The Fadal 4020 being considered is priced at about $2,000 delivered, and its reported X-axis fault followed a swap with the Y-axis power supply. That points toward the supply as a suspect, but the seller did not provide the specific fault or a completed repair test. Treat the machine as a project with a promising lead, then check the electrical path, mechanical condition, and operating functions before deciding.
What does the X-axis fault tell you about the request path?
An axis move begins as a command from the control, passes through the axis drive and its electrical connections to the motor, then becomes motion through the machine’s mechanical assembly. A fault can arise at any point along that path. The seller’s report that the fault moved when the X- and Y-axis power supplies were swapped is useful because it associates the symptom with a component moved during the test. It does not identify the exact failure mode or rule out a second fault.
Ask the seller what the control displayed, whether the fault occurred at power-up or during motion, and exactly what was swapped. Clarify whether the problem followed the supply itself, rather than a cable, connector, or other item moved at the same time. The 12 V DC supply attribution is the seller’s diagnosis; do not treat it as a confirmed repair until the machine runs X repeatedly without the fault returning.
| Observed result | What it suggests | Next check |
|---|---|---|
| Fault follows the swapped power supply | The supply is a leading suspect, assuming only the supply was exchanged and connections were restored correctly. | Test with a known-good compatible supply and repeat X-axis moves. |
| Fault stays with the X axis | The fault may be in the X-axis drive, cable, motor, control path, or mechanical load. | Inspect the X motor cable and conduit, then obtain the exact drive or control fault. |
| No specific fault is available | The diagnosis is incomplete; intermittent faults may disappear during a short inspection. | Ask for the fault indication and conditions that reproduce it before payment. |
What should you inspect before applying power?
Follow the physical path first: inspect the machine and its visible wiring before interpreting control messages. Look for damage to the cabinet, sheet metal, table, and accessible cables. The reported X-axis cable concern on older Fadals is a broken conduit that can cut the servo cable. Examine the conduit over its accessible length and inspect the cable where it enters or exits the conduit. A damaged outer cover can conceal conductor damage; a jog test alone does not clear the cable.
Check the table for drilled holes, dents, and visible abuse, and look for signs that the machine has been physically neglected. Ask how it was transported and whether components were removed or damaged. These checks do not establish geometric accuracy, but they identify obvious repair work and help decide whether a more detailed inspection is warranted.
Plan the move before purchase. The machine was described as roughly 10 tons, so confirm the actual machine weight and lifting requirements from its identification information and documentation. Check the route, floor, lifting equipment, and unloading plan with qualified riggers. A low purchase price does not reduce the cost or risk of moving a heavy machine.
What does the X/Y power-supply swap prove?
A fault that follows a component during a controlled swap narrows the search, because the changed component is now a stronger candidate than stationary parts. The inference is valid only when the swap isolates that component and the test conditions remain comparable. Record what was moved, retain the original configuration details, and avoid powering equipment with uncertain wiring or incompatible replacement parts.
Before accepting the supply as the root cause, request a test with a known-good compatible supply, if available. Then command small X movements in both directions and across a useful portion of travel, observing whether the original fault returns. If the fault remains with X, stop treating the power supply as the sole explanation and inspect the motor cable, axis drive, and mechanical movement. If it follows the supply again, obtain the correct replacement specification from the machine documentation or component label rather than guessing from “12 V.”
Intermittent faults deserve more than one brief jog. One reported Fadal X-axis problem was associated with a board and could be reproduced by vibration or temperature after a reset. That is a diagnostic possibility, not a confirmed explanation for this machine. Ask whether the fault returns after repeated operation and whether movement, cabinet temperature, or vibration changes its behavior. Do not use resets as a repair or as proof that the machine is sound.
How do you screen the ways and axis motion?
The most consequential mechanical concern raised for this machine is the condition of the Turcite on the ways. The reported inspection method is to jog the X axis to one side, remove a way cover, and look underneath the table. Inspect the exposed way surfaces and Turcite for visible separation or damage. If the inspection cannot be performed safely or the condition is unclear, arrange an experienced machinist’s inspection rather than inferring condition from the machine’s exterior.
With the machine powered and under the seller’s control, jog the table and Z axis through their travel and listen for abnormal or uneven sounds. Observe for binding, inconsistent motion, or an axis that faults. These checks are screening tests; they do not replace dimensional inspection or establish that the machine will hold accuracy under cutting load. Compare behavior across the travel and note where any noise or resistance occurs.
Keep the conditions and observations separate: a quiet jog does not prove good ways, and visible damage to a way does not by itself describe the full repair scope. If the X axis cannot be operated because of the reported fault, do not assume its mechanical condition from the Y or Z axis results.
What do spindle and tool-change tests add?
Run the spindle through its available operating range while listening for rough, uneven, or otherwise abnormal sound. A smooth sound during a short test is a useful screen, not proof of spindle health under load. Ask whether the seller can demonstrate tool changes and observe whether the machine completes them without interruption or abnormal noise.
Test each function separately and note the result. A working spindle or tool changer does not verify X-axis condition; likewise, an X-axis fault does not establish a spindle problem. Together, these observations show which subsystems operate and which still need diagnosis.
How should you judge the control and electronics?
The Fadal control was described as command-oriented, similar to an older computer, and as a distinctive panel that may not transfer directly to other machine-tool controls. A first-time CNC owner can learn it, but the learning task includes both machining practice and learning this control’s workflow. If broad experience across different machine tools matters, account for the panel’s distinctiveness.
One inspection clue reported for the electronics cabinet is that the three axis-driver cards and main control card may have suffixes ending in -1, -4, or -6, with higher suffixes up to -6 described as preferable. Treat this only as a screening clue: identify each card, record its full marking, and check compatibility against machine-specific documentation before judging a configuration or buying replacement boards. A suffix by itself does not prove that a board works.
Check whether manuals, parts, and technical assistance for the exact machine configuration are accessible to you. Parts availability can make an older machine easier to repair, but it does not make an unknown fault inexpensive or simple. Set aside a repair budget and account for delivery, electrical service, tooling, and setup. One owner reported spending about $15,000 including transport and power; that is an individual example, not a cost estimate for this purchase.
Which findings should decide whether you buy?
Base the decision on the work needed to make the machine safe to move, power, and operate—not on the headline price alone. A buyer who is comfortable troubleshooting electrical systems still needs machining knowledge, rigging support, and a plan for mechanical inspection. If those resources and learning time are available, a fault that follows a replaceable supply may be a manageable entry point. If the X-axis fault is unexplained, the ways are damaged, or the machine cannot be demonstrated, price the purchase as an unresolved repair project.
- Ask for the exact X-axis fault indication and a precise account of the supply swap.
- Inspect the machine exterior, table, accessible wiring, X-axis motor conduit, and cable.
- Inspect the ways by moving X to one side, removing the way cover, and viewing underneath the table.
- Observe X and Z jogging, spindle operation, and tool changes; record any fault, unusual sound, or inconsistent motion.
- Read and record the electronics card markings, then confirm the machine’s documentation, parts path, power requirements, and move plan.
- If the supply is replaced or exchanged with a compatible known-good unit, repeat the X-axis test under comparable conditions and confirm the original fault stays cleared.
FAQ: What should a first-time Fadal 4020 buyer check?
What happens if the X-axis fault follows the Y-axis power supply?
The supply becomes a leading suspect if the swap moved only that component and the fault moved with it. Repeat the test with a known-good compatible supply and verify that X moves repeatedly without the fault.
What happens if the X-axis fault stays with X after the swap?
Shift the investigation to the X-axis drive, motor cable and conduit, control path, and mechanical load. Get the exact fault indication and inspect the cable for damage before concluding that the supply is responsible.
What happens if I cannot inspect the Turcite on the ways?
You cannot use an exterior inspection or a jog test as a substitute for seeing the way condition. Arrange an inspection by an experienced machinist or treat the mechanical condition as unresolved in your purchase decision.
What happens if the spindle sounds smooth during a short run?
A smooth sound is a useful screening result, but it does not prove spindle health under cutting load. Record what was tested and consider a more complete inspection before relying on the spindle.
What happens if the replacement supply clears the X-axis fault?
Repeat X-axis moves in both directions and through useful travel, then confirm the fault does not return during repeated operation. The purchase verification ends only after the axis completes those tests without the original fault.