Medical

Medical

Balance Technology Inc. builds balancing machines and measurement systems for medical device manufacturing: surgical and dental handpiece rotors, centrifuge rotors, imaging gantry assemblies, pump rotors, small motor armatures, and ventilator and compressor blowers. BTI has been designing this equipment in Whitmore Lake, Michigan since 1968. Medical rotating components are mostly small and mostly fast. That combination drives the balancing problem: a rotor weighing a few hundred grams at fifty thousand rev/min produces forces that a much heavier, slower part never sees, and the tolerance tightens accordingly. Machines for this work are specified around measurement resolution and fixturing repeatability rather than around load capacity.

What BTI Balances in Medical Devices

BTI balancing machines are built on four platforms (VNR (vertical non-rotator), H (horizontal cradle), VR (vertical rotator) and P (platform suspension)) plus spinners and test stands. The platform follows the part geometry and how it has to be held; the correction method follows the material and where there is room to add or remove mass.

Component	Typical platform	Correction method
Surgical handpiece and drill rotors	VR, spinner	Grind, mill
Dental handpiece turbines	Spinner, VR	Grind
Centrifuge rotors	VNR, P	Drill, weight-add
Imaging gantry and rotating assemblies	P	Weight-add
Blood, infusion and peristaltic pump rotors	VR	Mill, weight-add
Small motor armatures and rotors	H, VR	Mill, weight-add
Ventilator and compressor blowers	VNR, VR	Drill, weight-add

How a Machine Gets Sized

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. 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. A shop that needs one machine to cover a wide range of parts, and does not need tight repeatability, can run a much broader weight range on a given class than a production program can. Tell BTI the part weight and BTI will name a class the same day. See BTI machine platforms for the full platform and class architecture.

Balance Grade and Tolerance

Medical rotors run at service speeds well above most industrial equipment, so grades sit at the tight end of the scale. Balance tolerances are set by ISO 21940-11, which superseded ISO 1940-1. The standard assigns a balance quality grade G, 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 6.3	Pump rotors, blowers, normal electric armatures
G 2.5	Small high-speed motor rotors and precision drives
G 1	Precision spindles and handpiece rotors
G 0.4	The tightest grade in the standard, for precision grinder spindles

Work out a specific tolerance with the ISO balance tolerance calculator.

Small Rotors and High Service Speeds

Permissible residual unbalance scales with rotor mass and falls as service speed rises. A small rotor at high speed therefore lands at a residual unbalance figure small enough that fixture repeatability, not the measurement system, becomes the limiting factor. Getting that right is a tooling problem before it is a machine problem. BTI concepts the fixture from the part print, so the holding method, the drive and the correction access are settled together rather than in sequence. Where a part cannot tolerate material removal (a finished or coated surface, or a sterile assembly) correction moves to weight-add or to a balancing operation earlier in the build.

Correction Methods

Method	Where it fits
Grind	Hardened and finished surfaces, including handpiece rotors
Mill	Controlled removal on a defined correction band
Drill	Components with material available to remove
Weight-add	Assemblies where removal is not permitted by the part print
Adhesive and applied weight	Plastics, coated parts and finished assemblies

Standards

BTI certifies machines to ISO 21940, SAE International balancing specifications, and DIN specifications. Where a program carries a measurement system capability requirement, BTI evaluates the part and the process first, then confirms what is achievable and commits to it in the machine specification.

Frequently Asked Questions

Browse BTI balancing machines or request a quote.