinning styles — notch, split point, crankshaft — each with different geometry and application. The goal of all of them is the same: reduce the chisel edge length so the drill requires less thrust force and starts cutting closer to center rather than pushing.
A properly web-thinned drill drills faster, runs cooler at the tip, requires less feed pressure, and self-centers more reliably on entry. On CNC machines with fixed feedrates, an un-thinned drill can overload the spindle, break the drill, or produce an oversized hole from the lateral force of the oversized chisel edge.
Signs Your Drill Needs Web Thinning
You don't always need a micrometer to know something's off. Here are the practical indicators:
- High thrust force on entry. If you're pushing noticeably harder than you used to for the same drill and material, the web has grown.
- Drill "walking" on entry. A drill that wanders across the surface before engaging is often chisel-edge-dominant. A spot drill or center punch helps, but web thinning fixes the root cause.
- Needing a center mark. If operators have started center-punching before drilling on work that didn't require it before, web growth is the likely culprit.
- Heat discoloration near drill tip. Excess heat at center — the chisel edge zone — shows up as dark discoloration or blueing on the drill tip after use.
- Chatter or vibration on entry. The lateral force from a thick chisel edge can cause instability, especially in less rigid setups.
How MachinistPost Handles Web Thinning
Web thinning isn't a premium add-on at MachinistPost. It's standard on every resharpen.
The Giddings & Lewis WinsloMatic grinder used to regrind customer drills is a precision point-grinding machine designed for exactly this kind of work. After the primary point angle is established, web thinning is applied as part of the standard regrind process. Customers don't need to request it or pay extra — it's part of what a properly resharpened drill means.
This matters because a drill resharpened without web thinning will perform worse than expected, especially after multiple sharpening cycles. If your shop has been getting drills back from resharpening and finding they still require more thrust than new drills, inadequate web thinning is a likely explanation.
Web Thickness as a Quality Check
A good way to evaluate a resharpen — whether done in-house or by a service — is to check web thickness before and after. For most standard twist drills, the original web thickness runs approximately 12–15% of drill diameter at the tip. After resharpening, the web at the new tip should be thinned back to approximately that ratio, or at minimum reduced from what it was before.
If you're measuring a freshly resharpened drill and the web is visibly thick relative to the diameter, or if the chisel edge length is more than about 15% of the diameter, the drill hasn't been fully reconditioned.
The Bottom Line
Web thinning is not optional for drills that have been resharpened more than once. It's a required step to restore the drill's original cutting efficiency at center. Skipping it produces a drill that technically has the right point angle but still drills poorly — more thrust, more heat, more tendency to walk.
MachinistPost includes web thinning on every resharpen, no exceptions. Mail in your worn HSS drills and get back tools that drill like new — not just tools with a fresh point angle. Pricing starts at $3.00 per drill, any carrier, $20 order minimum.