how do you measure runout on a lathe?

[Dean Matthews]

I have seen a couple of posts commenting on runout but I am not exactly sure how to measure it.

How would I check it on my talon chuck?

[TYLER WOOD]

Bump Bump Bump

[Bill Stevener]

Hi Dean,
Most of the time one will use a dial indicator to check the run-out on a chuck, or what ever.
If you are lacking the same, you can try this. Move your tool rest to within .025" of the chuck at it's center point.
Using a straight edge, such as a 6" scale, place it on the tool rest and against the chuck. Rotate the chuck, observe the movement of the straight edge and note any gap between the chuck and straight edge. When you are sure of the largest gap, check it with a feeler gauge. This will be your run-out.

Got it, simple??? OK.

[John Hart]

Kinda what Bill says....cept I'll measure with dial calipers instead of feeler guages. Both work.

[Dean Matthews]

hmm...

I actually took a sqaure and put it against the lathe bed and then had the vertical portion rest against the face of the chuck. I placed the straight edge up against the metal and moved back just a hair. Then put a light behind it and spun the chuck.

Visibly there is no change in the gap. i would think that if I cannot see anything it can't be that bad. Right?

[John Hart]

Visibly there is no change in the gap. i would think that if I cannot see anything it can't be that bad. Right?

That's what I would think.....You might want to check it along the axis as well, by placing your square against the outer diameter of the chuck and look for runout that way. Something might show up axially that doesn't show up radially....not very often...but it happens.

[Jim Becker]

You can check it visually by putting a drive center in the headstock and a live center in the tailstock and then bringing them to where they nearly touch. The points should line up with the machine off. Turn on the machine at a low RPM and watch the two points. They should stay aligned visually as the lathe spins. If you see a wobble, reset the taper and try again. If it continues, you have "measurable runout".

The way to quantitatively measure it is to clamp a dial indicator to a tool rest or other fixed position so that it rides on the spindle. (or faceplate/chuck if you want to check that, too)

[Bill Stevener]

Sorry I didn't note the side of the chuck, as close to the face as you can, I guess I thought this was a given. As John noted, a dial caliper works well, if you have one.
.005" may be OK. The average human hair is .002" as a guide.
Remember, in some cases, the further away from the chuck, the work is, the grater the spiral.

[Curt Fuller]

One other note, checking the runout with your chuck screwed onto the spindle may just indicate that the chuck was not threaded perfectly or the threaded insert isn't set correctly. If you have runout on the chuck, take it off and also check the lathe spindle to see of the runout is also in the spindle.