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How to Indicate a Part in a 4-Jaw Chuck
Guide · Updated October 28, 2026
A 4-jaw independent chuck lets you center a part as close as your indicator reads — often under 0.0002 in — and offset parts on purpose. It takes practice; this is the routine most machinists use.
Check your indicator
Verify your test indicator against known heights from the free Gage Block Calculator before chasing tenths.
Step by step
- Rough center: Use the chuck face rings to set all four jaws about equal, clamp the part lightly, and spin to check by eye.
- Mount the indicator: Put a dial or test indicator on the tool post or carriage, tip on the OD near the jaws, with light preload.
- Find high and low: Turn the chuck by hand (spindle in neutral) and note readings at each jaw.
- Adjust opposite jaws: At the high jaw, loosen the opposite jaw and tighten the high jaw to move the part half the difference.
- Repeat on the other pair: Do the same for the other two jaws, then go back and forth until the total reading is within tolerance.
- Check face and outboard: For long parts, also indicate near the end; for short parts, indicate the face to catch wobble and tap it in.
- Final snug: Tighten all jaws evenly a little at a time, checking the reading does not change.
Worked example
Readings at jaws 1 and 3: +0.006 and 0. Move the part 0.003 in toward jaw 3 by loosening jaw 3 and tightening jaw 1. Both now read about +0.003, meaning centered on that axis. Repeat on jaws 2 and 4.
Square stock
Indicate two adjacent flats. Rotate 180° and read the same flat: half the difference is the offset. Adjust as above.
Two-key trick
Use two chuck keys on opposite jaws so you loosen one and tighten the other in a single motion. It keeps clamping pressure steady and speeds things up.
Tips
- Read runout and TIR as the total swing, not one side.
- Keep the test tip parallel to minimize cosine error.
- Set tool height after the part is dialed in.
- For bores, see indicating a bore true.
FAQ
How do you center a part in a 4-jaw chuck?
Indicate the OD, find the high jaw, and move the part half the reading by loosening the opposite jaw and tightening the high one; repeat for both jaw pairs.
How close can you dial in a 4-jaw chuck?
With a good test indicator and patience, under 0.0002 in TIR is routine.
Why move only half the indicator reading?
The indicator shows total swing (TIR). The part is only off-center by half of that.
Should I use a dial or test indicator?
A test indicator is more sensitive and works in tight spots; a plunger dial indicator is fine for rough centering on the OD.
How do I stop the part from moving when I tighten?
Tighten jaws in small, even steps in opposite pairs and recheck the reading after the final snug.
Related guides and calculators
- Runout and TIR basics
- How to indicate a bore true
- How to set tool height on a lathe
- Turning speeds and feeds
- How to use a dial indicator
- Magnetic base indicator setup
- Cosine error with indicators
- Carbide insert basics for turning
- How to Face on a Lathe
- How to Use a Steady Rest
- How to Use a Faceplate on a Lathe
- How to Set Up Soft Jaws on a Lathe Chuck
- How to Use a Cathead on a Lathe
- How to True a 3-Jaw Chuck
- All free machinist calculators
- How to Align a Lathe Tailstock
- How to Use a Collet Chuck
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