It removes the alignment problem entirely, along with the foundation.

A conventionally mounted reducer sits on its own base and connects to the driven shaft through a coupling. That coupling must be aligned within tight tolerances, and staying aligned depends on the base and the driven machine not moving relative to one another. On a conveyor - a long flexible structure that carries variable load, sits outdoors and settles - they move constantly.

A shaft-mounted unit is carried on the driven shaft itself. There is no relative movement to accommodate because the gearbox and the shaft are effectively one assembly. Misalignment cannot develop.

It also removes the cost of fabricating and grouting a base, reduces installation time considerably, and makes the drive a package that can be fitted by fitters rather than requiring a millwright with alignment equipment.

Anchored to something rigid, angled so it works in tension, and fitted with a resilient bush - and getting this wrong is the usual source of trouble with these drives.

The arm carries the full reaction torque, so its anchor point must be genuinely rigid. Bolting it to thin sheet or to a bracket that flexes transfers vibration into the structure and cracks the bracket.

Orientation matters: the arm should ideally be positioned so the reaction puts it in tension rather than compression, since a rod in tension cannot buckle.

The resilient bush at the anchor end absorbs the shock of starting and of load changes. Anchoring the arm rigidly with no bush transmits every impulse straight into the frame.

Arm length also matters. A short arm carries a higher force for the same torque, so the manufacturer's recommended length should be followed rather than shortened to suit a convenient anchor point.

By a keyed bore, a taper bushing or a shrink disc, and the choice affects removal as much as it affects torque capacity.

A keyed hollow bore is simplest and cheapest. It transmits torque through the key, but under reversing or shock loads a keyed fit can fret and can become extremely difficult to remove after years in service.

Taper bushings grip by wedging as the bolts are tightened, giving a tight concentric fit, and can be released by using the bolts in the extraction holes - which makes removal predictable.

Shrink discs clamp the hollow shaft onto the driven shaft by friction around the full circumference. They carry high torque, are free of backlash and fretting, and release cleanly.

On a conveyor drive that will be removed for maintenance, the removal method is worth as much thought as the torque rating. A drive that cannot be got off the shaft turns a bearing change into a shaft replacement.

Because it adds ratio flexibility and provides shock absorption ahead of the gear train.

The gearbox provides a fixed ratio, but conveyor speed frequently needs adjusting during commissioning or when the process changes. Changing a belt pulley is a cheap and quick way to trim the overall ratio without replacing the gearbox.

Belts also slip under severe overload, which protects the gear train from the shock of a jammed conveyor or an abrupt start - a mechanical fuse that a direct coupling does not provide.

The arrangement mounts the motor on the same bracketry as the reducer, so the whole drive is one assembly that bolts to the frame, and belt tension is set by adjusting the motor position.

The costs are the guarding required, periodic belt inspection and tensioning, and a small efficiency loss. On conveyor duty these are generally accepted readily.

On any inclined conveyor where the loaded belt would run backwards if the drive stopped - and it should be treated as a safety item.

An inclined conveyor carrying material has potential energy in the load. Remove the driving torque and gravity drives the belt backwards, accelerating as it goes. That discharges material at the tail end, can injure anyone nearby, and can wreck the conveyor.

A backstop is a one-way clutch that allows rotation in the driving direction and locks in the other. It is commonly built into the reducer or fitted to a shaft extension.

The critical detail is direction. A backstop fitted the wrong way round prevents the conveyor running at all, which is obvious - but a backstop that has been removed during maintenance and not refitted is not obvious at all until the power fails.

Size it for the actual runback torque from the loaded incline, not for the drive torque.

Conveyor duty is demanding, and the service factor should reflect starting under load rather than steady running.

A loaded conveyor is one of the harder things a gearbox can be asked to start. Breakaway torque with a full belt substantially exceeds running torque, and if the conveyor is started loaded regularly the gearbox sees that peak every time.

The number of starts per hour matters as much as hours run. Frequent starting under load is more damaging than continuous running at the same torque.

A belt input helps by slipping under the worst peaks, and a soft starter or inverter on the motor helps more by limiting the torque applied at all.

Apply the manufacturer's service factor for conveyor duty with the actual start frequency, and state whether the conveyor can be started loaded. A gearbox chosen for a conveyor that is always started empty will not survive one that is regularly started full.

Usually yes, and retrofitting one to replace a failed foot-mounted drive is common - provided the shaft and the anchor point are suitable.

Check three things. The driven shaft must have a sufficient plain length of the right diameter for the hollow bore, and must be in good condition where the bore will grip - a worn or stepped shaft end is a problem. There must be a rigid anchor point at roughly the right distance for the torque arm. And there must be clearance for the gearbox body and the belt drive alongside the conveyor.

Measure the existing shaft rather than working from drawings, since shafts get replaced and repaired over a conveyor's life.

The retrofit usually simplifies the installation considerably - the old bedplate and coupling can often be removed entirely - and it removes the alignment maintenance that the original drive needed.