A gearbox that is correctly selected and badly installed will still fail early - and the warranty claim will look exactly like a design fault. surveys of returned units keep finding the same small physical causes: a foot bolted down over a gap, a coupling aligned to the eye instead of the gauge, a torque arm pinned to steel that moves when the machine runs. None of these show up at the test bench. All of them show up in the bearings.

This guide walks through the installation as the fitter meets it: what the foundation has to do, how soft foot hides in the bolts, what shaft alignment means in practice, and how hollow-shaft and torque-arm arrangements change the checklist. It closes with the records worth keeping from the first hour of running.

Why the Installation Decides More Than the Catalogue Does

Gearing inside a modern industrial unit is designed and manufactured to tolerances far tighter than anything on the surrounding steelwork. The bearings that carry the gear sets assume their housings stay round and their loads stay distributed. The installation is where those assumptions are either honoured or quietly broken.

The failure pattern is predictable. A distorted case bends the bearing bores, the internal clearances close on one side, and the bearing runs hot in a way that looks like lubrication trouble. A misaligned coupling adds a cyclic axial force the thrust bearing was never given in the duty calculation. Neither fault appears on a purchase order, and both are expensive to find later, which is why the installation phase deserves the same seriousness as the selection phase.

The Foundation: Mass, Level and Access

A foundation does three jobs. It carries the static weight and the running reactions without moving, it keeps the drive shafts in their designed relationship to the driven machine, and it gives the fitter somewhere honest to measure from. Concrete pads and fabricated steel bases both work; the difference is usually stiffness and curing time rather than principle.

Shims deserve a paragraph of their own. They are for setting level, not for absorbing a badly finished pad. A stack of thin shims under one foot acts as a spring, and a spring under a foundation bolt relaxes with temperature and time - which is precisely how a drive that ran quiet at commissioning develops a hum by the end of the year. Where the pad is poor, the answer is a machined sole plate or a resin grout repair, not more shims.

Soft Foot: The Small Error That Hides in the Bolts

Soft foot exists when tightening one foundation bolt changes the shape of the case. The gap under one foot closes as the bolt draws it down, the case distorts, and the bearing bores move with it. The drive may run acceptably at first, then develop elevated vibration once temperatures settle, and the cause will be found - if it is found - under a foot, not inside the gearbox.

The check is simple and belongs in the installation record. Loosen each foot bolt in turn and watch the foot with a dial indicator or a feeler gauge; any foot that lifts measurably when its bolt is released is a soft foot. Correct it at the seating - machining, grinding or a single properly fitted shim under the whole foot area - and recheck until releasing any bolt moves nothing. The whole exercise costs less than one bearing.

Shaft Alignment: What Good Actually Looks Like

Coupling alignment compares the position of the two shafts, not the position of the coupling parts. The distinction matters because couplings flex, cases have casting tolerances, and the eye is optimistic. Two measurements matter: offset between the shaft centrelines at the coupling, and angular misalignment - the difference in slope between them.

Rim-and-face dial indicator work is still the site standard. A rim reading gives the offset; face readings at two positions give the slope. Laser systems do the same geometry faster and less dependently on operator touch, and they earn their keep on trains where thermal growth moves the shafts between cold and hot. Either way, the target is the coupling manufacturer's tolerance for the speed involved, adjusted for the thermal growth the manufacturer of the machine expects between cold alignment and running temperature.

Two habits keep the numbers honest. First, align cold only after agreeing the thermal offset with the machine supplier, because a motor that grows on its feet will move a perfectly cold alignment out of tolerance by afternoon. Second, record the final figures and keep them with the drive. Alignment is not a one-time event; the recorded cold numbers are the baseline every future check is compared against.

Hollow Shaft and Torque-Arm Installations

Hollow-shaft mounting removes the coupling from the drive train and replaces it with the bore-to-shaft fit, which moves the alignment conversation onto the driven shaft itself. The gearbox hangs on the shaft, so the shaft's own runout, its bearing condition and the fit at the seat decide how the drive runs. A worn outboard bearing on the driven shaft will be felt by the gearbox bearings, whatever the coupling table says.

The bore fit deserves the same care a coupling gets: clean and deburred the seat, confirm diameter and keyway against the drawing before lifting the unit, and never correct a loose fit with welding or packing - the correct answer is a bushed or keyed rebuild at the shaft. For torque-arm builds, the arm and its stay complete the geometry. The stay wants to be long enough that angular changes do not multiply pin loads, pinned through bushed holes with a grease point the shift routine can reach, and the structure receiving the reaction should be checked for a stall, not just for running torque. The MC2RLHT03 right-angle hollow shaft gear unit is a typical frame for this arrangement, and the same installation logic applies across the family.

The First Run: Baseline Records Worth Keeping

The first hours of running are the cheapest opportunity the drive will ever give you to record what healthy looks like. A short baseline set costs an hour and pays for itself the first time something sounds different:

• Vibration readings at each bearing housing, both directions, with the dates and speeds noted.
• Case temperature at a marked point after a fixed running period, so future readings compare like with like.
• Oil level and condition as installed, plus the breather type fitted.
• Alignment figures - final cold numbers and any thermal offset agreed with the machine supplier.
• Soft foot check result - the confirmation that releasing each bolt moved nothing.

Six months later, when a sound changes or a reading drifts, that baseline is the difference between a trend and a guess. Maintenance teams inherit drives without history more often than not; the installation record is the cheapest history a drive can own.

Common Questions

How level does a gearbox foundation actually need to be?

Level enough that the machined foot pads contact their seating everywhere without shims pulling the case into shape, and flat enough that the shaft relationship to the driven machine holds through the thermal cycle. The precise figures come from the drive drawings and the coupling tolerance, but the practical test is the soft foot check: if releasing any bolt lifts the foot, the base is not ready for the bolts.

Can alignment be checked without coupling halves fitted?

Roughly, but not conclusively. Measuring between the shaft ends with the halves removed can show gross errors, yet the accepted practice is to align with the coupling fitted and the readings taken on machined surfaces, because coupling runout and fitting tolerances become part of the measurement once installed. Final verification belongs on the assembled train.

How often should alignment be rechecked?

At every major overhaul, after any event that moves the machine - a belt replacement that changed tensions, structural work nearby, a foundation repair - and whenever vibration or temperature trends move without a process explanation. Drives with a recorded baseline only need comparison against it, which is the strongest argument for recording the numbers at commissioning.

Does a torque arm need torqueing to a figure?

The pins and bolts want the fastener's own torque specification, and the arm geometry wants checking rather than force: stay length, bushed pin fit and a bracket that does not flex under a stall. Overtightening a stay to compensate for poor structure simply moves the distortion into the frame; the reaction path should be stiff by design, not by bolt tension.

The Order That Makes Installation Easy

Installation quality starts before the drive ships. The enquiry that names the shaft details, the mounting arrangement, the breather position and the service side lets the supplier confirm clearances and the arm geometry while changes are still cheap - the same duty points that size the frame through the online selection system also settle the installation questions, and a correctly specified hollow shaft frame arrives ready to sit flat, turn true and record a clean baseline.

Get the foundation honest, the bolts gap-free, the alignment recorded and the baseline taken - and the gearbox spends its life doing the only job it was ever asked to do: turning torque quietly, for years, without a story to tell.