Tool Regrinding
& Reconditioning

Why Regrind a Deep Hole Tool?

Deep hole tooling is among the most expensive consumables on the shop floor — and the one most often scrapped too early. A gundrill typically dulls after roughly 1,000 inches of drilling; resharpened correctly, the same drill performs as well as a new one 8–10 times. The only physical differences from a new tool are a slight back taper and reduced solid carbide length at the tip. Regrinding turns that cost center into a recurring, controllable spend.

How Many Regrinds Per Tool?

How many resharpenings a tool supports depends on the tool family and the carbide available at the cutting end. The practical limits below are what manufacturers and reconditioning services quote in production.

What changes with each regrind

• Each cycle removes a small amount of stock, so the flute shortens and the tip carbide length shrinks.
• A slight back taper develops as material is ground from the outer corner — normal, but it does reduce the usable diameter slightly.
• Track regrind count with laser marking on the shank: each mark is one cycle, making tools near their limit easy to spot.
• Reground too far, the remaining carbide gets thin and the tool becomes fracture-prone. At that point re-tip instead of regrind again.

Reading the Wear Signs

Regrind too early and you waste edge life; too late and you risk scrap or tool breakage. Wear accelerates rapidly once an edge dulls, so the window between "needs regrinding" and "dangerous" is shorter than most operators expect. Watch these five indicators.

Three tool-life management strategies

Regrind Geometry That Must Come Back

Regrinding restores three things: edge sharpness, clearance angles, and the apex/point geometry that balances inner and outer cutting forces. Research on gundrilling of Inconel 718 shows that inconsistent apex offset between successive drills produces unbalanced forces and measurable hole straightness deviation — consistent apex offset gives the smallest deviation. Never improvise geometry; regrind to the original tool specification.

The Regrind, Step by Step

On a CNC tool grinder, a full gundrill resharpening takes under 10 minutes once the machine is set up. The eight steps below restore edge geometry, clearance, and the coolant outlet.

Gundrill resharpening sequence

In-House Regrinding vs. External Service

Manufacturers choose among three paths: the original tool maker (OEM), a local sharpening service, or an in-house grinder. Each has a place — the decision turns on volume, tolerance requirements, and tool complexity.

Representative regrinding equipment

Commercial regrind / re-tip services

Coating Strategies After Regrind

Regrinding restores edge geometry but removes the protective coating from the ground surfaces. That leaves two recoating strategies, and the choice materially changes turnaround and performance.

• A drill can typically be recoated 5–10 times before stripping becomes necessary.
• Changing coating type at recoating — e.g. upgrading from TiN to TiAlN or AlCrN — can improve performance over the original, especially if the original coating was selected for a different material.
• On coated drills, regrinding removes coating from the cutting face but leaves it on the wear pads; tool life is somewhat reduced compared to a freshly coated edge.

Verifying a Reground Tool

Never judge a reground tool by appearance alone. A tool that looks perfect can hide grinding burns that weakened the carbide. Verify geometry and edge condition on every regrind, whether in-house or returned from a service.

• Measure geometry — point angle, relief angles, and tip diameter on a tool presetter or optical comparator.
• Inspect the edge at 10–20× — look for micro-chipping, grinding burns (blue or brown discoloration), or uneven edges.
• Confirm the apex dimension — point-to-center distance should be D/4; lip height difference within 0.02 mm.
• Check runout — axial runout within 0.02 mm on the returned tool; the grinder itself should target <0.005 mm.
• Verify the coolant outlet — the oil dub-off geometry must be fully restored or chip evacuation will fail in the bore.

Selecting a regrinding service

• Prefer the original manufacturer — they hold the geometry specifications, grinding fixtures, and coating recipes.
• Request a sample regrind — have 3–5 tools reground and prove them on production parts before committing volume.
• Verify geometry after return — measure point angle, relief angles, and tip diameter on a presetter.
• Check edge quality at 10–20× — micro-chipping, grinding burns, or uneven edges mean the regrind failed.

Regrinding Economics

Over the full life of a tool — new plus eight regrinds for a gundrill — total cost with regrinding is roughly 30–40% of the cost of buying nine new tools.

Regrindable vs. indexable insert drilling

Re-Tipping — The Last Life Cycle

When the carbide head of a gundrill or BTA drill has been reground to the point that insufficient carbide remains — typically after 8–10 regrinds — re-tipping is the next option. Re-tipping replaces the carbide cutting head on the existing steel shank or drill tube and saves up to 80% of the cost of a new tool. The shank is inspected for straightness and wear first; if the shank is damaged or the tube worn, a full new tool is required.

Re-tipping is offered by most major tool manufacturers and by specialist services (Mollart from Ø2 mm, botek, Sterling, RAMADA Aços/TBT, Star Cutter). Some services recondition the complete assembly — from the driver connection to the carbide tip — and engrave the final length so the tool is ready to mount on return.

Regrinding Mistakes That Cost Holes

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