Buying a deep hole drilling machine is a capital decision you can only get right by starting from your parts — not the brochure. This guide walks the practical sequence: define the hole, pick the method, understand the machine families, pin the specs that matter, sanity-check prices, inspect used iron, and vet the supplier.
Machines are quoted to an envelope. Before you look at any spec sheet, answer four questions about the parts you actually make:
| Method | Diameter | Choose when |
|---|---|---|
| Gundrilling | Ø0.5–50 mm | Small bores, best straightness and finish, moderate volume |
| BTA (STS) | Ø20–500+ mm | Large bores, high metal removal, high volume, deep |
| Ejector (DTS) | Ø18–200 mm | Retrofit onto an existing lathe/MC, irregular part faces, lower volume |
| Retrofit vs new | — | Ejector retrofit rides on iron you own; a dedicated machine is a new purchase |
Deep hole drilling machines come in three configuration dimensions — and each changes the price and the fit:
| Configuration | What it is | Best for |
|---|---|---|
| Vertical gundrill (1–4 spindles) | Tool feeds down into a clamped part | Small-diameter bores, mold cooling holes, micro work (< Ø6 mm), tight floor space |
| Horizontal gundrill / BTA | Tool feeds along the axis of a horizontal bar or tube | The most common for larger, deeper bores — shafts, barrels, cylinders |
| Multi-spindle (2–16+) | Several drills run simultaneously | High-volume (tube sheets, pellet dies); each spindle multiplies output |
| Combination / multi-axis (3–6 axis) | Deep hole + milling on one platform | Mold & die one-hit machining |
Rotation mode matters too: tool rotates over a fixed workpiece, workpiece rotates over a fixed tool (best straightness on round bars), or both counter-rotate (highest precision). A fixed or counter-rotating tailstock is an option on many machines — specify it if straightness is critical.
Representative builders by scale: Mollart and Profidrill span micro to BTA (Ø0.5–400/500 mm, depths to 4–18 m); Tibo builds modular single-to-12-spindle systems; Zonjet and other Chinese builders offer single- and multi-spindle CNC gundrill/BTA machines at entry pricing. Match the builder to your depth, diameter and volume, not the brand name.
| Machine type | Typical new price | Best for |
|---|---|---|
| Entry CNC deep hole machine | $40k–$80k | Mold cooling holes, valve bodies, small-bore jobbing |
| Dedicated gundrill machine | $50k–$200k | Precision Ø1–50 mm bores, L/D to ~200:1 |
| Ejector retrofit (DTS) | $30k–$100k | Adding deep hole capability to an existing machine |
| BTA machine, entry–mid | $60k–$180k | Ø12–250 mm production bores |
| BTA production machine | $200k–$800k+ | High-volume, aerospace/oil & gas, counter-rotation |
For machines above ~$50k, hire an independent inspector ($1,000–$4,000) and run the machine under power with a test cut. A seller who refuses either is a red flag. Priority checks for a deep hole machine:
| System | What to check | Accept / walk-away |
|---|---|---|
| Spindle runout (test bar, two positions) | Indicate at the nose and ~6 in out | OK < 0.0002 in at nose; walk away > 0.0005 in |
| Spindle bearings | Run at low / mid / near-max speed; listen for grind & rumble | Smooth = OK; grinding/rumbling = repair $5k–$50k |
| Ball-screw backlash (each axis, 3 positions) | Indicator on axis reversal | OK < 0.0003 in; budget $3k–$12k/axis if > 0.001 in |
| Ways / guides | Uncover box ways; check for scoring/galling; listen for guide-block clicking | Scoring = recondition $5k–$20k+ |
| Coolant / TSC (the deep hole heart) | Drain tank for sludge; run pumps at full pressure; test filtration | Rancid/sludge = poor maintenance; TSC pump replacement $1.5k–$5k |
| Spindle hours | Compare to bearings’ ~10k–20k hr rating | High hours = budget for a rebuild |
Make final payment contingent on the machine passing defined tests in your facility — don’t accept on the seller’s floor alone.
Check foundation and leveling; flush and replace coolant and lubricants; power up and repeat the seller’s geometry checks.
Drill trial bores at production parameters — measure diameter, straightness, surface and cycle time against the spec. Run 10–20 cycles to catch thermal drift.
Record backlash, drift and accuracy as the acceptance baseline — this is what you compare against a year from now.
Give drawings, materials, target cycle time and L/D. Ask the vendor to propose a configuration and ROI estimate.
ISO 9001 / CE, and above all application engineers — deep hole drilling is process-experience-heavy.
Bore range, depth, spindle power, coolant pressure/flow, filtration, rotation mode, and acceptance test criteria (VDI 3212).
Regional service, spare parts lead time, operator training, and whether the machine can be automated later.
A trial part under production conditions — measured straightness, finish, cycle time and tool life — beats any brochure. Tie the trial result into the acceptance clause.