Custom arc-segment magnets for motor rotors

Start with the rotor drawing

Send the magnet drawing, its revision and the intended motor application. Define the inner and outer radii, arc angle, axial length and inspection datums. Mark the dimensions that control fit, adhesive clearance and assembly. Include the number of segments per rotor, sample quantity and expected annual demand.

An existing part number is enough to open the discussion. Our magnet specification guide lists the information needed to compare production routes against the same requirement.

Specify orientation separately from shape

An arc shape does not establish its magnetisation. A segment cut from a uniformly oriented block can retain a parallel direction throughout the material. In a true radial segment, the orientation follows the radius across the arc. True radial sintered NdFeB requires suitable pressing tooling and a magnetising fixture; feasibility depends on the geometry.

Mark the direction, polarity reference and required delivery state on the drawing. For a set with different orientations, identify each position. Our magnetisation guide explains the terminology; Bunting illustrates the distinction between parallel and true radial arcs.

Agree finished dimensions and protection

State whether the drawing dimensions apply after coating. Coating thickness belongs in the fit calculation, alongside the adhesive layer and assembly clearance. Specify edge breaks, critical surfaces and the inspection method where these affect acceptance.

We review tolerances against the proposed production route. The coating should suit the exposure, bonding process and assembly temperature. Nickel-based finishes and epoxy systems have different bonding and protection characteristics; selection depends on the complete coating system. Goudsmit’s coating guide outlines these differences.

Choose the grade for the operating point

A grade designation is a starting point. Share the temperature range, short peaks, opposing magnetic field and required magnetic properties. Where available, include the operating point and demagnetisation curves used in the motor design.

Review NdFeB grades against those conditions. Coercivity, remanence, geometry and the magnetic circuit all matter when comparing alternatives. Arnold’s NdFeB reference explains grade properties and temperature considerations.

From samples to a qualified second source

EMTXI compares suitable routes on feasibility, technical deviations, sample and production prices, minimum order quantity and lead time. Measurement and acceptance requirements are agreed before qualification samples are ordered. You evaluate the samples in your application; we coordinate the documentation and the route towards recurring supply.

For an additional supplier, the qualification process establishes what must match the existing requirement and how proposed differences will be assessed. Origin and any export-licence requirements are addressed alongside the technical and commercial comparison.

Buyer questions

Can you quote a magnet currently bought elsewhere?

Yes. Send the drawing or specification and the properties that must be maintained. You do not need to name your current supplier. We can arrange an NDA before drawings or prices are shared.

Can segments be supplied as matched sets?

Matched sets sorted by flux can be included in the enquiry. State the acceptance limits, measurement arrangement and temperature. We confirm the proposed sorting specification with the supply route before quoting.