Cost Estimating & Quoting for Contract Deep Hole Drilling

Getting five quotes for the same deep hole drilling job can yield five wildly different figures. The difference is not price gouging — it is the absence of a standard cost model for an operation where drill wander, coolant pressure, and tool regrind frequency can each swing the final price by 50% in either direction.

Cost estimating for contract deep hole drilling is fundamentally different from standard machining estimating. The specialised equipment, high coolant pressures, tool wear characteristics, and secondary operations unique to deep hole drilling require a purpose-built framework. This article provides a practical cost model with worked examples for both BTA and gun drilling operations.

Cost Components of Deep Hole Drilling ​

The total cost per part for deep hole drilling breaks into five independent components:

Part Cost = Material + (Setup ÷ Batch) + (Burden Rate × Cycle Time) + Tooling + Secondary Operations

Each component is independently estimable, and the framework allows the estimator to identify which cost drivers dominate for a given job.

Cost Component Breakdown ​

The burden rate multiplied by cycle time is nearly always the largest single cost driver for deep hole drilling, making accurate time estimation the most important skill in quoting.

Machine Burden Rates ​

The burden rate (machine hourly rate) captures all costs associated with operating the deep hole drilling machine for one hour.

Burden Rate Components ​

Typical Burden Rates by Machine Type ​

Burden Rate Calculation Example ​

For a CNC BTA drilling machine valued at $400,000:

However, most shops apply a multiplier of 2–3× the direct cost to cover profit, sales, and business overhead. The billed rate typically ranges from $120–$250/hr for this machine class.

Material Costs ​

Material cost for deep hole drilling must account for the raw material form and utilisation rate.

Material Forms ​

Material Cost Calculation ​

Material Cost = (Stock Weight × Material Price) / Utilisation Rate

Example — drilling a 25 mm bore through a 75 mm diameter steel bar, 500 mm long:

Tooling Costs ​

Tooling cost per part depends on tool type, purchase or regrind cost, and tool life in number of holes.

Gun Drilling Tooling ​

Gun drills are solid carbide tools that can be reground multiple times:

Tool life between regrinds depends on material and depth:

BTA Drilling Tooling ​

BTA tools use replaceable carbide inserts:

BTA tooling cost per hole is generally lower than gun drilling for equivalent diameters because only the inserts are replaced, not the entire tool body. However, the head body must be replaced after 500–2,000 holes depending on wear.

Setup and Programming ​

Setup Components ​

Total setup cost typically ranges from $750 to $4,650 depending on complexity.

Batch Size Impact ​

Setup cost per part = Total setup cost ÷ batch size:

For small batches (under 50 parts), setup cost is a significant portion of the total price. For production runs above 500 parts, setup becomes negligible.

Cycle Time Estimation ​

Cycle time estimation for deep hole drilling must account for the additional time from peck cycles.

Standard Drilling Time ​

Base drilling time for a single pass:

T_base = L / (f × n)

Where L = hole depth (mm), f = feed per revolution (mm/rev), n = spindle speed (rpm).

Peck Cycle Time Multiplier ​

The base time must be multiplied by a peck factor that accounts for retraction and approach moves:

Counter-intuitively, gun drilling and BTA drilling at very high depth ratios can have lower time multipliers than G83 peck drilling because they use continuous feed with through-tool chip evacuation.

Complete Cycle Time Formula ​

Total Cycle Time = T_base × Peck_Multiplier + T_approach + T_retract + T_coolant

Where:

• T_approach = time to rapid from start position to hole entrance (2–5 seconds typical)
• T_retract = rapid retract time at end of cycle (1–3 seconds)
• T_coolant = coolant-on dwell before cutting (2–4 seconds for high-pressure systems)

Cycle Time Example — Gun Drilling ​

10 mm diameter hole, 200 mm deep (20×D) in alloy steel:

Cycle Time Example — BTA Drilling ​

50 mm diameter hole, 500 mm deep (10×D) in alloy steel:

Quoting Framework ​

Complete Price Formula ​

Part Price = Material Cost
           + (Setup Cost / Batch Size)
           + (Burden Rate × Cycle Time)
           + Tool Cost per Part
           + Secondary Operation Cost
           + Markup (15–40%)

Worked Example — Gun Drilling Quote ​

Quote for 100 parts: 10 mm hole × 200 mm deep in alloy steel.

Worked Example — BTA Drilling Quote ​

Quote for 50 parts: 50 mm hole × 500 mm deep in alloy steel.

Factors That Increase Price ​

FAQ ​

How do I calculate the burden rate for a deep hole drilling machine? ​

Sum all annual costs associated with the machine (depreciation, floor space, maintenance, power, coolant, labour, support overhead) and divide by the available operating hours (typically 3,000–4,000 hours per year at 70–85% utilisation). Most shops then multiply this direct cost by 2–3× to arrive at the billed hourly rate, covering profit, sales, and general business overhead.

What is the typical hourly rate for contract deep hole drilling? ​

Rates vary by machine type and region. Manual gun drilling machines bill at $60–$100/hr, CNC gun drilling machines at $100–$180/hr, single-spindle BTA machines at $150–$250/hr, and multi-spindle BTA machines at $200–$350/hr. These rates include the operator, machine, coolant, and standard overhead but exclude material and special tooling.

How much does drill wander affect deep hole drilling cost? ​

Drill wander — the tendency of a deep drill to deviate from its intended axis — significantly affects cost. Industry standard is approximately 1 mm deviation per metre drilled. Correcting wander through slower feed rates, stiffer tooling, or secondary boring operations can increase cycle time by 20–50% and add inspection costs. Mitigation measures (starter bushings, guide pads, pre-drilled pilot holes) add setup cost but reduce per-part risk.

What is the most common cause of cost overruns in deep hole drilling? ​

Tool breakage at depth is the most expensive single failure mode — a broken BTA head or gun drill at 20× diameter can destroy the workpiece and require hours of extraction time. Underestimated peck cycle time is the second most common overrun. Many estimators use standard drilling time formulas without the peck multiplier (1.3–2.0× for deep holes), resulting in quotes that are 20–40% below actual cost.

How do I estimate tooling cost per hole for gun drilling? ​

Gun drill tooling cost per hole = (new tool cost / number of regrinds possible + regrind cost) / holes between regrinds. For example, a $200 gun drill with 6 regrinds at $60 each produces an amortised tool cost of ($200/6 + $60) = $93.33 per regrind cycle. If the tool drills 100 holes between regrinds, the tool cost per hole is $0.93.

When does honing become necessary and how much does it add? ​

Honing becomes necessary when the required surface finish is below Ra 0.8 µm or the tolerance is tighter than ±0.05 mm. Honing typically adds $5–$50 per hole depending on diameter, depth, and material. The cost multiplier for deep hole drilling plus honing is typically 1.3–2.0× compared to drilling alone.

What is the breakeven batch size for deep hole drilling? ​

Below 10–20 parts per batch, setup cost dominates and prices rise steeply for small quantities. Between 20–100 parts, setup amortisation becomes reasonable. Above 500 parts, setup becomes a negligible cost component and the price stabilises near the marginal production cost. For very large batches (10,000+), dedicated tooling and specialised workholding can further reduce per-part cost.

How do I factor coolant costs into a deep hole drilling quote? ​

High-pressure coolant system costs include the coolant concentrate ($15–$40 per gallon), water, filtration maintenance, and disposal. A typical deep hole drilling machine consumes $2–$8 per operating hour in coolant-related costs. For gun drilling with oil-based coolants, the cost is higher ($5–$12/hr) due to oil cost and mist collection. These costs are typically included in the machine burden rate rather than quoted separately.

Summary ​