Drill Performance Benchmarking: Tracking Holes Per Regrind

You cannot improve what you do not measure. Most shops have a general sense that "drills last about X holes" — but that sense is rarely based on actual data, and it hides enormous variability. Setting up a simple tracking system for holes per regrind turns drill performance from a vague feeling into a number you can manage, compare, and improve.

Why Holes Per Regrind Matters

Holes per regrind (HPR) is the fundamental efficiency metric for any drill reconditioning program. It tells you how much work you are getting from each sharpened drill before it needs service again. A higher HPR means less resharpening frequency, lower per-hole tool cost, and fewer tool changes per shift.

HPR also functions as a process health indicator. When HPR drops unexpectedly, something changed — material hardness, coolant concentration, spindle runout, operator behavior, or the sharpening quality itself. A tracking system gives you the baseline to notice the change and the context to diagnose the cause.

Setting Up the Tracking Sheet

The minimum viable tracking system requires five data points per drill event:

• Drill ID: a stamped or marked identifier that follows the drill through its service life
• Drill size and grade
• Date installed / date pulled
• Hole count: from machine counter or operator log
• Reason pulled: scheduled rotation, dull, chipped, broken, or other

This can be a paper log at the machine, a shared spreadsheet, or a simple entry in whatever ERP or tool management system your shop already uses. The key is that the data is captured at the machine, in real time, not reconstructed from memory at the end of the week.

After pulling the drill, add two more fields: was it resharpened or retired, and what was the resharpening cost. This completes the per-drill cost data you need to calculate true tooling cost per hole.

Establishing the Baseline

The first 30-60 drill pull events in your tracking system establish your baseline HPR. Do not try to optimize anything during this period — just collect data. Calculate the mean HPR, the standard deviation, and the range (highest to lowest). These three numbers describe your current process performance.

A high standard deviation relative to the mean indicates inconsistent process conditions — perhaps variable material hardness, inconsistent tool changes (some operators run drills longer than others), or variable sharpening quality. A narrow distribution indicates consistent conditions and consistent operator behavior.

The "reason pulled" field is particularly diagnostic during baseline collection. If 30% of your drills are being pulled for "broken" or "chipped" rather than "scheduled" or "dull," your tool life limits may be too aggressive, or there is a process instability causing premature failure. If nearly all drills come out dull rather than broken, your life limit is appropriately conservative.

Setting Improvement Targets

Improvement targets for HPR should be grounded in your baseline and adjusted for realistic gains. A 20% improvement in mean HPR is an achievable near-term target for most shops with no benchmarked program. A 50% improvement is possible but requires systematic process work — not just tighter discipline but actual changes to speeds, feeds, coolant, or sharpening geometry.

Do not set HPR improvement targets in isolation. HPR is only valuable if hole quality is maintained. A drill that runs 50% more holes by tolerating degraded geometry and producing out-of-tolerance holes is not an improvement — it is a quality problem. Track HPR alongside hole diameter variation and any quality rejections associated with drilling operations.

Comparing Vendors and Drill Grades

Once you have baseline data, you can run controlled comparisons. Want to know if M42 cobalt drills outlast M2 in your stainless application? Run 30 drills of each grade, tracking identical parameters, and compare the HPR distributions. The data answers the question objectively rather than relying on vendor claims or shop lore.

Similarly, comparing resharpening vendors: send identical dull drills to two different services, run each set under identical conditions, and compare the resulting HPR. Quality resharpening consistently produces higher post-grind HPR. If you are seeing wide variation between resharpened batches, the data will show it — and that gives you grounds to change vendors or establish quality requirements.

The investment in this tracking system is low — a few minutes per tool change and a simple spreadsheet. The return is an objective foundation for every tool management decision you make going forward.