DOOSAN DNM 350/5AX Spindle Repair after Severe Collision

Bybmsserwis

DOOSAN DNM 350/5AX Spindle Repair

  • Machine: 5-axis machining center DOOSAN DNM 350/5AX

  • Spindle: DOOSAN / FANUC

  • Speed: 15 000 rpm

  • Taper: BT40

A DOOSAN spindle arrived for service after a severe collision with the 5-axis table. The symptoms were clear: noisy bearings and high radial runout, which prevented stable machining. In this kind of machine everything is decided at very small values — every micron counts

From the start we agreed with the customer on a fast approach. After disassembly at the customer’s site, we collected the spindle directly, door-to-door to shorten downtime and avoid additional transport risk. The maintenance department on the customer’s side did a great job: quick decision, tidy workstation, complete incident information. Thanks to that we could get to work immediately.

Spindle repair — DOOSAN DNM 350/5AX

Why this repair
of the DOOSAN DNM 350/5AX spindle mattered

In 5-axis machining, even small spindle runout transfers to the tool and then to the part. You get vibrations, poorer surface finish, shorter tool life and repeatability issues.

At 15 000 rpm every deviation grows with speed, so precise repair is essential. In this case the spindle arrived straight after disassembly — freshly delivered from the customer to our service facility and secured for unloading and initial inspection.

After this direct delivery from the customer to the service, our goal was simple: restore quiet operation, stability and repeatability and prepare the spindle for re-installation, so the machine would again hold micron-level tolerances.

Spindle prepared for transport — DOOSAN DNM 350/5AX Safe spindle transport — DOOSAN DNM 350/5AX

How the spindle repair looked
DOOSAN DNM 350/5AX — step by step

1. Initial diagnostics and measurements
We started with full measurements: radial and axial runout, acoustic tests, vibration checks and a BT40 taper inspection. We verified spindle behavior up to the operating speed of 15 000 rpm. The collision effects were confirmed: worn bearings and taper surface damage.
2. Disassembly and thorough cleaning
We disassembled the spindle into subassemblies. Each part was cleaned in several stages: rinsing, ultrasonic bath, drying at controlled temperature. We removed all chips and contaminants that could remain after the collision. Cleanliness is crucial — contamination shortens the life of new bearings and increases vibration.
Disassembled and cleaned spindle components — DOOSAN DNM 350/5AX Spindle inspection and cleaning — DOOSAN DNM 350/5AX
3. Replacement of precision spindle bearings
We installed new precision bearings matched to this machine’s loads and speed. We ensured correct seating, clean housings and proper preload. As a result, the spindle runs stably without excessive heating and without the noise that had been audible even at low speed.
4. BT40 taper restoration
The taper showed marks from impact and wear. We measured the geometry and restored the taper profile to ensure repeatable, runout-free tool clamping. A proper taper gives secure tool holding, better surface finish and lower bearing load.
5. Assembly and settings
We reassembled the spindle, set the correct operating parameters (including clearance and preload) and checked axial alignment. Everything was done carefully with torque and temperature control. This reduces stress and extends the life of the entire unit.
6. Precise balancing
After assembly we performed dynamic balancing. At 15 000 rpm even a small unbalance causes vibration. After balancing the spindle ramps up smoothly and vibration drops to safe levels. This translates into better surface quality and lower tool wear.
Spindle service — balancing — DOOSAN DNM 350/5AX Spindle on a balancing machine — DOOSAN DNM 350/5AX
7. Final tests
We carried out warm-up, running-in, temperature control, noise and vibration measurements, and a repeat runout check. The results confirmed that the bearing noise disappeared and radial runout returned to reference values.

Spindle geometry setup
and axes in the DOOSAN DNM 350/5AX machine

Repair alone is not enough. After the spindle returned to the plant, the customer’s maintenance department performed geometry setup of the spindle and all machine axes. After installation they verified squareness and parallelism, set angles, corrected errors and applied necessary compensations. In a 5-axis machine this is crucial: only after such setup can you speak about a full return to accurate, repeatable work. After this procedure the machine again holds tolerances in the micron range — precisely HALF A MICRON — and machining is stable even on demanding toolpaths.

Clamping force measurement of the mounted spindle — DOOSAN DNM 350/5AX Mounted spindle runout measurement — DOOSAN DNM 350/5AX

Final result
DOOSAN DNM 350/5AX spindle repair

  • bearing noise disappeared,
  • radial runout dropped to reference values — exactly half a micron (0.0005 mm),
  • the BT40 taper provides secure and repeatable tool clamping,
  • 5-axis machining is stable at 15 000 rpm,
  • downtime was reduced thanks to fast pickup and good cooperation with maintenance.

We have provided a 12-month service warranty on the repaired spindle. This confirms the work is durable and ready for real production, not just dry tests.

Spindle runout measurement after balancing — DOOSAN DNM 350/5AX Spindle balancing — DOOSAN DNM 350/5AX

Summary
DOOSAN DNM 350/5AX spindle service

The DOOSAN/FANUC spindle in the DNM 350/5AX suffered a collision that caused loud bearing noise and high runout. We performed a complete repair: replacement of precision bearings, taper restoration, cleaning of all elements, assembly and balancing, followed by tests. On the customer side, the maintenance department set the geometry of the spindle and all axes, which completed the process. The machine returned to form and production is once again reliable and repeatable.

Spindle mounted in the machine — DOOSAN DNM 350/5AX

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