The cost of drilling a hole seems simple: you buy a bit, you use it until it's dull, you throw it out and buy another one. In reality, that accounting misses most of what determines your actual cost. Machine time, operator time, scrap rate, and service cycle decisions all factor in — and when you add them up, the numbers often look different than what shops expect.
Here's how to build a real cost-per-hole calculation and where the levers actually are.
The Components of Drilling Cost
Every hole has four cost components:
- Tool cost per hole: The purchase price of the drill (or regrind cost) divided by the number of holes it produces in its service life.
- Machine time cost: The cost of running your spindle, including overhead, for the time it takes to make the hole — including any approach, pecking, retract, and dwell.
- Scrap and rework cost: The amortized cost of rejected parts caused by drill performance issues, divided across the holes that produced them.
- Tooling management overhead: The time to track, pull, send out, receive, and return tooling to service — divided across the holes a tool produces in its lifetime.
Most shops only track item 1. Items 2, 3, and 4 are often larger.
Building the Tool Cost Calculation
Take a 3/8" HSS jobber drill as a simple example:
At this level, the cost-per-hole is roughly equal. But that's before the machine time factor.
Machine Time Is Usually the Bigger Number
A shop running a CNC machining center at $85/hour fully burdened (machine amortization, power, coolant, overhead) costs about $1.42 per minute at the spindle. A dull drill running at half the feed rate it should because nobody pulled it adds cycle time directly. On a part with 20 holes that takes 15 seconds each when the drill is sharp — but 30 seconds each when it's dull — you're adding 5 minutes of cycle time per part.
That's $710 in cycle time cost to avoid a $3.50 regrind. This is where the real economics of keeping tooling sharp live — not in the tool cost, but in what dull tooling costs you in spindle time.
The Scrap Factor
A worn drill is an out-of-tolerance drill. Holes go oversize as the lip height becomes asymmetric. Surface finish degrades. Breakthrough burrs increase. In close-tolerance work, a dull drill can produce scrap rates of 5–15% in holes that should be running clean.
If your part cost is $200 in material and labor and a dull tool causes one scrap per 20 parts, that's $10 per part in amortized scrap cost — completely avoidable by pulling the drill at the right interval.
Where to Move the Needle
Based on this framework, the decisions that change your drilling economics most significantly are:
1. Service interval discipline. Pulling drills before they're so dull they affect cycle time and quality is worth more than any tooling upgrade. The interval doesn't have to be perfect — it has to be consistent and conservative enough that dull tools don't reach the spindle.
2. Feed/speed correctness. Running at the right parameters keeps the drill sharp longer and makes each hole faster. A 3/8" HSS drill in 1018 steel should be running around 1,200 RPM at .007–.010" per revolution feed. Running too slow generates rubbing instead of cutting and accelerates edge wear without improving anything.
3. Tool quality matched to the application. A $4.50 economy drill and an $8.00 quality drill have similar tool costs per hole. But the quality drill regrinds well and produces consistent geometry across multiple cycles. The economy drill often can't. For any production application, quality tooling with a regrind program dominates over cheap tooling replaced on failure.
4. Regrind cost per cycle. If your regrind program costs $8 per drill to access and the drill is worth $4, you're spending more than the tool is worth. Mail-in resharpening services with flat per-size pricing make the regrind economics work for shops that can't justify an in-house grinder.
The practical conclusion is almost always the same: the cost of drilling is dominated by machine time and scrap, not tool cost. Keeping tools sharp at a reasonable service interval, running correct parameters, and having a cost-effective resharpen path pays multiples compared to any savings from cheaper tooling or deferred maintenance.