A Test Run Is Not a Demo — It Is a Diagnosis
The seller starts the machine, the spindle turns, the axes move — "see, everything works." That is not a test run. That is a sales demonstration. A real test run is a systematic check of all machine functions under load, with parameter measurement and comparison against factory values.
As a procurement agent, Hutnia organizes test runs with mechanics for machines above 20,000 EUR. Below, we publish the program we use — so you know what to demand from your mechanic or from the seller.
Prerequisites — Before the Mechanic Touches the Machine
A test run only makes sense when three conditions are met:
- Machine is connected to power — sounds obvious, but during factory liquidations machines often stand disconnected. Demand connection at least 24 hours before your visit so the oil in the systems warms up.
- Machine is in automatic mode — not just manual mode (JOG). Many faults only reveal themselves during automatic movements at full speed.
- Documentation is available — operator manual, last service protocol, alarm list from the controller. Without documentation, the mechanic works blind.
Test run duration: Minimum 2 hours for machines up to 100,000 EUR. For machines above 100,000 EUR, at least 4 hours with a cooldown break.
Area 1: Warm-Up and Thermal Stabilization
The first phase is not a test — it is preparation. The machine must reach operating temperature.
Procedure:
1. Start the spindle at 50% of maximum RPM. Run for 15 minutes.
2. Increase to 75%. Run for 10 minutes.
3. Increase to 100%. Run for 5 minutes.
4. Measure spindle bearing housing temperature after warm-up.
Evaluation:
- Temperature below 50 degrees C after full warm-up — good condition
- 50-60 degrees C — acceptable but worth monitoring
- Above 60 degrees C — spindle bearings need attention
The mechanic should also check whether the machine shows excessive vibrations at full speed. Modern machining centers have built-in vibration sensors — have the reading displayed on the controller screen.
Area 2: Positioning and Repeatability
This test shows whether the machine hits the dimension — the most important criterion for production.
Procedure:
1. Mount a dial indicator on the table, probe against the stationary machine part.
2. Zero the indicator.
3. Program an X axis move of +100 mm and return to zero. Repeat 10 times.
4. Record the deviation at each return.
5. Repeat for Y and Z axes.
Reference values (per VDI/DGQ 3441):
- Repeatability up to 0.005 mm — factory condition
- 0.005-0.010 mm — good condition after years of operation
- 0.010-0.020 mm — acceptable for machining to IT8 tolerance
- Above 0.020 mm — problem with ball screw, guides, or controller
Important: Measure repeatability after warm-up. Cold readings may be better or worse and do not reflect production reality.
Area 3: Tool Changes
The automatic tool changer (ATC) is one of the most common failure sources in machining centers.
Procedure:
1. Load the magazine with at least 10 tool holders.
2. Program a change sequence: T1-T5-T3-T8-T1.
3. Execute the sequence 20 times.
4. Observe: change time, arm positioning, pull-in to the taper.
Red Flags:
- Change time more than 30% above manufacturer specification
- Tool does not enter the taper on the first attempt — worn gripper or finger
- Noise during the change — arm collision with the tool
- Controller alarm during the change — position sensor problem
ATC repairs cost 2,000-10,000 EUR. This is not something you "fix later."
Area 4: Test Cut
Now the real test — milling or turning a test workpiece.
The test workpiece should include:
- A face-milled surface at full tool width
- A pocket with corner radii
- Drilled holes (at least 3 diameters)
- A thread (if the machine has rigid tapping)
The mechanic measures:
- Flatness of the milled surface — within 0.01 mm over 100 mm
- Pocket dimensions — deviation from the program
- Hole diameters — comparison against programmed values
- Surface quality — roughness Ra (visual or with profilometer)
If the seller refuses a test cut, that is a serious red flag. Read our article about situations when the seller refuses a test run.
Area 5: Coolant and Lubrication
Auxiliary systems are often neglected, but their failure stops production.
Checklist:
- Coolant pump runs in all modes (external, through-spindle coolant / TSC)
- Through-spindle coolant pressure: minimum 20 bar (check the gauge)
- Central lubrication: all lubrication points receive oil (check visually at guides)
- Coolant filter: cartridge condition, date of last change
- Chip evacuation: chip conveyor runs without jamming
Area 6: Controller and Alarms
The last area — but equally important.
Procedure:
1. Access the alarm history. Every controller (Fanuc, Siemens, Heidenhain) has this function.
2. Review the last 50-100 alarms. Look for recurring codes.
3. Check the operating hour counters for spindle and machine.
4. Verify the controller software version — is it current, does the manufacturer still support it?
Red Flags in the alarm history:
- Recurring axis alarms (servo alarm) — drive or encoder problem
- Overheating alarms — cooling system defective
- ATC alarms — tool changer prone to faults
- Cleared alarm history — the seller is hiding something
At Hutnia, we demand the complete alarm history before every purchase recommendation. If the seller refuses, we advise against the purchase.
After the test run, the mechanic should deliver a written report with measurement results and a condition assessment. This report is your negotiation card — and your insurance when the machine arrives at your facility.
Before scheduling a test run, make sure the machine has passed the preliminary checks: spindle inspection and geometry check. This saves mechanic time and your money.
Book an initial consultation Step 0 for 49 EUR — fully deductible from the 500 EUR mandate. Schedule now
