Orbital or belt sander won't work or vibrates — Riga repair guide

You switch the sander on and the pad won't spin, it just hums in place, it hammers your hands with too much vibration, or the belt walks off the rollers — when a random-orbital or belt sander won't work or vibrates, it almost always points to one worn part, not a dead tool. This is an honest read from the bench: how to tell harmless wear from a serious fault, what you can safely check yourself, and where the service work begins. We cover both common sander types — random-orbital and belt — because they fail on different principles.

First unplug it and work out which one you have

Before anything else, pull the plug from the socket or remove the battery. The pad and the belt move at high speed, and an accidental start during a check is a real risk to your fingers.

The two types look different, and they fail differently too:

• A random-orbital sander spins a round or square pad through a small orbit. Under the pad sit a bearing and an eccentric (counterweight) that turn the motor's rotation into that orbital motion. The classic fault here is vibration and a loud hum.
• A belt sander drives an endless sanding belt over two rollers. The classic fault here is the belt drifting sideways or running unevenly.

Many symptoms — internal sparking, a motor that hums but spins nothing, a bad switch — are shared by both types and by every corded power tool. We cover those separately below.

Random-orbital sander: bearing, eccentric and pad

The heart of a random-orbital sander is the assembly under the pad: a shaft with a counterweight (the eccentric) running on a bearing. That bearing is the part that wears out most often.

Typical symptoms and their causes:

A worn bearing is the single most common random-orbital fault. At first it only hums louder and vibrates more; keep running it and the bearing collapses completely, the eccentric starts to rub against the housing, and the assembly can seize. A bearing swap is a typical, predictable repair.

The other frequent culprit is a worn pad — both the platform itself, with the hook-and-loop surface the sandpaper grips, and the cushioning backing pad behind it. If the paper no longer holds or the pad has gone hard and rough, sanding turns uneven while the motor and bearing are still sound.

What you can check yourself

1. With the machine unplugged, turn the pad by hand. It should move smoothly, with no rattle and no catching.
2. Rock the pad up and sideways. A lot of play or rattle points to a worn bearing or eccentric.
3. Inspect the hook-and-loop surface: if the hooks are worn flat and the paper won't stick, the fault is the platform alone.
4. Clear the dust channels (see the section below) — very often a blockage mimics a heavier problem.

On many models the hook-and-loop platform is a part you can replace yourself — it is a simple, commonly stocked component. But changing the bearing or eccentric means opening the housing, a press, and the correct spare part; leave that to the service centre.

Why the pad vibrates or 'coughs' irregularly

It is worth singling out the case where the sander won't run smoothly or vibrates intermittently — it works fine, then jolts now and then, 'coughs', or briefly loses revs. This is rarely the bearing (bearing vibration is steady and constant) and more often points to the electrical side.

The most common causes, from simplest to more serious:

1. Worn carbon brushes. These are the sliding contact between the stationary windings and the spinning commutator. When the brushes wear down to the nub, the contact turns unstable — the machine jolts, loses power, sparks under the ventilation slots, and finally cuts out. Brushes are a simple, commonly replaced part.
2. A worn or dirty commutator. Sparking brushes burn the commutator segments over time. If the commutator is black or grooved, new brushes alone won't help.
3. A failed speed control or switch. Many sanders have speed-control electronics; when it fails it causes jolting and unexpected speed changes. A bad switch contact gives a similar effect.
4. A partially seized bearing. Rare, but a collapsing bearing can shift the load and produce a 'cough' under the motor.

Self-check: on many models the brushes sit behind screwed caps on the sides of the housing — you can remove and inspect them. If a brush is worn down to a few millimetres or cracked, it is replaceable. Even so, the service centre still needs to check the commutator, which sparking brushes tend to scar.

Belt sander: belt drifts or won't run — tracking and roller wear

The signature belt-sander fault is a belt that drifts sideways and off the rollers or off the platen. It is rarely the motor's fault — the cause is almost always in the rollers and their adjustment.

Many belt sanders drive the belt through a drive belt between the motor and the drive roller. If that drive belt snaps or slips off, the motor hums but the sanding belt stands still. It is a typical, easily replaced fault.

Tracking is the simplest cause: most belt sanders have a small adjustment knob or screw for the front roller. If the belt drifts sideways with a brand-new belt fitted, adjust the tracking first — often that is all it needs.

But if the belt still drifts after adjustment, the roller itself is worn: either the front (idler) roller with its bearing, or the drive roller's rubber coating, which hardens and goes smooth over time. In that case the belt won't stay on no matter how you adjust it, and the roller has to be replaced.

What you can check yourself

1. Fit a new, undamaged belt — an old, stretched or kinked belt drifts on its own.
2. Adjust the tracking knob in small steps, running the machine briefly and unplugging it again between steps.
3. With the machine unplugged, turn the rollers by hand — they should spin freely, with no rattle and no catching.
4. Inspect the rubber coating: a shiny, smooth, hardened roller no longer holds the belt.

A clogged dust extraction as a hidden cause

Dust extraction is a frequent, overlooked cause of vibration and overheating on both sander types. Fine sanding dust collects in the extraction channels, the filter, the bag, and around the cooling fan.

What it causes:

• Blocked cooling airflow → overheating. The motor and electronics cool by airflow through the housing. When the ventilation slots clog, the motor overheats, smells of hot insulation, and finally shuts off or burns out a winding.
• Dust in the bearings → rough running. Fine dust works into the eccentric bearing and the roller bearings, accelerating wear and producing vibration.
• A full bag/filter → back pressure. A full dust bag weakens extraction, so dust stays under the pad and builds up on the sanding surface.

The self-check is simple and safe: with the machine unplugged, clear the extraction channel, empty the bag or filter, and clean the ventilation slots with a brush and compressed air (wear eye protection). Quite often a blockage is exactly what mimics a heavier problem — after cleaning, the vibration and heat ease off. If the smell and overheating remain after cleaning, the problem is in the motor and worth showing to the service centre.

Shared electrical faults: brushes, switch, cord

These symptoms are common to every corded power tool — both random-orbital and belt sanders:

• The machine won't switch on at all. Check the socket, the extension lead and the cord first (on cordless models — the charge and the contacts). The fault is often a broken cord right at the housing or at the plug, where it flexes most.
• Switches on but cuts out at once / sparks inside. The most typical cause is worn brushes or a burnt commutator.
• The switch must be held in or it 'jumps'. A worn switch with a poor contact — a separate replaceable part.
• A burnt-insulation smell. Unplug immediately and stop using it. This points to an overheated or burnt-out winding and needs the service centre.

You can check the cord, the plug and externally accessible brushes yourself. Diagnosing the winding, commutator and internal electronics takes disassembly and instruments — do that at the service centre. A similar split between self-help and service is described in the article on when an angle grinder won't spin or sparks.

When a sander is cheaper to replace than to repair

Sanders are mostly repairable, and replacing one worn assembly is usually more worthwhile than buying a new tool. But not always — a lot depends on whether the fault is local and whether the parts are still made.

The simple principle: if one local part is damaged — a bearing, roller, belt, brushes, platform or switch — and the housing and motor are sound, replacing that one worn assembly is cheaper than a whole new tool. If several things fail at once, or the motor winding has burnt out on a basic machine whose parts are no longer made, the balance tips toward replacement — and we say so plainly at inspection.