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How to Use a Bench Center
Guide · Updated October 27, 2026
A bench center holds a part between two centers so it can be turned and indicated. It's the standard way to check runout on shafts, arbors and turned parts against their center holes.
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Step by step
- Check the centers: Clean the centers and center holes, and check the center points for damage.
- Mount: Mount the part with light tailstock pressure. It should turn freely with no end play.
- Set the indicator: Mount the indicator on the base, square to the diameter.
- Rotate: Turn the part one revolution and read the TIR at several positions.
- Compare diameters: Compare each diameter's runout to check concentricity to the centers.
Tips
- Too much center pressure bends long, thin parts.
- Use test bars to check the bench center itself.
- See runout and TIR basics.
Related: runout and TIR, checking V-blocks.
Worked example: checking runout on a ground shaft
Mount a 1 in diameter shaft between the centers with light, even pressure: snug enough that there is no end play, loose enough that it turns freely by hand. Put a 0.0001 in test indicator on the shaft at three positions along its length and rotate it slowly. Readings of 0.0002, 0.0003 and 0.0002 in TIR mean the shaft is within a 0.0005 in total runout callout.
Check the centers first by running a master test bar between them; any runout on a known-good bar comes from the centers, not the part. Dirt in a center hole can add several tenths, so wipe the center holes and points before every check. To separate bend from out-of-roundness, compare runout at the ends to runout in the middle; a bent shaft shows the largest reading in the middle with the high spot at the same angle at each position.
Write down readings and the angle of the high spot with a marker on the part. That record makes straightening or deciding to regrind much easier.
Fuller worked example: runout to eccentricity
A shaft between bench centers shows 0.0010 in total indicator reading on a journal. The eccentricity of that journal relative to the center holes is half the TIR, 0.0005 in. If a second journal reads 0.0002 in TIR with the high point 180° away, the two diameters are not coaxial and straightening alone will not fix it.
Clean the center holes and check the centers themselves with an indicator first; dirt in a center hole can show 0.0003 in or more of false runout.
FAQ
What is a bench center?
A base with two centers that holds a part for indicating runout.
How much pressure?
Just enough to remove end play while the part turns freely.
Bench center vs V-blocks?
A bench center references the center holes. V-blocks reference the diameter.
How do I verify the indicator?
On gage blocks. Build any reference size free with the Gage Block Calculator at gageblockcalc.com.
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General shop information only — follow your gage manufacturer's instructions and your quality system.