Look at a drill from the end. The web is the solid cylinder of material at the center of the drill — the core that connects the two flutes. The cutting lips extend outward from the web to the outer diameter. The chisel edge sits at the intersection of the two fluted faces at the center, running across the web.
The web is structural. It keeps the drill from twisting apart under torque and provides the column strength to resist buckling under axial load. A drill without sufficient web thickness would flex, deflect, and snap. The web has to be there.
But the web doesn't cut. The chisel edge that spans it scrubs rather than shears because it has near-zero surface velocity and no effective rake angle. The wider the chisel edge — and chisel edge width is directly related to web thickness — the more thrust force is required to push the drill through the material and the more work-hardening pressure is applied ahead of the cut.
Web thickness is specified as a percentage of drill diameter or as an absolute dimension. On a standard drill, it typically runs from around 12–15% of diameter at the tip, increasing toward the shank due to the taper ground into the flutes.
Here's the geometry that creates the problem: the web is not a uniform cylinder. It's a tapered body — thicker near the shank, thinner near the tip. This taper is designed into the drill so that as the tip wears and gets resharpened, there's sufficient material at the new tip to grind a fresh cutting edge.
Every resharpen removes material from the tip, moving the effective cutting point slightly back toward the shank. And as you move toward the shank, the web is thicker.
The result: a drill that started with a web 15% of its diameter at the tip may, after three or four resharpens, have a web that's 20–25% of its diameter at the (now shorter, more rearward) tip. The absolute drill diameter hasn't changed. The absolute web thickness has increased. The ratio has shifted unfavorably.
This is not a subtle effect. A drill with a web that's gone from 15% to 25% of diameter requires measurably more thrust to drive through the material. In hard materials or on machines with limited spindle thrust, the drill may stop cutting and start scrubbing, generating heat rather than chips. In stainless or titanium, this directly causes work hardening ahead of the tip — the death spiral that leads to burnt edges and snapped drills.
The other thing that happens: as the web thickens, the chisel edge gets longer. A longer chisel edge means more wandering at startup, more thrust required to engage, and more compressed material ahead of the point before the lips begin their cut.
Web thinning is a secondary grinding operation performed as part of resharpening. It removes material from the heel of each flute near the tip to thin the web back to an appropriate thickness for the current length of the drill. On a WinsloMatic or equivalent drill grinding machine, this is a specific fixture operation performed after the primary point grind.
The result is a shorter chisel edge, reduced thrust requirements, and cutting performance closer to what the drill had when new — even after multiple resharpening cycles.
When is web thinning necessary?
Web thinning is not always required on a light resharpen of a drill that's only been used a few times. If the point geometry is still good and the drill is close to full length, a standard point regrind is often sufficient.
If your shop sends drills out for reconditioning on a regular cycle, web thinning should be part of the specification for any drill that's been resharpened before. Mention it explicitly if you're communicating with your reconditioning service — "regrind with web thinning" versus "standard regrind" produces different results.
A drill returned with proper web thinning will behave more like a new drill in terms of thrust requirements and startup behavior. A drill returned with only a point regrind will have a sharp edge but a chisel edge that keeps getting relatively wider with each cycle.
The practical takeaway: don't just track when a drill gets resharpened — track how many times. Drills past their second or third cycle should always get web thinning. That's the maintenance step that actually restores performance, not just the edge.
Mail in your dull HSS drills. We'll sharpen them on our WinsloMatic — back to spec, ready to cut.
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