Magnetic Assemblies / Pot Magnets
Pot Magnets: Compact Steel-Cup Holding Systems
Pot magnets combine a permanent magnet with a ferromagnetic cup to concentrate flux at one working face. Selection should be based on the real contact surface, air gap, load direction and mounting method—not a catalogue pull-force number alone.
Geometry and Dimension Definition
Use functional datums and define the magnetization reference on the drawing. The table below provides the minimum geometry information for a practical manufacturing review.
| Parameter | How to define it | Why it matters |
|---|---|---|
| D — Cup diameter | Finished outside diameter | Defines contact area and installation envelope |
| H — Overall height | Cup, magnet and any boss or thread | Controls recess depth and mechanical clearance |
| Mounting interface | Countersunk hole, internal thread, stud or plain back | Transfers the external load into the structure |
| Working face | Flatness, coating and exposed pole arrangement | Controls the effective air gap and holding force |
Design Considerations
Steel-cup magnetic circuit
The cup redirects return flux to the working face and protects the magnet, but cup thickness and steel grade must avoid saturation.
Rated pull force
Force data should state steel thickness, surface finish, loading direction and test method. Thin or painted steel can reduce performance sharply.
Mounting and load path
The screw or thread should carry service loads without placing tensile or bending stress into the brittle magnet.
Manufacturing and Assembly Notes
- Side loads are much lower than direct pull unless a mechanical stop is provided.
- An air gap from paint, dirt, curvature or roughness reduces holding force.
- Over-tightening a countersunk fixing can damage the magnet or distort the cup.
- Impact attachment can chip the exposed magnetic face.
Typical Applications
Fixtures and jigs
Compact removable holding points for production equipment.
Doors and access panels
Reliable closures with a defined steel target.
Sensors and lighting
Threaded or countersunk mounting for repositionable devices.
Retail and display systems
Reusable attachment without drilling the target surface.
Engineering Questions
Why is a pot magnet stronger than the bare magnet?
The steel cup concentrates usable flux at one face and provides a low-reluctance return path. The improvement depends on cup design and the target steel.
Why is real-world holding force lower than the catalogue value?
Air gaps, thin steel, side loading, surface curvature and incomplete contact all reduce force. Test the complete joint.
Can a pot magnet work at elevated temperature?
Yes, with a suitable magnet grade, adhesive and coating. Rate the complete assembly, not only the NdFeB material.
Should I choose a stud, thread or countersunk hole?
Choose the interface from installation access, load direction, serviceability and allowable tightening torque.
For a focused design review, share your drawing, operating temperature, air gap, target magnetic performance and annual volume through our enquiry page. You can also return to Magnetic Assemblies for material-level guidance.