In This Article
Key Takeaways
- ◆Manufacturing tolerance depends on geometry, process, feature and measurement method.
- ◆The material easy axis need not be the press direction; identify the actual orientation route.
- ◆Use finished coated dimensions where they control assembly fit.
- ◆The radial-ring TDS, Rev A of 31 July 2026, states OD 20 to 75 mm, ID 15 to 68 mm, wall 2 to 7 mm and height 5 to 50 mm, with ±0.05 mm standard dimensional tolerance within the qualified route. These limits are not freely combinable. Confirm the drawing, grade, pole pattern and individual features before quotation. The separate integrated-Halbach route states ±0.02 mm on critical features, subject to feature and drawing confirmation.
- ◆No universal cost or delivery penalty follows from a tolerance number alone.
Confirm the manufacturing route
Sintering, machining and coating each affect dimensions. The achievable tolerance depends on size, shape, material and feature. Do not apply a single industry-wide tolerance table to every magnet. The radial-ring TDS, Rev A of 31 July 2026, states OD 20 to 75 mm, ID 15 to 68 mm, wall 2 to 7 mm and height 5 to 50 mm, with ±0.05 mm standard dimensional tolerance within the qualified route.
These limits are not freely combinable. Confirm the drawing, grade, pole pattern and individual features before quotation. The separate integrated-Halbach route states ±0.02 mm on critical features, subject to feature and drawing confirmation.
Distinguish pressing from material orientation
Pressing direction and magnetic alignment direction depend on the process and need not coincide. Sintering shrinkage is process-specific. Mark the material orientation and intended magnetization on the drawing rather than deriving them from a generic shrinkage percentage. The dimension most important to the air gap or retention must come from the assembly design.
Qualify surface preparation
Agree surface finish, cleanliness and preparation with the coating and adhesive process. No universal Ra value is optimal for every adhesive. Test the joint on the specified coated or bare substrate. The AA 326 adhesive correction is detailed in the segmentation guide.
Include coating in the dimensions
State whether the dimensions apply before or after coating. If two opposed faces each receive a specified 10 µm layer, the nominal overall dimension grows by 20 µm; actual coating variation also belongs in the tolerance stack. This is a geometry example, not a standard coating thickness. Specify the coating formulation, thickness on each face, edge coverage, substrate preparation and cure.
Agree a corrosion test method, exposure duration and acceptance endpoint for the actual part, then request its report. Salt-spray hours are not a service-life guarantee.
Write the inspection requirement
Identify critical features and functional datums. State the measuring method, uncertainty needs, sampling plan, magnetic acceptance and traceability. Mark reference dimensions clearly. Agree the acceptance records and how a nonconforming part is handled before the first sample.
Compare the cost of each option
Ask for quotations for functionally acceptable alternatives. Include machining, fixturing, coating and inspection. Do not promise a fixed percentage saving, reject rate or delivery reduction from loosening a dimension. Retain the tolerances needed for magnetic performance, retention and assembly.
Frequently Asked Questions
What is the standard magnet tolerance?
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Sintering, machining and coating each affect dimensions. The achievable tolerance depends on size, shape, material and feature. Do not apply a single industry-wide tolerance table to every magnet. The radial-ring TDS, Rev A of 31 July 2026, states OD 20 to 75 mm, ID 15 to 68 mm, wall 2 to 7 mm and height 5 to 50 mm, with ±0.05 mm standard dimensional tolerance within the qualified route. These limits are not freely combinable. Confirm the drawing, grade, pole pattern and individual features before quotation. The separate integrated-Halbach route states ±0.02 mm on critical features, subject to feature and drawing confirmation.
How tight can a feature be made?
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Confirm the specific feature, geometry, process and measurement capability with the supplier. A published tolerance on another route is insufficient.
Should dimensions include coating?
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State whether the dimensions apply before or after coating. If two opposed faces each receive a specified 10 µm layer, the nominal overall dimension grows by 20 µm; actual coating variation also belongs in the tolerance stack. This is a geometry example, not a standard coating thickness. Specify the coating formulation, thickness on each face, edge coverage, substrate preparation and cure. Agree a corrosion test method, exposure duration and acceptance endpoint for the actual part, then request its report. Salt-spray hours are not a service-life guarantee.
Is the press axis always the magnetization axis?
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Pressing direction and magnetic alignment direction depend on the process and need not coincide. Sintering shrinkage is process-specific. Mark the material orientation and intended magnetization on the drawing rather than deriving them from a generic shrinkage percentage. The dimension most important to the air gap or retention must come from the assembly design.
How do I reduce machining cost?
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Ask for quotations for functionally acceptable alternatives. Include machining, fixturing, coating and inspection. Do not promise a fixed percentage saving, reject rate or delivery reduction from loosening a dimension. Retain the tolerances needed for magnetic performance, retention and assembly.
Send the drawing and functional tolerance requirements to confirm the manufacturing and inspection route.