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How to Use a Tool Post Grinder
Guide · Updated October 28, 2026
A tool post grinder mounts on the lathe cross slide and grinds hardened shafts, bores and centers true in the lathe. The work turns slowly while the wheel spins fast in the opposite direction at the contact point. Abrasive grit is the enemy of the lathe, so protect the ways before you start.
Size to tenths with blocks
Grinding works in tenths. Confirm your mic or bore gage on gage blocks at the target size. The free Gage Block Calculator builds the stack.
Step by step
- Protect the lathe: Cover the ways, leadscrew and chuck area with plastic or cloth; set a magnet or shop vac near the work.
- Mount on center: Set the wheel spindle on the work centerline so the wheel meets the work at center height.
- Check wheel speed: Never exceed the wheel max RPM; typical surface speed is 5,500–6,500 SFM.
- Set work speed: Run the work slowly, around 50–100 SFM, so the surfaces pass in opposite directions at contact.
- Dress the wheel: Dress in place with a diamond so the wheel is true to its own spindle.
- Light infeed: 0.0005–0.001 in per pass, 0.0001–0.0002 in for finishing, traverse with power feed.
- Spark out and measure: Take passes with no infeed until sparks stop, then measure.
Worked example
A 4 in wheel at 6,000 SFM: RPM = 3.82 × 6,000 ÷ 4 = 5,730 RPM; check the wheel is rated above that. A 1.250 in hardened shaft at 75 SFM: RPM = 3.82 × 75 ÷ 1.250 = 229 RPM. Traverse about 1/3 of the wheel width per work revolution: a 0.5 in wide wheel, 0.17 in per rev × 229 = 39 in/min. Grinding from 1.2510 to 1.2500 in at 0.0002 in diameter per pass (0.0001 in on the dial) takes about 5 passes plus spark-out.
Infeed on diameter
Remember the cross slide on many lathes reads diameter or radius. A 0.0005 in radius infeed removes 0.001 in from the diameter.
Common problems
Chatter marks mean the wheel is loaded, out of balance or not dressed. Taper means the compound or carriage path is not parallel to the axis. Burns mean too much infeed or a glazed wheel.
Tips
- Dress: dress a grinding wheel.
- Speeds: grinding speeds and feeds.
- Runout: runout and TIR basics.
FAQ
Does grinding grit damage a lathe?
Yes if it reaches the ways; cover the ways and clean up thoroughly.
Which direction should the work turn?
Opposite to the wheel at the contact point.
How much do I take per pass?
About 0.0005–0.001 in roughing, 0.0001–0.0002 in finishing.
Can I grind bores?
Yes with an internal quill and a small wheel.
Why must I ring-test the wheel?
A cracked wheel can burst; ring test before mounting and never overspeed.
Related guides and calculators
- How to Use a Surface Grinder
- How to Dress a Grinding Wheel
- Grinding Speeds and Feeds
- Runout and TIR Basics
- How to Indicate a Bore True
- How to Cut Square Threads on a Lathe
- How to Use a Quick Change Tool Post
- How to Balance a Grinding Wheel
- How to Machine Hardened Steel
- How to True a 3-Jaw Chuck
- All free machinist calculators
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General shop information only — follow your machine and tooling manufacturer's instructions and your shop's safety rules.