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How to Use a Magnetic Sine Chuck

Guide · Updated October 28, 2026

A magnetic sine chuck is a sine plate with a magnetic top. Set the angle with gage blocks under the roll, switch on the magnet and grind the angle.

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Step by step

  1. Clean: Clean chuck and blocks.
  2. Calculate: Stack = L × sin θ.
  3. Set: Place the stack under the roll.
  4. Lock: Lock the hinge.
  5. Hold the part: Use a stop on the low side.
  6. Grind: Grind lightly.
  7. Check: Check the angle with a sine bar.

Worked example

A 5 in chuck at 30°: 5 × sin 30° = 2.5000 in. At 22.5°: 5 × 0.38268 = 1.9134 in.

Stops

Use a stop plate on the low side so the part cannot slide down.

Heat

Grind lightly; heat changes angle and size.

Worked example: grinding a 15° bevel to a line

A 5.000 in sine chuck: stack = 5 × sin 15° = 5 × 0.258819 = 1.2941 in,; the calculator gives a real block combination. Grind until the bevel meets the scribed line, taking 0.0005 in passes. Check the finished angle on a sine bar: the indicator should read the same at both ends of the bevel.

Angle sensitivity

On a 5 in chuck, angle error ≈ stack error ÷ (5 × cos θ) radians. At 15°, a 0.0001 in stack error is 0.0001 ÷ (5 × 0.9659) = 0.0000207 rad, about 4.3 arc seconds. Clean blocks matter more than the last decimal.

Setting zero

With no stack, the top should be parallel to the base. Check it by sweeping the top with an indicator before you set any angle; any error at zero adds to every angle.

Common problems

Part slides: no stop. Wrong angle: wrong roll length. Burn: too heavy.

Worked example: 15° and 30° on a 5 in chuck

Stack height H = L × sin θ. With L = 5.000 in: 15° needs 5 × 0.25882 = 1.2941 in; 30° needs 5 × 0.50000 = 2.5000 in. A 1.2941 stack can be 1.0000 + 0.1500 + 0.1441 or similar from an 81-piece set; let the calculator pick the fewest blocks.

How much does a stack error matter?

The angle error is roughly ΔH ÷ (L × cos θ) radians. A 0.0001 in stack error at 15° on a 5 in chuck: 0.0001 ÷ (5 × 0.9659) = 0.0000207 rad, about 4.3 arc-seconds. A burr or chip under a roll does far more damage than block grade, so clean the rolls and the stack seat before every setup.

More common problems

Part slides at steep angles: magnetic hold drops on thin or small parts, so add a stop or back plate against the downhill edge. Angle reads wrong after grinding: the chuck was not indicated to the wheel travel before tilting. Hinge play: check by indicating the top plate while pushing it sideways; any movement shows up as angle scatter.

Tips

Fuller worked example: 15° on a 10 in sine chuck

For a 10 in sine chuck at 15°, the stack is H = 10 × sin 15° = 10 × 0.25882 = 2.5882 in. From an 81-piece set: 0.1002 + 0.138 + 0.350 + 2.000 = 2.5882 in.

After grinding, check the angle on a sine bar or plate with an indicator. A 0.0005 in change over 2.000 in of travel is an error of about 0.0005 ÷ 2 = 0.00025 rad, or 0.014°.

FAQ

What is a sine chuck?

A magnetic sine plate.

What is the stack for 30° on 5 in?

2.5000 in.

Why use a stop?

To stop the part sliding.

How do I check the angle?

Sine bar and gage blocks.

Why grind lightly?

To avoid heat.

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