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Magnetic Chuck Basics
Guide · Updated October 28, 2026
A magnetic chuck holds steel parts flat for surface grinding. It is fast and accurate, but small parts, thin parts and non-magnetic materials need some tricks.
Check parallel
Check ground parts for parallelism with an indicator on a plate and gage blocks. Check it with a mic you've verified against gage blocks; the free Gage Block Calculator builds the stack.
Step by step
- Clean everything: Wipe the chuck and part and stone off burrs; a chip under the part ruins parallelism.
- Cover the poles: Place the part so it spans several pole lines; a part on one pole holds weakly.
- Block small parts: Surround small or tall parts with steel blocks or parallels so they cannot slide or tip.
- Engage: Turn on the chuck and push the part to check it is held.
- Grind light: Take light passes, and flip thin parts to grind both sides.
- Release and demag: Turn off the chuck and demagnetize the part before measuring.
- Stone the chuck: Stone the chuck face after use, and grind it in place only when it is out of flat.
Worked example
0.125 in thick 1018 plate bowed 0.002 in: put it on the chuck with the hump up and shim under the low ends with paper so the magnet does not pull it flat. Grind until it cleans up, flip, remove the shims and grind the other side in light 0.0005 in passes, flipping a couple of times. Finish at 0.123 in with both sides parallel within 0.0002 in.
Thin parts warp
The magnet pulls a bowed part flat, you grind it, and it springs back when released. Shim it, use light passes, flip often and use coolant to keep heat down.
Non-magnetic parts
Aluminum, brass and stainless (300 series) will not hold. Use a vise on the chuck, double-sided tape on a steel plate, or blocks clamped around the part.
Tips
- Dress the wheel first: dressing a grinding wheel.
- Use parallels and setup blocks for blocking.
- See grinding speeds and feeds.
- Measure on a surface plate.
FAQ
Permanent or electromagnetic chuck?
Permanent chucks are simple and common on manual grinders; electro chucks have adjustable hold and built-in demag.
Why won’t my part hold?
It is too small, does not cover the poles or is not magnetic.
How do I grind thin parts on a mag chuck?
Shim the bow, take light passes and flip often.
Do I need to demagnetize parts?
Yes, or chips stick and indicators drag.
Should I grind my magnetic chuck?
Only when it is out of flat, with light passes and the chuck switched on.
Related guides and calculators
- How to Dress a Grinding Wheel
- Grinding Speeds and Feeds
- Parallels and Setup Blocks Basics
- Flatness and Parallelism Checks with Gage Blocks
- How to Use a Surface Plate
- Surface Finish Basics
- How to Use a Surface Grinder
- How to Use a Spin Indexer
- How to Use a Compound Sine Plate
- How to Use a Toolmaker's Vise
- How to Use a Magnetic Sine Chuck
- All free machinist calculators
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