When you’re considering buying a used / surplus / secondhand Doosan DNM 5700S (or equivalent DNM 5700 variant) CNC vertical machining center, there are common pitfalls that even seasoned buyers stumble into. Below is a structured guide (inspection checklist, gotchas, negotiation tips) to help you avoid expensive regrets.

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Know What “DNM 5700 / 5700S” Should Be / Typical Specs

Having reference benchmarks is critical — deviations aren’t always problems, but undocumented ones often are.

From published sources:

• The DNM 5700 (4th Gen) offers X / Y / Z travels of ~1,050 × 570 × 510 mm.
• Spindle: up to 12,000 RPM (in base models) with ~18.5 kW power.
• Tool changer: usually 30 tools (side-mounted) in many used listings.
• Work load on table: ~1,000 kg (for many 5700 variants) in specs.
• The “S” variant (DNM 5700S) is the high-speed version, with a spindle rated for 15,000 RPM in many catalogs.
• In user forums, people highlight lubrication (grease cartridges), way covers (especially Z axis cover folding) as recurring notes.
• Some reported issues: The through-spindle coolant (TSC) system in DNM 5700 machines may clog or lose prime due to check-valve blocks.
• A user reported that in a DNM 5700, Y-axis ball screw developed noise from misinstalled bearing housing, and later X & Y ball screws also had issues.

If the machine you inspect deviates wildly from these, demand explanations (e.g. retrofits, rebuilds) or assume risk.

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Common Pitfalls & What to Check to Avoid Them

Here are the major “gotchas” that tend to trap buyers, and how to spot or test for them.

Pitfall / Risk	What to Check / Test	Why It Matters / Red Flag
Spindle / Bearing wear or damage	– Runup test: ramp spindle from low to high RPM, listen/feel for noise, vibration, hum. – Use a test bar / dial indicator to measure radial runout, axial play. – Inspect spindle nose, taper, seals, housing for corrosion or damage. – Check whether the spindle chiller / oil jacket system still functions.	Spindle failures or bearing replacements are extremely expensive. Excessive runout or noise often means the spindle is near end-of-life.
Ball screws / axis drive issues / backlash	– Command axis moves (X, Y, Z), reverse direction and check backlash. – Jog axes and listen for binding or jerkiness. – Measure repeatability: repeatedly command a point and measure spread. – Inspect ends of ball screws for wear, end bearings, nut play.	Worn screws or nuts reduce accuracy and may require full regrinding or replacement.
Way / guide damage / chips intrusion	– Remove (or lift) way covers where possible and inspect underlying guides for scoring, pitting, scratches. – Check way covers, wipers, bellows, scrapers — are they intact or torn? – Look for uneven wear across ways (indicates misalignment or side-loads).	Damaged guides degrade machine geometry, leading to parts out-of-tolerance. Poor protection accelerates wear.
Lubrication & grease system failure	– Check the grease / lube cartridge system: is it functioning, is grease flowing? – Inspect lube lines, pumps, reservoirs, filters for clogging or contamination. – Ask when lube system was serviced or replaced.	Without proper lubrication, wear accelerates. A failed lube system leads to long-term catastrophic damage.
Tool changer / ATC faults	– Command a series of tool changes and watch for hesitation, mis-index, tool slip. – Inspect magazine arms, gripper, guide rails, indexing mechanism for play or damage. – Try heavy / long tools and small tools to stress extremes.	ATC failures or mis-indexing is a frequent cause of downtime; repairing or replacing ATC hardware is costly.
Control / electronics / drives issues	– Power up machine; review error logs, alarms, I/O module errors. – Inspect wiring, connectors, junction boxes for heat damage, corrosion, aftermarket splices. – Test digital I/O, limit switches, home switches. – Test servo drives / amplifiers for indication of fault codes.	Faulty electronics or proprietary control modules with no support can cripple the machine.
Through-spindle coolant (TSC) / coolant / check-valve problems	– Test TSC: does coolant flow reliably at rated pressure? If not, check valve blocks, filters, check valves (they often clog) – Inspect the TSC valve block, check-valves, pressure gauges. – Run the spindle with coolant on and see whether flow is stable.	Coolant system problems are common and, if unresolvable, may reduce the machine’s usefulness for many jobs.
Z-axis way cover collapse or damage	– In forums, users often mention the Z-axis way cover “folding like a beer can.” – Try moving the Z axis fully up and down while observing the cover; see if it binds or collapses. – Inspect the cover for dents, cracks, misalignment.	A failed or damaged cover lets chips / coolant penetrate into critical guides and screws.
Past crash / damage / repairs	– Ask seller: has the machine ever crashed an axis, overtravel, or been in accident? – Inspect machine base, casting, components for weld repairs, patched parts. – Check whether alignments have been corrected via shims or modifications (may hide damage).	Hidden structural damage undermines precision, and “repairs” may not restore original geometry.
Parts / support obsolescence	– Confirm availability of spare parts: spindles, screws, drives, ATC parts, control modules. – Ask whether the specific control version is still supported. – Check whether there are third-party suppliers or rebuilders for DNM / Doosan / DN Solutions. – Ask seller whether spare modules, wiring harnesses, or consumables come with machine.	If you can’t get spares, even a machine in good shape might become a liability.
Environmental / foundation issues	– Inspect whether the current installation was on a stable base, well leveled, with minimal vibration or contamination. – Look for signs of misleveling, base settling, or rust / corrosion from coolant exposure. – Evaluate how it will be rigged, moved, and re-leveled in your shop (floor layout, crane capacity).	Machines moved without proper re-leveling or foundation settling often lose geometry or alignment.

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Inspection / Testing Checklist for a DNM 5700S

Here’s a suggested order and method when you go to inspect:

1. Documentation & photos
   • Request logs, part replacement history, control backups, approvals
   • Inspect pictures of internal guts (guides, screws, cabinet internals)
2. Visual walk-around
   • Frame, base, cover panels, guards, enclosures
   • Way covers, bellows, scrapers
   • Control cabinet, wiring, junction boxes
   • ATC / magazine, gripper arms, guide rails
3. Power-up & control health
   • Boot CNC, scan for alarms, fault codes, I/O errors
   • Check control responsiveness, keys, touch screen (if any)
   • Inspect wiring and connectors for discoloration or damage
4. Motion / axis test (no load)
   • Jog X, Y, Z axes; command reversals and check for binding, jerkiness
   • Command repeatability cycles: same point multiple times
   • Check backlash by reversing small moves
5. Spindle run-up & test
   • Spin spindle from low to rated rpm
   • Listen for abnormal sounds, vibration
   • Check runout via dial indicator
   • Activate TSC (if present) and verify coolant flow and pressure
6. Load / cut test (if possible)
   • Run a simple machining pass; measure the part and check if within tolerance
   • Observe machine behavior, sloppiness, drift after repeats
   • Monitor coolant, chip evacuation, machine sound
7. ATC / Tool change test
   • Cycle tools repeatedly
   • Test extremes (heavy, light tools)
   • Observe magazine behavior, indexing, grip/release
8. Check auxiliary systems
   • Grease / lube system: verify grease flow and timing
   • Coolant pumps, filtration, chiller
   • Chip conveyor, enclosure seals, door movement
9. Measurement / precision checks
   • Backlash, repeatability, straightness, flatness, alignment
   • Spindle runout, tool change accuracy
   • Compare to reference specs
10. Final assessment & margin / discount negotiations
    • List all issues and estimate repair costs
    • Validate that machine can be aligned and calibrated to your tolerances
    • Get quotes for missing parts or retrofits
    • Use observed defects as negotiation leverage (discounts, parts, acceptance window)

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How to Position Yourself to Avoid Regret / Make Smart Bid

• Demand a conditional acceptance period (e.g. 30 days of test usage) if your contract allows, so post-installation issues can be addressed.
• Ask seller to include a “spare parts kit” (grease cartridges, filters, cables, seals) as part of the deal.
• Build in a healthy contingency margin (e.g. 15–25 %) for hidden wear or surprises you didn’t spot.
• Require the seller to run a baseline calibration test (e.g. cutting a known test piece) so you have proof of performance before purchase.
• Transport & rigging risks matter — plan crate / disassembly procedures carefully to avoid damaging guideways or components during move.
• Consider retrofitting / upgrade paths (e.g. replacing control modules, adding probe systems) and check feasibility early.