How to Remove a Servo II Motor from a CNC Machine
This guide is for maintenance techs and engineers who need to pull a Servo II series motor without losing axis alignment or damaging the encoder. It covers lockout, marking, coupling separation, cable handling, and the checks that decide whether the axis will hold tolerance after reassembly.
In this article
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
What matters before you touch a bolt
Prepare the machine before you remove a servo ii motor
Pulling a servo motor is a mechanical job wrapped in an electrical one. The motor holds the axis position through the drive, and the drive holds its own reference through the encoder. Break either link without a record and the machine will not know where the axis is when you power back up.
Start with the electrical side. Isolate the drive at the cabinet breaker, apply lockout, and wait for the DC bus to discharge. Most Servo II class drives bleed down within a few minutes, but confirm with a meter on the bus terminals rather than trusting the indicator LED. Some cabinets keep a residual charge that will bite through a ring.
Wear safety glasses, nitrile gloves, and a grounded wrist strap when you handle connectors. The encoder signal runs at low voltage and is easy to damage with static. Keep the strap connected until the last connector is in its bag.
Set up a clean bench within reach. You need a torque wrench in the 5–50 N·m range, a dial indicator with a magnetic base, a puller sized for the hub, a digital caliper, and labeled bags for fasteners. Photograph the motor, cable routing, and connector orientation from at least three angles before anything moves.
- 1Record the axis zeroWrite down the machine coordinate and any grid shift value for that axis.
- 2Photograph cable routingInclude any clamp, conduit, and drip loop positions.
- 3Label every connectorPower, encoder, brake, and thermostat leads can look alike at a glance.
- 4Check for a brakeA vertical or inclined axis may need the brake released or mechanically blocked.
Flange, foot, and direct-coupled mounts behave differently
On most CNC axes, the Servo II motor bolts to a bracket or gearbox flange with four socket-head screws. The shaft connects to the ball screw through a coupling, a timing belt, or a gearbox input. Which one you have decides the removal sequence and how much alignment work follows.
Direct-coupled motors are the least forgiving. The coupling sits between two shafts with almost no radial room, so the motor must come out on the same centerline it went in. If the bracket has dowel pins, leave them in the bracket and lift the motor straight off. If you fight a doweled joint, you are pulling against steel, not paint.
Belt-driven motors tolerate more misalignment, but the pulley position sets belt tension. Mark the pulley on the shaft before you loosen the taperlock or the clamp hub. A pulley that slides 2 mm inboard will change the belt plane and can throw the axis tuning off even when the zero is restored.
Foot-mounted motors on a machined pad are the easiest to remove but the easiest to misalign on refit. Clean the pad and check for burrs. A single chip under the foot can tilt the motor by several tenths of a millimeter over a 100 mm base, which shows up as a periodic error in the axis motion.
Mark the joint so refitting is repeatable
The goal of marking is not to identify parts. It is to put the motor back in the same angular and axial position so the coupling does not fight the axis zero. Two reference marks are enough: one on the motor flange against the bracket, and one on the shaft against the hub.
Use a sharp scribe or a light center punch on a machined surface. Paint or marker lines are fine as a secondary reference, but they disappear under coolant and cleaning solvent. Punch marks on a hardened shaft should be shallow, roughly 0.1 mm deep, so they do not create a stress riser.
If the coupling has a key, note which side of the keyway faces up. If it uses a clamp hub with a single pinch bolt, mark the gap position. On taperlock bushings, mark both the bushing and the pulley because the assembly moves as one unit.
Measure the axial gap between the motor flange and the bracket at two opposite points. Write both numbers down. This gap tells you how much shim you need on refit, and it is the fastest way to catch a bracket that has shifted during removal.
What to inspect while the motor is out
The window between removal and refit is the only easy chance to check parts that are hidden when the motor is bolted up. Spend twenty minutes here and you can avoid a second teardown.
Look at the coupling element first. Bellows couplings should show no cracked convolutions and no polishing from slipping. Jaw-type spiders should not be compressed or torn. A clamp hub with a visible gap at the slit is fine; a hub with no gap left is at the end of its clamp range and should be replaced.
Check the motor shaft for fretting, a ring of reddish-brown wear where the hub sat. Light fretting cleans up with a fine stone. Deep fretting means the hub was running loose and the shaft diameter may be undersize.
Inspect the bracket for cracks around the mounting holes and the encoder cable for a sharp bend radius. The cable should not be bent tighter than about 10 times its outer diameter. A kinked encoder cable can pass a static check and still drop counts during rapid moves.
Removal errors that cost a full day of realignment
The most expensive mistake is pulling the motor with the coupling still clamped. The hub acts as a wedge, and the load goes straight into the motor bearing and the ball screw thrust bearing. If the motor will not slide after a light pull, something is still clamped.
The second is lifting at an angle. A Servo II shaft and a ball screw end are both precision surfaces. Side loading them with the weight of the motor can brinell a bearing race, which shows up later as a rough spot in the axis travel.
The third is losing the flange gap measurement. Without it, you do not know whether a shim fell out or the bracket moved. Techs then chase the zero with the coupling, which loads the shaft and shortens bearing life.
Finally, do not pull on the encoder cable to move the motor. The cable is not a handle. A stretched encoder lead can test fine at rest and lose counts under acceleration, which sends you looking for a drive fault that is not there.
- 1Do not hammer the shaftUse a puller on the hub, never impact on the motor shaft end.
- 2Do not reuse a stretched keyA key that rocks in the keyway will develop play within weeks.
- 3Do not leave the encoder plug openOne chip in the pins is enough to cause an intermittent fault.
Step by step: remove a servo ii motor
Work in this order. Skipping the recording step is the most common cause of a long realignment job.
- 1Record the position and reference valuesNote the machine coordinate, any grid shift, and the drive parameters you can read without powering the axis. Photograph the screen. This is your only reliable baseline.
- 2Lock out and verify zero energyOpen the cabinet breaker, apply your lock, and meter the DC bus. Wait until it reads below 5 V before touching terminals. Release the brake only if the axis is mechanically supported.
- 3Disconnect power, encoder, and brake leadsLabel each connector. Pull on the housing, never the wires. Cap or bag the encoder plug immediately to keep chips and coolant out.
- 4Mark the flange and shaft jointsScribe one line across the motor flange to the bracket, and one across the shaft to the hub. Measure the flange gap at two points and record both values.
- 5Loosen the coupling or pulleyFor a clamp hub, loosen the pinch bolt and check for a second set screw under it. For a taperlock, remove both screws and use one as a jack screw to release the bushing. Do not pry between the hub and the motor face.
- 6Support the motor and remove the mounting screwsSling or block the motor before the last screw comes out. Loosen the four socket screws in a diagonal pattern, a quarter turn at a time, to avoid cocking the flange.
- 7Slide the motor straight off the shaftPull on the centerline, not at an angle. If it will not move after 2–3 mm, stop and check for a hidden dowel, a second set screw, or a burr on the shaft.
- 8Bag, label, and store the hardwareKeep the screws with the motor. Place the motor on a clean pad, not the floor. Cover the shaft and the encoder connector before you walk away.
Match the removal method to the coupling type
Use this to pick the right puller, marking method, and refit check.
| Coupling type | Removal approach | Refit check |
|---|---|---|
| Bellows clamp hub | Loosen pinch bolt, check for second screw, slide off | Backlash under 0.02 mm at the hub |
| Jaw spider | Remove both hubs; keep spider with motor side | Spider not compressed; 0.5–1 mm gap set |
| Taperlock bushing | Use jack screw to release; never pry the pulley | Bushing flush with pulley face after torque |
| Timing belt pulley | Mark shaft, loosen taperlock or clamp, slide pulley | Belt plane within 0.5 mm of original mark |
| Gearbox input | Separate at the coupling, leave gearbox in place | Runout at motor flange under 0.03 mm |
| Doweled bracket | Lift straight off the dowels; do not twist | Dowels slide in by hand, no hammer needed |
The short version
Record the zero, mark the joint, support the weight, and pull on the centerline. Do those four things and the refit is a measurement job, not a guessing game.
Questions engineers ask before pulling a servo motor
Do I have to re-zero the axis after removing a Servo II motor?
Yes, unless the encoder is absolute and the battery was never disturbed. On an incremental encoder, the drive loses its reference when the motor is unplugged or the coupling is broken.
Even with an absolute encoder, the mechanical zero can shift if the coupling was clamped at a different angle on refit. Always verify with a dial indicator against a known surface before running a program.
Can I remove the motor without taking the pulley off?
Only if the pulley clears the bracket and the belt can be slipped off first. Mark the pulley position on the shaft before you loosen anything.
If the pulley has to move, treat it as a separate alignment step. A pulley that shifts 1–2 mm along the shaft changes the belt plane and can cause edge wear on the belt within a few hundred hours.
How much force should it take to slide the motor off the shaft?
A clean, correctly sized fit should move by hand or with light pry pressure on the flange, not on the shaft. If you need a puller to separate the motor from the coupling, the fit is too tight or something is still clamped.
Stop and check before adding force. Galling on the shaft or a burred keyway can turn a ten-minute job into a shaft replacement.
What should I check on the encoder cable routing?
Look for sharp bends, abrasion against a cabinet edge, and any place where the cable is used as a strain relief. The bend radius should stay above roughly 10 times the cable outer diameter.
Check the connector shell for cracks and the pins for corrosion. A green tint on a pin means moisture has been in the plug, and that connector will fail again unless it is replaced.
Is it worth replacing the coupling while the motor is out?
If the backlash at the hub is above 0.02 mm, the element shows cracks or polishing, or the clamp hub has no gap left, replace it. The cost is small compared with a second teardown.
If the coupling is clean and within backlash spec, keep it and reuse the same marking. A new coupling adds a break-in period that can shift the axis zero slightly in the first hours.
When should this job go to an outside shop?
Send it out when the motor shaft is fretted or undersize, when the bracket is cracked, or when the machine needs a full geometric realignment after the swap. Those jobs need a surface plate, a laser interferometer, and a controlled environment.
For a straight remove-and-refit with a good coupling and a clean shaft, an in-house tech with the right puller and a dial indicator can handle it.
Need a replacement bracket or coupling hub machined?
Send us the drawing or the worn part. We quote and return a DFM analysis within 12 hours, and parts ship in 3–5 days with 100% inspection.
12-hour quoteNo minimum order±0.005 mm tolerance
More CNC maintenance and machining notes
We publish setup notes, tooling trials and inspection data from the factory floor.
