Machine vibrating, noisy or running hot
A new noise is information. Grinding or screeching means stop now. A growl that rises and falls is chatter. Buzzing at rest is usually motor current. A router too hot to touch is a duty cycle or a cooling problem.
A sound or a temperature that is different from normal. New noises are diagnostic information, and the ones that mean stop immediately are worth knowing by ear.
first
Diagnostic steps: sounds, and what they mean
| Sound | Usual meaning | Action |
|---|---|---|
| Grinding or screeching from the cut | Dull bit, or the tool buried and not clearing | Stop now. Inspect the bit and the cut. |
| A growl that rises and falls | Chatter | Reduce engagement and stickout |
| Rhythmic clunk during a cut | Steps being lost, or something hitting | Stop and find it. See lost steps. |
| Buzzing or humming when stationary | Normal stepper holding current, usually | Nothing, unless motors are getting hot |
| Whining that changes with axis speed | Normal stepper resonance at some speeds | Usually nothing, but check for binding |
| Rattling from the machine, not the cut | Something loose | Full fastener check |
| A squeal from the router | Bearings, or brushes near the end of their life | Investigate before a long job |
| Sudden change in pitch mid-cut | The cut changed: a knot, a void, or the bit slipping | Watch closely, check the bit mark |
Heat
- Router body hot. Trim routers have a duty cycle and they draw cooling air through themselves, which means they also draw dust. Give them breaks on long jobs, keep the vents clear, and consider whether a spindle suits your work better.
- Stepper motors hot. Normal, and more normal than people expect: steppers are rated to run at temperatures well above what a hand will tolerate, so too hot to touch is not by itself a fault. A motor that is dramatically hotter than its neighbours, or hot with the machine idle, is worth checking the driver current on.
- Bit hot. See burning. It is a chipload symptom.
- VFD or drivers hot. Check ventilation and that the enclosure is not packed with dust.
Most likely causes of a new vibration
- Fasteners loosened over timeMost common
Vibration loosens things, and loose things vibrate more. Periodic checks prevent this. - V-wheels worn or out of adjustmentCommon
Adjust eccentric nuts so there is no play but the wheel still turns freely. - Belt tension lostCommon
Belts stretch. Check tension and look for worn teeth. - Router bearings wearingOccasional
A growl with the router running and no cut is a clear sign. - Bent or damaged bitOccasional
Spin it by hand and watch the tip for a wobble. - The bench the machine sits onOccasional
A flexy table transmits and amplifies everything. Especially relevant on machines where you supply the table.
Fixes
- Stop for grinding or screeching, then inspect the bit and the cut before anything else.
- Do a full fastener check with the machine off: router mount, Z assembly, gantry, motor mounts, couplers.
- Adjust V-wheels and belt tension to the maker's procedure. No play, free rotation.
- Swap the bit for a known-good one to rule out a bent or damaged cutter.
- Give a trim router a rest on long jobs, clear its vents, and replace brushes when the squeal starts.
- Stiffen the bench or move the machine to a heavier one.
Why it happens
A CNC is a stack of parts held together by fasteners, and it spends its life shaking. Every fastener loosens a little with every hour of vibration, every wheel and belt wears, and the router's bearings and brushes have a finite life. None of it fails all at once. A new sound is the machine reporting that one of those slow processes has crossed a threshold, which is why the sound arrives before the symptom shows in the work, and why it is worth acting on the sound.
Prevention
- Put a fastener and wheel check on a schedule: monthly, or every 20 hours of cutting, whichever comes first.
- Keep the router's vents clear and keep spare brushes on the shelf.
- Learn the normal sound of a good job so a change registers immediately.