Speed Increaser Alignment Procedures: A Guide to Laser Alignment Techniques

Speed increaser alignment is the process of positioning a speed increaser’s input and output shafts so their rotational centerlines line up with the connected motor, pump, compressor, or generator. Getting this right matters more on a speed increaser than on a standard gearbox. The output shaft spins at a multiplied RPM, and that higher speed amplifies every alignment error.

Laser alignment has become the preferred method for speed increasers running at high output speeds. It delivers measurement precision at or below 0.001″ (0.025 mm), which is the kind of accuracy these units demand.

This guide covers why speed increaser alignment calls for tighter tolerances, the step-by-step laser alignment procedure, tolerance values by RPM, and how to address common issues that come up during the process.

Why Speed Increaser Alignment Demands Greater Precision

Speed increaser alignment needs tighter precision than standard gearbox alignment. Three factors drive this requirement: RPM multiplication, uneven thermal growth, and accelerated component wear at the output shaft.

RPM Multiplication Sets the Tolerance Target

A speed increaser takes a lower input RPM and multiplies it at the output. For example, a 3:1 ratio unit receiving 1,750 RPM input produces 5,250 RPM at the output shaft.

Alignment tolerances are always set by the fastest shaft in the system. For a speed increaser, that means the output RPM, not the input, determines how tight the alignment needs to be. An offset or angular error that might be tolerable at 1,750 RPM becomes destructive at 5,250 RPM, putting greater radial forces on output bearings with every revolution.

Thermal Growth Creates Uneven Expansion

The high-speed output side of a speed increaser runs hotter than the low-speed input side. This uneven heat distribution causes the output end of the gearbox housing to expand more than the input end.

An alignment performed at room temperature will shift once the unit reaches operating conditions. The output shaft centerline may rise vertically by several thousandths of an inch compared to the input. A proper laser alignment accounts for this by targeting an intentional cold offset that becomes correct at running temperature.

Misalignment Effects Compound at High Speed

These effects compound once misalignment is present. Offset misalignment forces the high-speed shaft to orbit around the true centerline, cycling radial loads on output bearings at the multiplied RPM.

Angular misalignment creates a bending moment at the coupling that reverses direction twice per shaft rotation. At the output speed of a speed increaser, this produces high-frequency vibration that stresses seals, couplings, and housing components.

Combined misalignment, where both offset and angular errors exist at once, is the most common condition in real installations and the most demanding to correct.

With those risks in mind, the next step is knowing how to perform a proper laser alignment on a speed increaser.

Laser Alignment Procedure for Speed Increasers: Step by Step

Laser alignment is the most accurate and repeatable method for aligning speed increasers. The procedure below walks through each stage, from preparation to final documentation.

Step 1: Pre-Alignment Inspection

Before setting up the laser system, check the installation for conditions that will interfere with a good alignment:

• Inspect the foundation and baseplate for cracks, corrosion, or looseness. A twisted or bowed baseplate makes precision alignment impossible.
• Check coupling condition. Worn gear teeth, cracked disc elements, or degraded flexible inserts will absorb misalignment during measurement and mask the true shaft positions.
• Disconnect or loosen piping, hydraulic lines, and electrical conduit attached to the gearbox. External strain from these connections can pull the housing out of position.

A few minutes spent on pre-alignment inspection prevents hours of chasing false readings later.

Step 2: Soft Foot Check and Correction

Soft foot occurs when one or more machine feet do not sit flat on the baseplate. It distorts the gearbox housing, shifts internal gear mesh patterns, and changes bearing preloads. On a speed increaser, this distortion at the high-speed output bearing is especially harmful.

To check for soft foot, snug all four hold-down bolts first, then loosen one bolt at a time. Measure vertical movement at that foot using a dial indicator or the laser system’s built-in soft foot function. Any foot showing more than 0.002″ (0.05 mm) of lift needs shimming before you move forward.

Use solid stainless steel shims. Avoid stacking more than three to four shims per foot. Thick shim packs compress under load and act like springs, letting the alignment drift over time.

Step 3: Rough Alignment

Use a straightedge across the coupling hubs to bring the shafts within roughly 0.020″ (0.5 mm) of alignment in both the vertical and horizontal planes. This step saves time during laser measurement by placing the shafts within the system’s initial capture range. It cuts down on the number of correction cycles needed during the precision alignment phase.

Step 4: Laser System Setup and Measurement

Mount the laser transmitter and detector on opposite sides of the coupling. Secure them to the shafts or solid coupling hubs with magnetic or chain brackets.

Enter the machine dimensions into the alignment system: the distance between front and rear mounting feet, the distance from each foot to the coupling center, and the coupling diameter.

Next, enter the alignment tolerances based on the output shaft RPM, not the input speed. This is where speed increaser alignment differs most from a standard gearbox setup. A common mistake is entering the input RPM, which produces tolerances that are too loose for the actual operating speed at the output.

Rotate the shafts together through at least three measurement positions, covering a 180° sweep at minimum. The laser system uses these readings to calculate offset and angular misalignment in both the vertical and horizontal planes.

Step 5: Making Vertical and Horizontal Corrections

Correct vertical misalignment first by adding or removing stainless steel shims under the gearbox feet. The laser system displays the exact shim thickness each foot needs.

Correct horizontal misalignment next by repositioning the movable machine laterally using jackscrews or adjustment bolts. Re-measure after each correction. Two to three correction cycles are typical before the readings fall within tolerance. Vertical corrections can shift horizontal readings, so check both planes after every adjustment.

Step 6: Thermal Growth Compensation

If the speed increaser manufacturer provides thermal growth data, enter those values as target offsets in the laser system before the final measurement. The system will aim for a cold alignment position that becomes correct at operating temperature.

When manufacturer data is not available, a practical guideline is 0.001″ (0.025 mm) of vertical rise per 10°F of temperature increase per foot of shaft centerline height above the base. This estimate gives you a starting point until actual thermal data is collected during commissioning.

Step 7: Final Verification and Documentation

Torque all hold-down bolts to the manufacturer’s specification using a star pattern. Then re-measure the alignment. Bolt tightening alone can shift the gearbox position enough to push a high-speed output shaft out of tolerance.

Save the alignment report from the laser system. This baseline becomes the reference for future maintenance checks and makes it possible to track alignment drift over time. Reconnect piping and conduit after the final reading. If the alignment shifts after reconnection, pipe strain is present and must be corrected before the unit runs.

With the procedure complete, the next question is: what tolerances should you target?

Alignment Tolerances for Speed Increasers by Output RPM

Alignment tolerances get tighter as shaft speed increases. For a speed increaser, always match tolerances to the output shaft RPM, not the input speed. This single distinction is the most common alignment mistake on speed increaser installations.

Tolerance Reference Table by Output RPM

The table below shows recommended maximum values for offset and angularity at different output shaft RPMs. A unit with 1,750 RPM input and a 3:1 ratio should be aligned to the 5,250 RPM row, not the 1,750 RPM row.

Output Shaft RPM	Max Offset (mils / mm)	Max Angularity (mils/inch / mm/100mm)
Up to 1,200	4.0 / 0.10	1.0 / 0.10
1,200 to 1,800	3.0 / 0.08	0.7 / 0.07
1,800 to 3,600	2.0 / 0.05	0.5 / 0.05
3,600 to 7,200	1.0 / 0.03	0.3 / 0.03
Above 7,200	0.5 / 0.01	0.2 / 0.02

These are acceptable tolerances based on general industry practice. Always defer to the gearbox manufacturer’s specifications when available. ANSI/ASA alignment standards and AGMA 9000 series guidelines provide added reference points.

Hitting half these values is considered excellent alignment and will extend the life of bearings, seals, and couplings. Many modern laser alignment systems include built-in tolerance tables that auto-populate when you enter the shaft RPM. These are typically based on ANSI/ASA standards and serve as a reliable starting point.

What Happens Outside These Tolerances

Operating outside these limits starts a predictable chain of damage. Bearings develop pitting and spalling, seals begin leaking as the shaft runs off-center, and coupling elements fatigue from cyclic loading.

For speed increasers running above 3,600 RPM, being close to the tolerance boundary is not enough. Target the excellent range for any application where unplanned downtime carries a high cost.

Industry-Specific Tolerance Requirements

For applications governed by API standards, such as oil and gas or petrochemical installations, the required tolerances may be even tighter than the general table above. Always check the applicable specification for the installation before setting your targets.

Troubleshooting Common Speed Increaser Alignment Issues

Even with the right tolerances and a solid procedure, some installations present issues that need extra attention. Here are three of the most frequent problems and how to address them.

Alignment Shifts During Bolt Torque

If the alignment reading changes every time you tighten a hold-down bolt, soft foot has not been fully corrected. Return to Step 2 and re-shim.

On speed increasers with asymmetric foot layouts, which are common on right-angle or offset output shaft designs, the gearbox housing may flex unevenly during torque. The laser system’s soft foot check will identify which foot is causing the problem. Correcting it sometimes requires machining the mounting pads or the baseplate to achieve full contact.

Multi-Coupling Machine Train Alignment

When a speed increaser sits between a motor and a driven machine like a pump, compressor, or generator, two couplings need alignment. Start by aligning the speed increaser to the fixed driven machine, then align the motor to the speed increaser input shaft.

Moving the speed increaser to correct one coupling will shift the other. Some laser alignment systems offer machine train programs that measure all couplings in a single setup and calculate corrections for the entire train at once. This is the most effective approach for multi-coupling installations.

Alignment Drift After Initial Commissioning

It is common for a newly installed speed increaser to show slight alignment drift after the first 24 to 48 hours of operation. Foundation settling, gasket compression, and thermal cycling during break-in all contribute to this shift.

Schedule a re-check after the first run period and again after one month. After that, include alignment verification in your preventive maintenance schedule, typically every 6 to 12 months or whenever vibration levels increase.