Deep Hole Drilling Cost Factors and RFQ
Deep hole drilling quotes vary far more than the process seems to justify — the same hole can be quoted two or three times differently by reputable shops. The reason is usually not that one vendor is expensive and another cheap. It is that deep hole drilling cost is driven by a few factors buyers rarely specify precisely, and vendors quote on different bases. This guide covers what actually drives the cost (qualitatively — prices vary too much by region to quote numbers), what to put in an RFQ, and how to compare bids fairly.
What Drives Deep Hole Drilling Cost
| Cost driver | Impact | What to specify in the RFQ |
|---|---|---|
| Depth-to-diameter ratio (L/D) | Highest — determines machine class, tooling, and cycle time | Depth and diameter, and your required L/D |
| Diameter | High — small bores need high-pressure machines and small drills; large bores need BTA or trepanning and more power | Exact diameter and tolerance |
| Material and hardness condition | High — annealed, prehardened, and hardened steel drill at very different speeds | Grade, condition, and hardness (e.g., 4140HT, 28–35 HRC) |
| Tolerance and finish | Medium–high — tight specs force lower feeds and secondary operations | Size tolerance, straightness, surface finish |
| Quantity and volume | Medium — setup is amortized; multi-spindle changes the unit cost | Quantity, run size, and repeat frequency |
| Machine class | Medium — dedicated machine vs retrofit vs manual lathe | State the machine class you expect, or let the vendor propose |
| Lead time | Low–medium — scheduling slack lowers cost | Required delivery date |
For the process economics with actual figures, see the gun drilling cost guide and the cost per hole analysis.
Why the Same Hole Gets Different Quotes
Before asking why quotes differ, check whether they are quoted on the same basis:
| Source of variation | What to watch for |
|---|---|
| Pricing basis | Per hole, per meter, or per run — with setup itemized or included |
| Depth ratio claims | Advertised versus practical production ratio (see depth limits by method) |
| Tooling and regrind | Included, itemized, or passed on separately |
| Material assumption | Annealed vs prehardened stock at the vendor’s default |
| Machine assumption | Dedicated machine vs retrofit — a retrofit quote is lower but depth-limited |
The fix is a precise RFQ and an explicit quoting basis.
How to Write a Deep Hole Drilling RFQ
A complete deep hole drilling RFQ specifies the part, not the price. Minimum content:
- Hole specification — diameter, depth, through or blind, entry/exit conditions (pilot, chamfer, existing bore)
- Tolerances — size tolerance, straightness, surface finish, concentricity where relevant
- Material — grade, condition, hardness range, stock form and OD
- Quantity — total, per-run, repeat schedule, whether samples are needed first
- Machine class — which machine class you expect, or “propose”
- Coolant and tooling policy — who supplies tooling, regrind expectations
- Logistics — inspection report/certs required, packaging, delivery date
A short spec block example:
Deep hole drilling RFQ
Hole: Ø12 mm through, 480 mm deep (40:1)
Tolerance: +0.05/-0.00 mm, straightness 0.08 mm/300 mm
Finish: Ra 0.8 µm as-drilled
Material: 4140HT, 28-35 HRC, Ø30 mm bar, 60 pieces
Entry: flat-bottom pilot per vendor spec
Run: 60 now, 60/month repeat
Machine: propose (gun drilling preferred)
Basis: quote per piece + setup, tooling and regrind itemized
Inspection: dimensional report per batch; certs if required
What to Ask Vendors Beyond the Spec
- Machine and stroke — verify the quoted depth is within the machine’s practical range, not just the advertised maximum.
- Quoting basis — per piece, per meter, or per run, and whether setup is separate.
- Tooling and regrind — who owns the tool, and how regrind is billed.
- First article — is a sample part available before the full run?
- Inspection — what report or certificate comes with the batch?
- Depth claim — ask for the practical production ratio, not the marketing number.
Comparing Quotes Fairly
- Normalize to one basis — convert every quote to per-piece plus setup before comparing.
- Give every vendor the same spec sheet — quoting from verbal descriptions produces incomparable bids.
- Watch the low ball — an unrealistic depth ratio, excluded setup, or bare tooling often hides the difference.
- Total cost, not quote cost — add setup, tooling, regrind, inspection, freight, and scrap risk before judging.
When to Choose Which Method (Cost Position)
Cost follows capability, so method choice positions the price more than the vendor does:
| Situation | Method that usually wins on cost |
|---|---|
| Small, deep, precise holes | Gun drilling |
| Large bores in high volume | BTA (single-tube) drilling |
| Adding deep hole capability to an existing CNC lathe | Ejector drilling retrofit |
| Very large diameters where a core is retained | Trepanning |
| Short holes below ~10×D | Twist or extended-length carbide drilling |
For the full logic, see the method comparison and the method selection calculator.
FAQ
Why is the same deep hole quoted so differently? Vendors quote on different bases (per hole vs per meter vs per run), assume different material conditions and machine classes, and advertise depth ratios that are not practical production numbers. A precise RFQ fixes most of the spread.
What makes a deep hole drilling RFQ complete? Hole spec (diameter, depth, through/blind, entry), tolerances, material grade and hardness, quantity and run size, machine class, tooling policy, and required certifications.
Should I ask for per-hole or per-meter pricing? Ask for the same basis from all vendors — usually per piece plus setup — so bids are comparable. Per-meter pricing hides setup and tooling.
How do I know a vendor’s depth ratio is realistic? Compare the quoted ratio against the practical production ranges in the depth limits guide, and ask what machine and stroke the quote assumes.
Summary
Deep hole drilling cost is dominated by a handful of factors — L/D, diameter, material condition, tolerance, volume, and machine class — and quotes diverge mainly because vendors price on different bases with different assumptions. A precise, complete RFQ plus a stated quoting basis turns a confusing spread of bids into comparable ones. When the numbers vary wildly, ask about the depth ratio, machine, tooling, and basis before assuming anyone is overpriced.
For the per-hole cost comparison across methods with figures, see method cost comparison. For selecting a gun drilling supplier, see how to choose a gun drilling service provider. For the method-level cost picture with figures, see the gun drilling cost guide.