Five signs your router spindle is about to fail

Most of the spindles that reach our bench were telling their operators something for weeks first. A bearing does not fail in an afternoon; it wears, warms, loosens and then, one day, seizes or scores the shaft. Catch it at the first sign and it is a bearing job. Catch it at the last and it is a shaft, a housing and a longer wait.

1. It is getting louder, and the noise climbs with speed

A healthy high-frequency spindle makes a smooth, even whine that rises cleanly with rpm. A bearing on its way out adds a rumble, a growl or a higher, harsher note that gets worse as the speed goes up. Operators often notice it during the ramp to full speed rather than during the cut.

What it means: the rolling elements or races are pitted, the cage is damaged, or the grease has broken down. It will not get better.

2. The housing runs hot

Some warmth is normal, especially on fan-cooled units after a long run. A spindle you cannot keep a hand on, or one that is markedly hotter than it used to be at the same job, is losing bearing preload or lubrication, or its cooling has stopped doing its work. On air- and liquid-cooled spindles, check the supply first: a dry air line or a tired chiller will cook a good bearing set.

3. Vibration you can feel through the machine

Vibration is either imbalance or bearing play. Rule out the easy things: fit a fresh, balanced tool in a clean collet and run it at the usual speed. If the vibration goes, it was the tooling. If it stays, it is the rotor or the bearings, and it is doing damage every minute it runs.

4. The finish has gone off

Chatter marks, witness lines at the tool path, a surface that needs more sanding than it did last month. Bearing play shows up in the cut long before it shows up in the noise, because the tool tip is being let wander by a few microns on every revolution.

5. Runout at the collet has grown

Put a dial indicator on a ground pin held in the collet and rotate the spindle by hand. A rebuilt spindle reads a few microns; a worn one reads a lot more. If the number has grown since the machine was new and a fresh collet does not fix it, the bearings or the shaft are the reason.

Two more that people miss

Tool changes that fail or tools that pull out on an automatic tool-change spindle point at the drawbar, the gripper fingers or a scored taper. That is a rebuild job too, and a cheaper one than a spindle that has thrown a tool.

Drives that trip on overcurrent, or a motor that has lost torque, can be windings, an encoder, a cable or the drive itself. We isolate the motor from the bearings before quoting, so nobody rebuilds a spindle that needed a cable.

What to do

Stop running it. Note the symptom and the speed it appears at, take a photo of the nameplate, and send us the details. Standard turnaround is 3 to 5 working days from receipt; there is an emergency service when the queue cannot wait.