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How to Use a Rotary Table

Guide · Updated October 28, 2026

A rotary table turns a part on a precise axis under the mill spindle. You use it to cut arcs and radii, mill round bosses, and drill holes on a bolt circle without calculating X-Y coordinates for every hole.

Need hole coordinates instead?

Use the free bolt circle calculator for X-Y positions, or the Gage Block Calculator for setup stacks.

Step by step

Mount and square: Clamp the rotary table to the mill table, and indicate a slot or the side of the body parallel to X if you will cut straight features too.
Center the table: Put an indicator in the spindle and sweep the center bore of the rotary table. Move X and Y until the reading stays still as you rotate the table. Zero the DROs or dials here.
Center the part: Mount the part with a centering plug or indicate its bore or OD while turning the rotary table, and shift the part until it runs true.
Read the dial: Most tables are 90:1 — one handwheel turn is 4°. Read degrees on the table, minutes on the handwheel collar, and seconds on the vernier if fitted.
Offset for radius: Move the table in X or Y by the radius you need (minus or plus the cutter radius for an arc) and lock that axis.
Cut or drill: Rotate to each angle and drill, or feed slowly by the handwheel to cut an arc. Lock the table for drilling; unlock it for arc cuts.
Take up backlash: Always approach each angle turning the same direction so worm backlash does not shift the position.

Worked example: 6 holes on a 3 in bolt circle

With the table and part centered, move the X axis 1.500 in (the radius). Holes are 360 ÷ 6 = 60° apart. On a 90:1 table that is 15 full handwheel turns per hole. Drill at 0°, 60°, 120°, 180°, 240° and 300°, always turning clockwise.

Cutting arcs

For an outside radius R with an end mill of diameter D, offset R + D/2. For an inside radius, offset R − D/2. Climb versus conventional direction matters on a manual table — feed against the cutter rotation to avoid grabbing.

Dividing plates

For odd divisions like 7 or 13, a dividing plate on the handwheel lets you count holes instead of reading degrees. Turns per division = gear ratio ÷ divisions; for 90:1 and 7 divisions, 12 6/7 turns.

Tips

Tram first: tram the mill so arcs cut square.
Center with a dial indicator or the bore indicating method.
Find edges for a reference with an edge finder.
Lock the table for drilling and tapping; see drilling speeds and feeds.

FAQ

What is a rotary table used for?

Cutting arcs and radii, milling round features, drilling bolt circles and indexing parts to precise angles on a milling machine.

How do you center a rotary table under the spindle?

Sweep the table's center bore with an indicator in the spindle and adjust X and Y until the needle does not move as the table rotates.

What is the gear ratio of a rotary table?

Most are 90:1 (4° per handwheel turn); some small tables are 72:1 or 40:1. Check the handwheel collar or the manual.

How do I drill a bolt circle with a rotary table?

Center the table and part, offset one axis by the bolt circle radius, then rotate 360 ÷ number of holes between each hole.

How do I avoid backlash on a rotary table?

Approach every position turning the handwheel in the same direction, and lock the table before drilling.

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