A rotary table is a machine tool accessory that clamps to a drill press, milling machine, or workbench and holds a workpiece while rotating it around a vertical axis. You set it up by centering it under the spindle, locking it to the table, and zeroing a reference point. Indexing means rotating the table by a fixed, repeatable angle to machine evenly spaced features. This guide covers the practical setup steps and the indexing math that matters in a home shop.
What Is A Rotary Table And What Is It Used For?
A rotary table is a circular, graduated workholding device with a rotating platter mounted on a base. The platter has T-slots or a chuck for clamping parts, and a handwheel or motor turns it through precise angles. Most manual tables read in degrees on a graduated collar, often with a vernier for finer resolution.
It solves one basic problem: machining features that sit around a circle. Bolt-hole patterns, curved slots, arcs, and radial cuts are hard to lay out and drill freehand. On a rotary table you clamp the part once, then rotate to each position and cut. The spacing comes from the table’s graduations, not from your layout skill.
Common uses include drilling evenly spaced holes on a bolt circle, milling arcs and rounded corners, cutting gear teeth and splines, and machining circular pockets. It also lets you rotate a part under a fixed cutter to produce a curved surface that a straight X-Y feed cannot make.
How Do You Set Up A Rotary Table On A Mill Or Drill Press?
Setup is the part that decides whether your cuts land where you want them. The table must be centered under the spindle and locked down solidly before you trust any angle reading.
- Mount the table. Bolt or clamp the rotary table to the machine table. On a mill, align it roughly with the table slots first, then refine.
- Center it under the spindle. Chuck a dial test indicator in the spindle and sweep the table’s center bore or a known round feature. Tap the table until the indicator reads near zero all the way around.
- Lock the base. Tighten the mounting bolts once centered. Recheck the indicator; tightening can shift the table slightly.
- Set your zero. Rotate to a reference feature or the scale zero and lock the table’s rotation lock. This is your starting angle for indexing.
- Clamp the work. Mount the part so it sits flat and secure. Any part movement during a cut throws off every subsequent position.
On a drill press the same centering logic applies, though you are usually working to coarser tolerances. Center the table under the chuck with an indicator if you have one, or use a centering pin in the chuck to align the table’s bore.
A non-obvious point: many hobbyists skip the indicator sweep and eyeball the center. That works for rough work but not for anything where holes must line up with a mating part. The centering error shows up as a wobble in your bolt circle, and it grows with the radius.
How Do You Index A Rotary Table For Evenly Spaced Features?
Indexing means dividing a full turn into equal steps. The math is simple: divide 360 degrees by the number of features you need. For 6 holes, each step is 60 degrees. For 8 holes, each step is 45 degrees. For 12 holes, each step is 30 degrees.
Turn the handwheel by that amount, lock the table, machine the feature, unlock, and repeat. The table’s graduated collar shows you the angle directly, so you do not need to calculate fractions in your head each time.
For features that do not divide evenly into 360, you still work in degrees. A feature every 37.5 degrees, for example, is a valid step; you just read it off the collar. The key is consistency, not round numbers.
Some tables use a dividing-plate or sector system for very fine or unusual divisions. That is more common on dedicated rotary tables and indexing heads than on basic hobby tables. If your table has one, follow its chart rather than doing the arithmetic by hand.
What Is The Difference Between Indexing And Rotary Milling?
Indexing means stopping at fixed positions and cutting while the table is locked. Rotary milling means feeding the table continuously while the cutter is engaged, so the part rotates through an arc as material is removed.
Use indexing for discrete features: bolt holes, slots, gear teeth, keyways. Use rotary milling for continuous curves: arcs, fillets, circular pockets, and rounded profiles. The two are not competing methods; they cover different jobs.
For rotary milling, you control the feed by turning the handwheel steadily, or by using a power feed if the table has one. A steady, even feed produces a cleaner arc than a jerky one. Lock the table only after the cut is complete.
How Accurate Is A Rotary Table And What Affects Accuracy?
A typical manual rotary table is graduated in whole degrees, often with a vernier that lets you read to a fraction of a degree. The actual accuracy you achieve depends on several things beyond the scale.
- Centering error. If the table is not centered under the spindle, features drift off the intended circle. This is usually the largest error source.
- Backlash. The handwheel and worm gear have some play. Always approach a setting from the same direction so backlash does not throw off your angle.
- Workholding rigidity. A part that shifts under cutting force ruins the position no matter how well you set the table.
- Table condition. Worn worm gears and loose locks introduce play. Keep the table clean and adjusted.
For most home-shop work, a well-centered table with consistent approach direction gives results good enough for mating parts and fixtures. For precision work, verify with a dial indicator rather than trusting the scale alone.
What Common Mistakes Should You Avoid?
The most frequent error is trusting the scale without centering the table first. A perfectly graduated table that is off-center produces a wobbly pattern. Center first, then index.
Second is forgetting backlash. If you overshoot a setting and back up, the handwheel reads the new angle but the table may not have moved the full amount. Always finish a setting by turning in the same direction.
Third is inadequate clamping. A part that looks secure can creep under a milling cut. Check it before every pass, especially on interrupted cuts.
Fourth is skipping the lock. Some tables have a rotation lock; leaving it loose lets vibration move the table mid-cut. Lock before cutting, unlock before indexing.
Fifth is ignoring the table’s own setup. A rotary table that is not level or not bolted flat will flex and shift. Mount it solidly and check it is seated before you center it.
Frequently Asked Questions
How do you calculate indexing on a rotary table?
Divide 360 degrees by the number of equal features you need, then turn the handwheel by that amount for each step. For example, 8 holes means a 45-degree step between each.
Do you need a dial indicator to set up a rotary table?
A dial indicator is the reliable way to center the table under the spindle, and it is strongly recommended for any work where features must align. You can work without one for rough jobs, but centering error will show up in the finished pattern.
What is the difference between indexing and rotary milling?
Indexing locks the table at fixed angles to cut discrete features like bolt holes. Rotary milling feeds the table continuously to cut arcs and curves.
Why does my rotary table pattern come out uneven?
The most common cause is a table that is not centered under the spindle, which makes features drift off the intended circle. Backlash and loose workholding can also throw off positions.
