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3mm motor shaft is a relatively common shaft diameter found in micro-motors and small brushless motors. In Hall encoders, magnetic encoders, FOC brushless motors and speed measurement systems, multi-pole magnetic rings are frequently used in conjunction with them. Today, we would like to recommend some dimensions for multi-pole magnetic rings with a 3mm bore.
Based on current application experience within the motor and magnetic encoder industries, multi-pole magnetic rings compatible with 3 mm motor shafts typically have an outer diameter of 6 mm to 12 mm. The inner bore of the magnetic ring is usually slightly larger than the 3 mm shaft diameter to facilitate assembly; in practical design, this is generally maintained at approximately 3.02 to 3.1 mm, with the final tolerance determined by the method of installation—whether by interference fit, adhesive bonding or press-fitting.
If installation space is limited, we recommend selecting smaller magnetic rings with an outer diameter of 6–7 mm, which can meet the speed measurement requirements of most micro-motors. If higher angular resolution is required, magnetic rings with an outer diameter of 8–12 mm can be chosen, and the number of poles increased to enable the Hall sensor or magnetic encoder to obtain a more stable and precise magnetic field signal. For standard speed measurement applications, 4 or 6 poles are sufficient. However, high-precision applications such as encoders and motor closed-loop control require a higher number of poles.
Recommended sizes for multi-pole magnetic rings compatible with 3 mm motor shafts
Regarding material selection, if the operating environment is at a high temperature or cost is a key consideration, sintered ferrite multi-pole magnetic rings or injection-moulded ferrite multi-pole magnetic rings may be selected. If a stronger magnetic field and smaller size are required, bonded neodymium-iron-boron multi-pole magnetic rings or injection-moulded neodymium-iron-boron multi-pole magnetic rings are recommended.
Examples of some multi-pole magnetic rings with a 3 mm bore;
D12 × d3 × 5 mm / Radial 2-pole / Y10
D25 × d3.175 × 18 mm / 25-degree oblique 2-pole magnetisation
D6.5 × d3 × 3.7 mm / External 8-pole / 2200 Gs / D-shaped inner bore
D6 × d3 × 12 mm / OD 4-pole
3mm Square Hole Ferrite Planar 2 Pole 4 Pole Magnet Ring
D14 × d3.14 × 4 mm / Radial 26-pole
4 pole plastic injection molded ferrite magnets 9.5 x 3.15 x 3 mm
Radial 8 pole small magnetic ring OD 8mm x 3.175mm x 3mm
D16 × d3.1 × 2.5 mm / Single-sided 6-pole
D14.6 × d3.1 × 2.8 mm / Axial magnetisation, 4-pole
If you have specific dimensions, product applications or require samples, please feel free to contact us; we offer custom moulding services.
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