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How to Use a Cathead on a Lathe
Guide · Updated October 28, 2026
A cathead is a sleeve with two rings of adjusting screws. It clamps onto rough, square or finished stock and gives the steady rest a true, round surface to run on, so the steady jaws never touch the part itself.
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Step by step
- Slide the cathead on: Put it over the work near the end that needs support.
- Snug the screws: Lightly tighten both rings of screws so the work sits roughly centered.
- Indicate the work: With an indicator on the work near each ring, adjust opposite screws until it runs true.
- Indicate the cathead: Check that the cathead OD runs true; it must, if it was turned true on its own.
- Set the steady rest: Close the steady jaws onto the cathead OD, not the work.
- Lubricate: Oil the cathead track or use bearing-tipped jaws.
- Machine: Face, center drill or bore the end of the work.
Worked example: indicating out runout
The indicator shows 0.006 in TIR near the outer ring. The work is off center by half the TIR, 0.003 in. Back off the screw on the high side 0.003 in worth and tighten the opposite one, then re-read. Repeat at the inner ring. Aim for under 0.0005 in TIR at both rings before closing the steady rest.
When to use a cathead
The work is square, hex or rough and cannot run in a steady rest. The finished surface must not be marked by steady jaws. The work is crooked and needs to be aligned to one part of it.
Making a cathead
Turn a steel tube true inside and out, then drill and tap two rings of 4 screws each, 90° apart. Bronze or brass tipped screws protect finished work.
Common problems
Work walks out of true: screws not tight or work not supported at the chuck end. Galled cathead OD: no lube. Chatter: steady jaws too loose.
Tips
- Steady: steady rest setup.
- 4-jaw: indicating in a 4-jaw uses the same half-TIR rule.
- Indicator: dial test indicator.
FAQ
What is a cathead?
A sleeve with adjusting screws that gives a steady rest a true surface on rough or odd stock.
Do steady jaws touch the work?
No, they run on the cathead.
How many screws?
Usually two rings of four.
How do I true it?
Indicate the work and adjust by half the TIR.
Why use one on finished work?
To avoid marking the finish with steady jaws.
Related guides and calculators
- How to Use a Steady Rest
- How to Indicate a Part in a 4-Jaw Chuck
- How to Use a Dial Test Indicator
- How to Face on a Lathe
- How to Center Drill and Spot Drill
- How to Machine Hardened Steel
- How to Cut a Taper with a Taper Attachment
- All free machinist calculators
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