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How to Cut a Radius with a Rotary Table

Guide · Updated October 28, 2026

A rotary table lets a manual mill cut true arcs: center the spindle on the table, move the radius distance away, and rotate the part past the cutter. The offset is the part radius plus or minus the cutter radius.

Check the radius

Check with a radius gage or measure across features with blocks. The free Gage Block Calculator builds the stack.

Step by step

  1. Center the table: Indicate the bore of the table and zero the DRO or dials.
  2. Locate the part: Indicate the arc center on the part over the table center.
  3. Compute the offset: Outside radius: R + cutter radius. Inside radius: R − cutter radius.
  4. Move out: Move the table that distance in X or Y and lock it.
  5. Set the start and end angles: Mark the start and stop angles on the table dial.
  6. Cut in steps: Rotate at a steady rate, taking depth in passes.
  7. Blend: Light finish pass and check.

Worked example

Cut an outside 1.000 in radius with a 1/2 in end mill: offset = 1.000 + 0.250 = 1.250 in from table center. For an inside 1.000 in radius with the same cutter: 1.000 − 0.250 = 0.750 in. If the arc spans 90° and you need 0.010 in for a finish pass, rough at 1.260 in, then finish at 1.250 in. Rotate against the cutter rotation (conventional) to avoid the table being pulled.

Tangent blends

Straight edges that meet an arc must end exactly on the tangent point. Mill the straight sections with the table locked at the arc start and end angles so they blend.

Common problems

A step at the blend means the center was off. Wrong radius means the cutter diameter was wrong or the offset sign flipped. Chatter means unlocked axes.

Tips

Worked example: 1.000 in radius with a 0.500 in end mill

To cut an outside 1.000 in radius with a 0.500 in end mill, offset the spindle from the table center by R + r = 1.000 + 0.250 = 1.250 in. For an inside radius, use R − r = 0.750 in. Rotate the table slowly and climb-mill the finish pass.

Check the radius with a radius gage; a gap at one end usually means the table was not centered under the spindle.

FAQ

What is the offset for an outside radius?

Part radius plus cutter radius.

For an inside radius?

Part radius minus cutter radius.

Which way to rotate?

Usually conventional to avoid the cutter pulling the table.

Do I lock the axes?

Yes, lock X and Y while rotating.

How do I center the table?

Indicate the table bore.

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