Balancers

Manual, Semi-Automatic & Automatic Balancing Machines | BTI

BTI engineers and manufactures a complete line of manual, semi-automatic, and fully automatic industrial balancing machines, all part types, production rates, and levels of automation. From static to dynamic, single-plane to multi-plane, hard-bearing to soft-bearing, and single-station to multi-station, BTI does it all.

What a Balancing Machine Does

A balancing machine measures the unbalance in a rotating part and tells you how much mass to add or remove, and where, to bring it inside tolerance. Unbalance exists when a rotor’s mass is not distributed symmetrically about its rotational axis. Spin that rotor and the offset mass produces a centrifugal force that rises with the square of rotational speed — double the speed and the force quadruples. That force is what shortens bearing life, loosens fasteners, fatigues mountings and produces the noise and vibration an operator feels. Balancing is the process of measuring it and correcting it, and a balancing machine is the instrument that makes the measurement repeatable enough to act on. BTI has been building these machines in Whitmore Lake, Michigan since 1968, for automotive, aerospace, power generation, defense and a dozen other industries.

Static and Dynamic Balancing

The distinction is about correction planes, and it follows from the shape of the part. Static balancing corrects in a single plane. It suits parts that are large in diameter relative to their length — a disc, a flywheel, a fan wheel, a brake rotor, a grinding wheel. For these, one correction plane is enough because the unbalance acts essentially in one plane already. Dynamic balancing corrects in two or more planes. Any part with meaningful length along its axis — a crankshaft, a driveshaft, a motor rotor, a turbine assembly — can carry unbalance that produces a couple as well as a force. Correcting that requires measurement and correction in two planes, which is what a dynamic balancing machine does. If a part is longer than roughly its own diameter, assume dynamic. The ISO balance tolerance calculator takes the number of correction planes as an input for exactly this reason.

Hard-Bearing and Soft-Bearing Machines

Both measure unbalance. They differ in where the machine runs relative to the resonant frequency of its own suspension.

Type	How it works	Where it fits
Hard-bearing	Runs below the suspension’s resonant frequency. Measurement is derived from force, so the machine is calibrated permanently and holds calibration across parts.	Mixed part families, job shops, MRO, low-to-moderate volume with frequent changeover
Soft-bearing	Runs above resonance. Measurement is derived from displacement, so the machine is calibrated per part setup using a known test mass.	Dedicated production of one part family, and very low residual tolerances

The practical difference is changeover. A hard-bearing machine can move from one part to the next without recalibration, which is why it dominates shops running a mixed workload. A soft-bearing machine will generally resolve smaller residual unbalance, which matters when the tolerance is tight enough that the measurement itself becomes the constraint.

Machine Platforms

The platform follows the part geometry and how the part has to be held. The correction method follows the material and where there is room to add or remove mass.

Platform	How the part is held	Typical components
Horizontal cradle (H)	Shaft-type parts supported at their journals	Crankshafts, driveshafts, armatures, rotor assemblies
Vertical rotator (VR)	Parts held and driven about a vertical axis	Torque converters, turbochargers, pump rotors, wheels
Vertical non-rotator (VNR)	Disc-shaped parts measured without full rotation	Brake rotors and drums, flywheels, clutches, fan wheels
Platform suspension (P)	Assemblies carried on a suspended platform	Cooling modules, complete assemblies, irregular parts

There are four platforms. Within them, individual machines take different styles. An overhung configuration is a horizontal cradle arrangement for parts supported at one end rather than between journals. Air-bearing support is a style of horizontal cradle or vertical rotator, used where near-frictionless support is needed to resolve very low residual unbalance. Both are configurations of a platform rather than platforms in their own right. A BTI machine designation names a platform and a class. The number is a class, not a part weight limit — it describes the size and load envelope of the base. See BTI machine platforms for the full architecture.

Levels of Automation

Level	What it does	Where it fits
Manual	Operator loads, runs and corrects. Lowest cost, widest part range.	MRO, remanufacturing, job shops, low volume
Semi-automatic	Machine measures and positions; operator loads and performs correction.	Moderate volume, several part families
Fully automatic	Load, measure, correct and unload without operator intervention, integrated into the line.	Production programs at takt time

Which one fits is driven by required production rate more than by part complexity. A fully automatic machine engineered around one part family is the right answer at volume and the wrong answer for a shop that needs to cover a wide range of parts. Armature balancing is a common case where the deciding factor isn’t volume at all — see the benefits of automated armature balancing for why tight tolerances on small, fast rotors can make manual correction unable to hold the tolerance regardless of production rate.

Balance Tolerance and ISO 21940-11

Balance tolerances are set by ISO 21940-11, which superseded ISO 1940-1. The standard assigns a balance quality grade G by component type, and the permissible residual specific unbalance follows from that grade and the service speed: e_per = (G × 60) ÷ (2π × n) where e_per is permissible residual specific unbalance in g·mm/kg, G is the balance quality grade in mm/s, and n is the service speed in rev/min. Permissible residual unbalance is then U = e_per × m, divided across the correction planes.

Grade	Typical components
G 630	Crankshaft drives of large slow marine diesel engines
G 250	Crankshaft drives of rigidly mounted fast four-cylinder diesel engines
G 100	Crankshaft drives of fast diesel engines with six or more cylinders
G 40	Car wheels, wheel rims and wheel sets
G 16	Driveshafts and cardan shafts with special requirements
G 6.3	Fans, flywheels, pump impellers, normal electric armatures
G 2.5	Gas turbine rotors, turbochargers, machine-tool drives
G 1	Precision spindles and small high-speed rotors
G 0.4	Precision grinder spindles — the tightest grade in the standard

Work out a specific figure with the ISO balance tolerance calculator. BTI certifies machines to ISO 21940, SAE International balancing specifications, and DIN specifications.

Correction Methods

Method	Where it fits
Drill	Cast and forged parts with material available to remove
Mill	Controlled removal on a defined correction band, suited to volume
Grind	Hardened or finished surfaces, including turbine and spindle hardware
Weld-on weight	Driveshafts, torque converters and fabricated assemblies
Clip-on or press-on weight	Wheel and tire assemblies
Adhesive and applied weight	Plastics, coated parts and finished assemblies

Correction is settled when the fixture is concepted from the part print, not afterwards. Where a surface is finished, coated or otherwise cannot be cut, correction moves to weight-add or to an operation earlier in the build.

How a Machine Gets Specified

Sizing works from the tooling and the part together, not the part alone. Tooling is not specified until the part prints are reviewed and the fixture is concepted, and the heavier the tooling-plus-part assembly is relative to the class, the less repeatable the measurement becomes. To quote a balancing machine, BTI needs the part print, the part weight, the service speed, the balance tolerance if one is specified, and the required production rate. Lead times are quoted in weeks at the time of quotation and move with current backlog. Tell BTI the part weight and BTI will name a class the same day.

Rebuilds, Retrofits and Upgrades

A balancing machine that is not performing does not always need replacing. Where the mechanical base is sound, the measurement system and controls can be replaced for a fraction of the cost of a new machine. BTI does this for its own equipment and for machines built by other manufacturers. See BTI rebuilds and retrofits, competitor rebuilds and retrofits, and PC upgrades.

Frequently Asked Questions

What is the difference between static and dynamic balancing?

Static balancing corrects in one plane and suits disc-shaped parts. Dynamic balancing corrects in two or more planes and is required for any part with meaningful length along its axis, because such parts can carry a couple as well as a force. As a rule of thumb, a part longer than its own diameter needs dynamic balancing.

Should I buy a hard-bearing or soft-bearing machine?

Hard-bearing for a mixed part range, because it holds calibration across changeovers. Soft-bearing for dedicated production of one part family, or where the residual tolerance is tight enough that measurement resolution becomes the limiting factor.

How do I know what balance tolerance my part needs?

ISO 21940-11 assigns a balance quality grade by component type and derives the tolerance from service speed and rotor mass. If the part print does not specify one, BTI works it out from the part and the duty.

Can one balancing machine handle more than one part?

Yes, within a class. How wide that range can be depends on the tooling and on how much repeatability the application requires. MRO and remanufacturing shops routinely run a broad part range on a single machine.

Does BTI service balancing machines made by other manufacturers?

Yes. Where the mechanical base is sound, BTI rebuilds and retrofits competitor equipment as well as its own.

What information does BTI need to quote a balancing machine?

The part print, the part weight, the service speed, the balance tolerance if specified, and the required production rate. See balancing machines by industry or request a quote.