How to Set Up a Drill Reconditioning Log

Why Most Shops Have No Idea What Their Drills Cost

Ask a shop owner what their average drill costs per hole and you'll usually get a blank stare or a rough guess based on the purchase price. What you almost never get is a number that accounts for reconditioning cycles, edge count, and the distribution of costs across the drill's full useful life. That information gap is expensive — it means replacement decisions are made on gut feel rather than data, and gut feel usually errs on the side of replacing too late (running drills past useful life) or too early (throwing away drills that had multiple productive regrinds left).

A drill reconditioning log closes that gap. It takes about 15 minutes to design, runs on a spreadsheet, and pays for the setup time within the first month. Here's how to build one that actually gets used.

The Log Structure: What to Track

Each row in your reconditioning log represents one drill through its life cycle. The columns you need:

• Drill ID: A unique identifier — engraved, marked with paint pen, or tagged. Without this, you can't track individual drills through multiple reconditioning cycles.
• Diameter and Grade: Size in decimal inches, material grade (M2, M35, cobalt, etc.), and original geometry (conventional or split point).
• Purchase Date and Cost: The starting point for cost-per-edge calculations.
• Reconditioning Events: Date sent out, date returned, cost charged, and post-regrind diameter (each regrind removes a small amount of material — tracking diameter over time shows how much life remains).
• Hole Count: How many holes between each reconditioning event. This is the key productivity metric. A drill producing 300 holes per regrind is twice as valuable as one producing 150 — and if both are the same grade, the difference is probably setup or application, not the drill itself.
• Failure Mode: When a drill finally goes to scrap, record why — normal wear-out after N cycles, breakage from X cause, or dimensional retirement (diameter too small for application after multiple regrinds).

That's the minimum viable log. You can add machine assignment, material being drilled, and operator notes, but start simple and add complexity only if the basic system proves useful.

Calculating Cost Per Edge

Cost per edge is the most useful number your log produces. It normalizes across different drill prices and reconditioning frequencies, giving you a single comparable metric across your drill inventory.

Formula: Total cost per edge = (Purchase price + Sum of all reconditioning costs) / Total number of edges used. Each regrind restores one edge, so a drill that was purchased for $15, resharpened 7 times at $3.50 each, and then retired, used 8 edges total at a total cost of $15 + $24.50 = $39.50. Cost per edge: $4.94.

Compare that to a drill that was purchased for $15, run to failure after one use, and discarded. Cost per edge: $15. The logged drill delivered three times the value per edge. That's not a subtle difference — it's the difference between a drill program that pays for itself and one that's a significant ongoing cost center.

Use cost per edge to benchmark reconditioning vendors and to identify problem areas. If one diameter consistently shows high cost per edge (few holes per regrind, high failure rate), investigate the application — wrong speed/feed, wrong geometry for the material, or a setup problem that's stressing that drill size specifically.

Replacement Decision Framework

Not every drill should be reconditioned indefinitely. Define clear retirement criteria so the decision is made on data, not inconsistent judgment:

• Diameter retirement threshold: Each regrind removes typically 0.010 to 0.030 inches of drill length and a very small amount of diameter. Define a minimum usable diameter for each application — typically the diameter at which the drill would produce an undersized hole for the largest tolerance class you need to hold.
• Maximum reconditioning count: After 8 to 10 full regrinds, the drill body has often been shortened enough that flute depth is compromised near the tip, and the original heat treatment's temper may be slightly affected by cumulative thermal cycling. Most 3/8" and larger drills are worth 6 to 10 regrinds before geometric retirement.
• Damage criteria: Visible cracks, chipped lands, or core damage that can't be fully corrected in a regrind cycle. These drills go to scrap regardless of hole count — the risk of failure in the cut is not worth the reconditioning cost.