Should you buy a $200,000 gundrill machine and drill in-house, or pay a contract shop per piece? The answer is not engineering — it is arithmetic. Volume, utilization, hidden costs, and risk tolerance decide. This guide walks through a four-lens decision framework, a fully worked break-even model, and the supplier-selection criteria that turn outsourcing into a competitive weapon rather than a gamble.
No single factor is decisive — the correct choice emerges when all four lenses agree. When they conflict, the conflict itself tells you where the risk lives.
Is deep hole drilling a core competency that differentiates your product (firearms, hydraulic systems, landing gear)? If yes, in-house protects the process knowledge that makes the hole good. If drilling is a supporting operation, outsourcing cuts management complexity.
Model the full cost over a 3–5 year horizon. In-house: capital, tooling, labor, coolant and filtration, maintenance, overhead. Buy: piece price, freight, minimum order quantities, incoming inspection. One-time payback math rarely survives contact with utilization reality.
At 40% machine utilization, added volume costs little; at 90%, outsourcing avoids a second machine purchase. And do you own the expertise to process titanium or Inconel, or hold ±0.002 mm? If not, a specialist shop already owns that learning curve.
A single supplier is a supply-chain risk; a single internal machine is a production risk. Lead time on the buy side is queue plus shipping; on the make side it is your own queue. For critical components, many manufacturers run dual sources — one internal, one external.
Build two columns, not two guesses. This baseline cost skeleton is used in the worked example below.
| Cost Factor | Make (In-House) | Buy (Outsource) |
|---|---|---|
| Equipment | $150,000–$500,000 (gundrill/BTA machine); $40k–$130k for entry or multi-spindle CNC | $0 (covered by supplier) |
| Tooling (annual) | $15,000–$40,000 | Included in piece price |
| Labor (annual, per operator) | $55,000–$75,000 | $0 |
| Coolant & Filtration (annual) | $8,000–$20,000 | $0 |
| Quality Inspection (annual) | $5,000–$15,000 | $3,000–$10,000 (incoming) |
| Freight & Logistics (annual) | $0 (internal) | $5,000–$20,000 |
| Minimum Order Quantity | None (drill as needed) | 50–500 pieces typical |
| Supplier Price per Piece | N/A | $2–$50 (depends on complexity) |
| Unit Cost at 1,000 pcs/yr | $35–$80 | $5–$60 |
Volume is the master variable. Below break-even, buying is cheaper because you pay only for the holes actually drilled. Above break-even, making wins because fixed cost spreads across more parts.
| Batch Size | Recommended Approach | Typical Lead Time |
|---|---|---|
| 1–10 pieces | In-house or quick-turn supplier | 1–5 days |
| 10–100 pieces | Evaluate both (supplier may specialize) | 1–3 weeks |
| 100–1,000 pieces | Supplier (if not core competency) | 2–6 weeks |
| 1,000–5,000 pieces | Supplier, or in-house if machine available | 4–10 weeks |
| 5,000+ pieces | In-house investment justified | Ongoing production |
Part: a mid-complexity hydraulic component — a 25 mm × 500 mm gun-drilled bore in 4140 steel — with annual demand uncertain between 2,000 and 15,000 pieces. Here is the arithmetic you would run before spending a dollar.
Gundrill machine $200,000, straight-line depreciated over 10 years → $20,000/yr of equipment cost.
Tooling $20,000 + one operator $60,000 + coolant and filtration $10,000 + in-house inspection $10,000 = $100,000/yr.
Fixed total $120,000/yr. Marginal cost per piece ≈ $2 (power, minor consumables) — nearly free once the machine is running.
Supplier piece price $15 (midpoint of the $2–$50 contract range), freight $10,000/yr, incoming inspection plus supplier management $5,000/yr.
Set make = buy: 120,000 + 2Q = 15,000 + 15Q → 13Q = 105,000 → Q ≈ 8,100 pieces/yr.
At 2,000/yr buying costs $45,000 vs $124,000 in-house. At 15,000/yr in-house costs $150,000 vs $240,000 bought. The crossover lands at ≈8,100 pieces/yr — squarely inside the 5,000–10,000 rule of thumb for justifying machine investment.
Both paths carry costs that never appear on the invoice. The make-or-buy decision lives or dies on these.
Contract shops compete on capability you would otherwise have to build. Representative ranges from real suppliers.
| Category | What to Verify |
|---|---|
| Technical Capability | Machine types (gundrill, BTA, EDM), max depth, min/max diameter, straightness capability, surface finish range |
| Quality Certifications | AS9100 (aerospace), ISO 13485 (medical), IATF 16949 (automotive), or ISO 9001 as baseline |
| Capacity | Number of machines, shift utilization, typical lead time, rush-order capability |
| Inspection | CMM, air gauging, bore scoping, surface profilometry, straightness measurement methods |
| Material Experience | Proven history with your materials — 4140, Inconel, titanium, hardened alloys up to ~48 R/C |
| References | Contactable clients in your industry with similar work |
| Certifications | NADCAP (if required), ITAR compliance, export controls |
Evaluation is an audit, not a Google search. Walk these categories in order — and reject anyone who answers “how” with marketing language.
| Category | Evaluation Criteria |
|---|---|
| Machine inventory | Count and model of gundrill/BTA/ejector machines; spindle count (multi-spindle = throughput) |
| Depth & diameter envelope | Can they hold your L/D and min/max diameter with margin? A shop at its envelope will drift |
| Straightness & finish | Published straightness (0.001”/ft) and as-drilled Ra (0.4–0.8 μm) — and how they MEASURE it |
| Material experience | Ask for parts made in YOUR material at YOUR hardness — 48 R/C hardened alloy is not 1018 |
| Inspection equipment | CMM, air gauging, bore scoping, surface profilometry, and who owns the measurement standard |
| Certifications | AS9100 / ISO 13485 / IATF 16949 / ISO 9001; NADCAP if required; ITAR and DFARS if defense |
| Commercial terms | MOQ, piece price vs machine-hour rate, freight terms, rush capability, capacity at YOUR peak season |
Outsourcing trades control for capital. Price that trade consciously before you sign.
A complete deep hole RFQ package should include:
Most profitable shops run a hybrid — keep the drilling that defines the product, outsource the drilling that just fills a hole.
| Keep In-House | Outsource |
|---|---|
| Prototype and R&D drilling | High-volume standard parts |
| Proprietary designs | Secondary operations (honing, coating) |
| Mission-critical tolerances | Overflow capacity during demand spikes |
| Short-lead-time orders | Standard envelope work at list capability |