1) Machine Overview

The DOOSAN DNM 650 II is a high-performance CNC vertical machining center (VMC) engineered for precision, stability, and productivity. Manufactured in South Korea, it is widely recognized in toolmaking, aerospace, and general machining industries for its rigid construction, reliable spindle performance, and superior surface finish capability.

Its 8,000 rpm (standard) or optional 12,000 rpm spindle, coupled with a BT-40/50 taper, linear guideways, and advanced FANUC or Siemens control, make it a proven production-class machine for both medium and large components.

---

2) Key Technical Specifications to Verify

Component	Specification	What to Inspect
X/Y/Z Travel	1270 × 670 × 625 mm	Verify full travel limits and smooth movement on all axes.
Table Size	1460 × 670 mm	Check flatness with indicator; confirm no nicks or clamping scars.
Spindle Speed	8,000 rpm (std) / 12,000 rpm (opt.)	Run at multiple speeds; listen for bearing noise or imbalance.
Spindle Taper	BT-40 or BT-50	Measure runout and tool retention force.
Spindle Power	18.5 / 22 kW (25 / 30 HP)	Confirm continuous vs. peak rating; inspect drawbar tension.
Rapid Traverse	36 m/min (X/Y), 30 m/min (Z)	Verify at full stroke without abnormal vibration.
Tool Magazine	30 (40 opt.) ATC	Run tool-change test; check gripper arms and indexing time.
CNC Control	FANUC i-Series / Siemens 828D	Inspect screen, keys, soft buttons; check alarm log.

---

3) Structural Integrity and Foundation Check

• Column & Base Casting: Confirm no stress cracks or coolant-induced corrosion.
• Guideways: DNM 650 II uses roller linear guideways — inspect for preload consistency, abnormal backlash, or scored rails.
• Ball Screws: Check for axial play, uniform lubrication, and absence of metallic noise.
• Way Covers: Ensure no oil leakage or tears; protect from chip contamination.

---

4) Spindle & ATC Evaluation

Test	Method	Acceptable Result
Spindle Runout	Dial indicator on precision bar	≤ 0.003 mm
Spindle Temperature Rise (30 min @ 6,000 rpm)	IR thermometer	≤ 15 °C
Drawbar Force	Taper-specific gauge	≥ 70 % of OEM spec
ATC Cycle Time	Automatic tool-change test	≤ 3 seconds per cycle
Spindle Vibration	Accelerometer / analyzer	Smooth spectrum; no bearing peaks
Tool Seating	Blue test	Even contact on 80–90 % of taper surface

---

5) Axis Performance & Accuracy Verification

• Backlash Test: Jog reversal at 0.01 mm increments; should not exceed ±0.005 mm.
• Laser Interferometer Test: Verify positioning error ≤ ±0.005 mm per 300 mm.
• Ballbar Circularity: Perform at 100 mm and 300 mm radius — should achieve ≤ 0.02 mm deviation.
• Rapid Traverse Stability: Observe acceleration / deceleration sound; ensure no oscillation.
• Z-Axis Counterbalance: Run servo trace; confirm stable load during up/down motion.

---

6) CNC Control & Electrical Systems

• Check CNC boot-up time, communication ports (Ethernet, USB, RS232), and I/O signals.
• Review alarm and servo error history; repeated axis overloads may indicate mechanical drag.
• Inspect servo amplifiers, fans, and heat exchangers for dust or overheating.
• Verify backup batteries, parameter files, and ladder logic version.
• Ensure the control cabinet is dry, clean, and properly grounded.

---

7) Lubrication, Hydraulics & Coolant

System	Checkpoint	What to Look For
Central Lubrication	Oil level, distribution block	Continuous flow to each guideway; no leaks or dry lines.
Hydraulics (ATC / Clamping)	Pressure gauge, valves	Stable pressure, no foaming, and clean return lines.
Coolant Tank	Filter & pump	Clear coolant, no metallic chips, odor, or biological growth.
Air Supply	FRL unit	Dry, regulated air between 6–8 bar; drain water traps.

---

8) Inspection Steps (Step-by-Step Procedure)

A. Static Evaluation

• Power off; inspect alignment and general cleanliness.
• Use precision level to confirm machine is not twisted.
• Check for paint blistering — often indicates oil or coolant seepage from castings.

B. Functional Test

1. Power up control and warm up axes for 30 minutes.
2. Home all axes and check for repeatable reference position.
3. Execute manual feed at 25 %, 50 %, 100 % rapid to detect resonance.
4. Run spindle from low to high RPMs; listen for bearing noise.
5. Run ATC cycle 10 × continuously; ensure error-free operation.

C. Accuracy Verification

• Conduct laser calibration along X/Y/Z.
• Measure orthogonality (squareness) using a granite square or ballbar — tolerance ≤ 0.02 mm over full travel.
• Perform face-milling test on a 200 × 200 mm plate; check step marks and parallelism.

---

9) Common Wear or Failure Signs

• Spindle bearing noise or temperature rise after 15 min.
• ATC arm mis-timing or slow pocket indexing.
• Linear guide scoring or discoloration (lack of lubrication).
• Ball screw thrust bearing play, visible in reversal backlash.
• Coolant leaks inside column or under base (seal failure).
• Axis servo errors during homing or feed moves.

---

10) Required Documentation

Document	Importance
OEM specification & parameter sheet	Confirms exact build configuration
Geometry & laser test reports	Proof of positioning accuracy
Maintenance records	Validates lubrication & service frequency
Electrical and hydraulic schematics	Essential for troubleshooting
Tool list & manuals	Verify included tooling and accessories
Spindle overhaul or bearing replacement certificates	Key to determining spindle life expectancy

---

11) Acceptance Criteria Summary

Parameter	Target Value	Note
Positioning Accuracy	±0.005 mm / 300 mm	Measured by laser
Repeatability	±0.002 mm	Bidirectional test
Ballbar Circularity	≤ 0.02 mm	100 mm radius
Spindle Runout	≤ 0.003 mm	At taper gauge
Surface Finish	Ra ≤ 0.4 µm	200 × 200 mm test face
Thermal Drift (2 hr)	≤ 5 µm	Warm-up before testing
Tool Change Time	≤ 3 s	Continuous 20 × test
Noise Level	< 75 dB (A)	Under load

---

12) Value-Adding Features That Increase Worth

• Upgraded 12,000 rpm direct-drive spindle
• Heidenhain or Renishaw probing system installed
• Chip conveyor and through-spindle coolant (TSC)
• 30+1 or 40+1 ATC magazine
• Full maintenance logbooks and calibration reports
• Retrofitted energy-efficient servo drives or inverter coolant pumps

---

13) Red Flags — Avoid Purchase If

• Repeated servo amplifier faults or untraceable parameter corruption
• Z-axis drift or failure to hold position when power off
• Cracked casting on column or base
• Missing spindle chiller in high-speed configuration
• Thermal compensation disabled or uncalibrated scales
• Unknown control password lockout without OEM support

---

14) Buyer’s Quick Checklist

✅ Machine serial number & build year photo
✅ Spindle hours and service log verified
✅ Laser or ballbar report available
✅ Spindle & ATC test completed without alarms
✅ Way covers and guideways clean and lubricated
✅ Control keys, display, and emergency stop functional
✅ Coolant, air, and hydraulic systems leak-free
✅ All original manuals and tool holders included

---

Pro Tip

When buying a used DOOSAN DNM 650 II, prioritize units that were maintained under preventive service contracts and have recent geometry verification reports. Machines from aerospace or die-mold facilities often exhibit the best preservation of accuracy due to controlled environments and light-cutting operations.