If you’re looking at buying a used DMG MORI DMU 50 (especially the 3rd-Generation / 5-axis version), there are a lot of things to check. These are precision multi-axis machining centers, so wear, maintenance history, and environment make a big difference. Below is a detailed guide to what you should pay attention to, what tests to ask for / do, red flags, and questions to ask.

---

What You Should Know First — Baseline Specs & What “Good” Looks Like

To evaluate condition, you need to know what the machine should be. Here are specs for the DMU 50 (3rd Generation / similar models) so you can compare what you’re inspecting against the ideal:

Spec	Typical / Published Value
X travel	~ 650 mm
Y travel	~ 520 mm
Z travel	~ 475 mm
Table diameter / work-clamp area	~ 630 mm
Maximum workpiece weight	~ 300 kg (≈ 660 lbs)
Spindle speed options	Standard ~ 15,000 rpm; optional up to ~ 20,000 rpm on higher spec models
Spindle taper / tool interface	Often HSK-63 in newer / high-speed configurations
Rapid traverse rates	~ 42 m/min in X, Y, Z in newer models
Tool magazine	Standard 30-pocket; optional 60 or 120 pockets in many listings

Knowing these lets you check whether the used machine still meets spec, or if some components have been downgraded or neglected.

---

What To Inspect / Test On-Site or Before Purchase

Because multi-axis machines have many wear or failure points, you should do a fairly thorough inspection and preferably see the machine running under load. Here are critical things to check:

Area	What To Inspect / Test	Why It Matters / What Common Problems Are
Spindle & Spindle Bearings	– Run the spindle at all speeds (low, mid, high); listen for noise, vibration, temperature rise. – Measure spindle run-out (both radial & axial) using test bar. – Inspect spindle taper / tool interface for wear / damage (chips, nicks, scoring). – Check spindle drive motor health: current draw, any overheating. – If many hours, ask if spindle bearings have been replaced.	Worn spindle bearings degrade surface finish, reduce precision, and make tool wear worse. Spindle taper damage causes misclamping, vibration. A spindle that overheats or draws too much current is a big repair cost.
Rotary / Swivel Axes (B & C-axes)	– Check B-axis swivel / tilt operation (speed, smoothness, backlash). – Check C-axis rotation, indexing accuracy. – Inspect limit switches / reference switches for axes; see if any alarms / lost references occur. – Look for signs of binding, stiff motion, or backlash.	These axes are often more lightly used but critical in 5-axis machines; misalignment or wear here will seriously degrade accuracy of multi-face and simultaneous 5-axis work. Users often report issues with limit / home switches, or with the B-axis brakes etc.
Guideways, Ball Screws, Linear Scales	– Move axes through full travel (X, Y, Z) and feel for binding, “soft spots”, uneven motion. – Inspect guide surfaces for scoring, pitting, rust; look under way covers. – Check ball screws for backlash and for smooth motion. – If linear scales (or direct measuring) are present (often they are in newer DMU 50s), check their calibration, condition, whether clean & free of damage.	Worn guideways or screws reduce precision, tolerances, can cause chatter. Linear scales are precision-enhancing; if damaged or miscalibrated, you lose responsiveness. Rust under covers can get bad before visible.
Control System / CNC, Electronics	– Identify control brand and version; is it Siemens, Heidenhain, or other? – Check firmware/software updates; compatibility; diagnostic / error history. – Inspect electronics cabinets: wiring, cleanliness, signs of overheating or moisture. – Check interface, pendant, display, buttons: are all working? Is there documentation/manuals? – Check if optional features/modules are working: probing, tool-measurement, high speed spindle, thru-spindle coolant etc.	Control issues often become expensive later. Missing or broken modules reduce functionality. If spare parts or software licenses are obsolete, repair can be slow or unsupported.
Tooling, Tool Changer, Tool Holders	– Test tool changer: pick up tool changes, speed, reliability. – Inspect tool holders: wear, coolant channels, clamping surfaces. – Check maximum tool length / diameter capability and whether those still achievable (has there been tool collision or damage?) – If thru-spindle coolant / high pressure coolant is used, check that lines are clean, seals intact.	Worn or damaged tools & holders degrade accuracy. Tool change issues cause downtime. High pressure coolant leaks cause damage.
Cooling, Thermal Control, Machine Bed / Base	– Inspect cooling systems: coolant pumps, filtration, coolant quality; whether cooling of spindle / axes is functioning. – Check that the bed/column structure is correct: no warping, cracks, or signs of shock or mechanical damage. – Watch the temperature of the machine and ambient conditions; see whether there are thermal drift problems. – Look at the one-piece bed etc (in newer DMU 50s) for structural integrity.	Thermal stability is critical in precision machining. Cracks or bending lead to misalignments. Coolant / filtration neglect leads to overheating or corrosion.
Rapid Motion / Feed Rates / Axis Speeds	– Test rapid traverse in all three axes; check for jerks, acceleration, deceleration. – Test combined motion moves (e.g. simultaneous 5-axis moves) if possible. – Observe motion smoothness especially in small moves / fine positioning.	Some older machines or worn drives will lose performance; jerky motion means worn components or poorly tuned parameters. Slow axis motion reduces throughput.
Table & Workholding / Table Load	– Check table flatness, condition: is it worn, scratched, damaged? – Check table load capacity (are bearings in table good? Any sag?) – Inspect rotary/swivel table, whether bearings are good and run smoothly. – Clamping system condition (fixture holes, clamps etc.)	If table sag or bearing wear, workpiece alignment suffers. Rotary table wear leads to rotational run-out errors. Workholding is often overlooked.
Overall Accuracy & Test Machining	– If possible, cut test parts that use the full travel / full work envelope. Measure positional accuracy, contouring, surface finish. – Repeat the same part to test repeatability. – Measure performance near extremes of travel (edges of envelope). – Warm-up the machine; see if the performance changes over time or after hours of operation.	This is the real test: specs are one thing, what the machine does under real load is what matters. Degradation frequently shows up at extremes or after warm-up.
Usage History & Maintenance Records	– Ask how many hours the machine has run (spindle, mains, idle etc.) – What sort of parts/materials were produced (hard alloys, continuous heavy cuts etc.) – Maintenance schedule: bearing changes, lubrication, way/guide maintenance, cooling system upkeep. – Any known defects or repairs (like crashes, spindle rebuilds, replacement of axes etc.) – Environment: shop floor conditions, dust, temperature swings, vibration etc.	Good maintenance is often the difference between a “cheap now” machine that’s expensive to operate vs one that performs well and is reliable. Harsh environment accelerates wear.
Spare Parts / Support / Software & Licenses	– Are spare parts (bearings, encoders, drive modules, tool holders etc.) available locally or regionally? – Is the OEM or reseller support still active for that model / control version? – Are software licenses, optional features, probing packages etc. transferable and included? – Are documents / manuals / calibration certificates available?	Sometimes the pump, encoder, spindle etc are expensive to replace. If support is discontinued, you may face long downtimes or high import costs.
Facility & Installation / Utilities	– Check power requirements / compatibility with your facility (voltage, phase, current). – Check foundation / floor condition; machine weight & if required anchoring. – Check for good cooling / air conditioning / cleanliness; shop environment. – Access for moving in/out, maintenance access, tool changes etc. – Check coolant disposal, chip removal, guarding etc.	Poor installation or utilities often reduce achievable performance. Moving / installing large machines is expensive, and misaligned machines often suffer early wear.

---

Known Issues / Common Weaknesses (from Users & Forums)

From what users have reported (and what comes up in forums), these are things that tend to come up on DMU 50 machines:

• B-axis issues with limit switches / references: Some DMU 50s have trouble finding the B-axis reference on startup. The limit or home/reference switch may be worn or misadjusted, causing crashes or errors.
• Brake problems: Brake units in rotary/swivel axes or table axes may be worn, over-tight, or not operating smoothly. This causes over-loads or axis alarm problems.
• Rails / guideways rust: Even small rust in the guide/rail grooves, especially where balls or linear motion components run, can become problematic quickly.
• Electrical / VFD / Drives overheating or being mis-wired: Some machines have been burned or had failures because of incorrect voltage or wiring (e.g. European vs other standard voltage mismatches) or insufficient cooling in the electrical cabinet.
• Spindle specs variation: Not all DMU 50s are created equal—spindle speed, power, taper may vary depending on the generation or optional high-speed spindle. It’s important to verify which spec you have.

---

Red Flags — When to Be Cautious or Walk Away

These are warning signs that either require serious discounting or may indicate the machine is not worth buying:

• Spindle with excessive run-out, noise, vibration, or overheating in “idle” speeds.
• B-axis or C-axis that fails to reference/homed properly, or errs out during setup or startup.
• Large backlash or loose/torn elements in rotary/swivel joints.
• Rust or corrosion on guide rails, especially under way covers; signs of water damage, coolant leaks.
• Electrical cabinet with signs of heat damage, burnt wires, corrosion, water ingress.
• Tool changer problems: stuck tools, slow or misaligned change operations.
• Missing critical accessories (probes, tool-length measurement, tables, fixtures) or replacement parts prohibitively expensive or unavailable.
• Control system or software versions that are outdated or unsupported; missing licenses or features you need.
• Wear in structural parts (bed, bridge, columns) indicating shocks or impact damage.
• Environment issues if the shop is dirty, temperature fluctuates heavily, or machine not on solid foundation.