CNC turntable selection: match the table to the part, not the brochure

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  Key takeaways
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  Which CNC turntable type fits which job
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  Why CNC turntable selection starts with a face map
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  Load, torque and the numbers that decide accuracy
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  Brake type, drive type and thermal drift
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  When a turntable is the wrong answer
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  What to ask a shop before you send the file
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  How GreatLight handles rotary work
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  Step by step: qualifying a rotary table job

Before you compare brands, draw the part and mark every face that needs machining. Count how many of those faces sit at an angle to each other. One or two faces usually run fine on a 3-axis mill with a vise flip. Three or more faces with a tolerance between them is where a turntable starts to pay for itself.

The second question is position tolerance between faces. If face A and face B must hold ±0.01 mm to each other, a manual flip adds stack-up from the vise, the parallels and the operator. A rotary table holds that relationship in one setup, so the error comes from the table index accuracy, not from re-clamping.

Write down the part envelope too. A 300 mm cube on a Ø400 mm table leaves room for clamps. A 600 mm part on the same table may need a riser block, and every millimeter of rise multiplies the load moment on the worm gear.

Do this on paper before you call a shop. It takes ten minutes and it stops the conversation from drifting into machine model numbers that do not matter yet.

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  Faces at an angleThree or more angled faces is the usual crossover point.
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  Position between facesBelow ±0.02 mm, one setup is easier to control.
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  Part envelopeLeave 50–80 mm per side for clamps and tool clearance.
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  Riser heightEvery 100 mm of rise adds load moment on the gear.

Catalog load ratings are static and measured at the table center. Real parts sit off center. A 100 kg rating measured at center can behave like 30 kg when the same mass hangs 300 mm out. Calculate the moment: mass in kilograms times distance in meters. A 40 kg part at 0.3 m gives 12 kg·m of tilt moment, and that is the number the brake and gear actually fight.

Cutting force adds to it. A 50 mm face mill in aluminium at 2 mm depth pulls a few hundred newtons, and that force acts at the part surface, not at the table center. High-feed roughing on an offset part is where rotary tables show their weak point: the brake slips, the index drifts, and the flatness reading moves by 0.02–0.05 mm across the face.

Index accuracy and repeatability are separate specs. Accuracy is how close the first index lands to the commanded angle. Repeatability is how close index 50 lands to index 1. For production, repeatability matters more. A table with ±15 arc-seconds repeatability holds a pattern across a full run; a table with ±15 arc-seconds accuracy but ±60 arc-seconds repeatability will not.

Backlash matters on reversing cuts. If the program indexes clockwise and then counterclockwise, any lash in the worm shows up as a step in the surface. Ask for the backlash figure in arc-seconds, not in degrees.

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  Moment, not massMass × offset distance is the load the table feels.
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  Repeatability first±15 arc-seconds repeatability beats ±5 accuracy for production.
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  BacklashAsk for arc-seconds, not a vague degrees figure.

Rotary tables use a worm gear, a roller cam, or a direct-drive torque motor. Worm gears handle high clamping torque and hold position when the brake engages, which suits heavy cuts and hard materials. The trade-off is wear over years and a small amount of backlash that needs adjustment.

Roller cam drives remove most backlash and index faster. They cost more and tolerate less shock load. Direct-drive motors remove the gear entirely, index in under a second, and hold sub-arc-second repeatability, but they need a brake for heavy cutting because the motor alone cannot resist a 50 mm face mill.

Thermal drift is the quiet one. The table body warms as the machine runs. On a 400 mm table, a 5 °C rise over four hours can move the part centerline by 0.01–0.02 mm. Shops that hold ±0.005 mm either run climate control, warm up the machine for 30–60 minutes, or measure and compensate.

For aluminium at high spindle speeds, direct drive plus a disc brake is a common choice. For steel and titanium with heavy radial cuts, a worm gear with a strong hydraulic brake is usually more stable.

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  Worm gearHigh clamping torque, needs backlash checks over time.
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  Roller camLow backlash, faster indexing, less shock tolerance.
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  Direct driveFastest and most repeatable, needs a brake for roughing.
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  Thermal drift5 °C body rise can shift centerline 0.01–0.02 mm.

A turntable adds setup time, programming time and inspection time. If the part is a simple plate with two holes and one face, a 3-axis machine with a vise flip is cheaper and faster. On a one-off part with loose tolerance, the extra fixturing rarely pays back.

Very large, thin parts are another bad fit. A 1,200 mm thin-walled panel may sag under its own weight on a rotary table, and the clamping force needed to hold it flat can distort it. In that case, a large 3-axis gantry or a vacuum fixture on a fixed table holds better geometry.

Parts that need turning and milling at the same time are a different story. That is mill-turn territory, not a bolt-on rotary table. A mill-turn center with a Ø400 mm table and a 4,000 mm bed handles shaft-type parts where a standard rotary table would need a long tool reach.

The honest test: if the part needs three or more setups on a 3-axis machine and the tolerance between faces is tighter than ±0.02 mm, a turntable usually wins. If it needs one or two setups, it usually does not.

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  Simple platesTwo holes and one face: stay on 3-axis.
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  Thin large panelsClamping distortion beats the indexing benefit.
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  Shaft-type partsMill-turn is the better fit than a bolted rotary table.

Ask how they verify the table. A shop that checks runout with a dial indicator and logs the result before each job is different from one that trusts the last calibration sticker. Ask for the index repeatability figure and how often it is re-checked.

Ask how the fixture is made. A rotary table is only as good as the plate bolted to it. If the fixture is machined in place on the table, the runout is controlled. If it was made on a different machine and bolted on, the error stacks.

Ask about the tolerance they will quote. A shop claiming ±0.005 mm on a 5-axis part should be able to explain how they measure it: CMM, roundness tester, or in-process probing. If the answer is vague, the number is marketing.

Finally, ask what happens when the table is the bottleneck. A 16-machine 5-axis shop can move a job to another table if one is booked. A single-table shop cannot. Capacity behind the machine matters as much as the table spec.

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  VerificationDial indicator log before each job, not just a calibration sticker.
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  Fixture originMachined in place on the table keeps runout controlled.
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  Measurement methodCMM or roundness tester, named, not implied.
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  Backup capacityMore tables in the shop means less schedule risk on your job.

We run 16 simultaneous 5-axis machining centers and 12 four-axis mills, with a Ø400 mm rotary table in the mix. That spread matters for CNC turntable selection: a job that needs fast indexing but not simultaneous motion goes on a 4-axis mill, and a job with complex contours goes on a 5-axis center. The table matches the part, not the other way around.

Tolerance on rotary work is held to ±0.005 mm where the geometry allows, with finishes from Ra 0.2–0.8 μm on fine work to Ra 1.6–3.2 μm as-machined. Every part gets raw material check, in-process monitoring and final inspection before shipment, with reports on request.

We work from one prototype to 10,000+ part runs with no minimum order quantity. Quotation and a free DFM analysis come back within 12 hours, and production can start within 24 hours of approval. Parts ship in 3–5 days on standard jobs, and uploads stay confidential with an NDA available on request.

If you are still comparing table types, send the drawing and the face map. We will tell you whether the job needs a rotary table at all, and which one.

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  16 five-axis centersSimultaneous motion for complex contours.
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  12 four-axis millsFast indexing for position-only work.
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  Ø400 mm rotary tableFits most fixture plates and mid-size parts.