Professionals and Amateurs Together

Lathe Runout


How do I make sure a lathe is running true (round)? – Bob St. Laurent


Brooks Tanner replies: Measuring lathe runout is a relatively simple procedure. Tools needed are a dial test indicator and a magnetic base, or other base to hold the indicator. A base and indicator set which will work well for this application is often on sale at MSC for $25.

To make the measurement, attach the base to one of the lathe weighs and place the tip of the indicator perpendicular to the inside wall of the morse taper. Rotate the lathe by hand and watch the indicator needle. Stop the rotation at the lowest reading and set the dial to “0”. Now rotate the lathe until the needle reads its highest. This reading is your runout. Repeat this test on the outside of the shaft. The taper should be concentric with the same runout to the outside of the shaft but is not guaranteed. Similar procedures may also be used in measuring runout of other tools such as your table saw, drill press and chop saw.

Joe Barry replies: To check the truth of a lathe, grasp and try to move the spindle to check the bearing play. Then put a point center in both the headstock and tailstock and slide the tailstock up so they are tip to tip. Adjust the tailstock if they don’t line up.

If you have a patternmaker’s or machinist’s lathe, you can use a test bar (a known straight round bar with centers at each end) between the centers. Slowly feed from the headstock to the tailstock using a dial indicator. Watch for any deviation.

For those of us with a regular wood lathe, use the dial indicator secured to the bed with either a magnetic base or a clamp. Check the spindle for run-out using the dial indicator while rotating the spindle by hand. You can then check your various chucks for run-out also.

Geoff Ames replies: Before running your lathe, insert a spur pointed drive center in the headstock and a spur pointed center in the tailstock. Loosen the tailstock and move it to the headstock. The two centers should touch point to point.

Sharpen your gouge. Then set up your lathe and turn a spindle round with no chatter. You can then run a pencil in the center of the spindle and observe if the spindle is marked evenly around the full circumference of the spindle.
If you turn a long s

indle, you may experience some wobble at the center. This is normal and usually requires a hand behind the turning or a steady rest.

If you are scraping rather than cutting, you will experience rough going and will need to sharpen your tools far too often. Often what seems to be a poorly running lathe is a turner who needs a little practice or a lesson.

Jon Siegel replies: All lathes run true if the axis stays in one place. Maybe the centers are poorly manufactured and don’t run true (replace or re-machine them). Maybe the bore doesn’t run true, or the threads don’t run true, but you can’t fix these things. And they don’t have anything to do with turning a workpiece round.

Tags: Lathe, Woodturning