Is .0005 runout in 10" acceptable?

[marfaguy]

I decided to see what the run out on the new lathe is using the Rollie's Dad's method.
http://www.neme-s.org/Rollie's_Dad's_Method.pdf
I got the new Lathe setup and leveled in. I've got a piece of .750 Drill rod that's pretty straight and is a very consistent .750 throughout.
I mounted it in the 3 Jaw and used it to test with. At the chuck, about .250" from the jaws the total difference in a full revolution was .001". So the near end average is .0005. Then at the other end ( almost exactly 10") the total amount was .002" so the far end average is .001" The difference between near end average and far end average is
.001 - .0005 = .0005.
So If I understand this correctly the runout is .0005" in 10", correct?
Thats seems pretty good to me but I don't really know. Should I try and correct that out or just leave it alone?

[doubleboost]

(06-30-2013, 04:50 PM)marfaguy Wrote: I decided to see what the run out on the new lathe is using the Rollie's Dad's method.
http://www.neme-s.org/Rollie's_Dad's_Method.pdf
I got the new Lathe setup and leveled in. I've got a piece of .750 Drill rod that's pretty straight and is a very consistent .750 throughout.
I mounted it in the 3 Jaw and used it to test with. At the chuck, about .250" from the jaws the total difference in a full revolution was .001". So the near end average is .0005. Then at the other end ( almost exactly 10") the total amount was .002" so the far end average is .001" The difference between near end average and far end average is
.001 - .0005 = .0005.
So If I understand this correctly the runout is .0005" in 10", correct?
Thats seems pretty good to me but I don't really know. Should I try and correct that out or just leave it alone?

I would leave well alone
John

[EdK]

Rollie's Dad's method is only useful after you've taken any twist out of the lathe bed. As John said, unless there's an obvious problem I'd leave it as is and just use it for awhile.

Ed

[marfaguy]

Thanks John and Ed. Just to be clear leveling is what's supposed to take twist out of the ways, right? Also, I can't quite get the ways exactly level with the machinist level. The best I can do is get it to the point where the bubble is pretty close but if I put I cigarette paper (.001") under the low side the bubble jumps to being "more out" the other way.
As it stands right now it's about 3 ticks out from left to right and about 2 ticks out front to back at the chuck end,
about 7 ticks out in the middle and about 4 ticks out at the far (tail stock) end. All of the front/back measurements are out in the same direction.

I'm using brass shim sheets of varying thicknesses to make shims out of. Those should be fine I would think.

[TomG]

Rollies dad got it right and his method is all you need to take the twist out of the bed, the level is not even required. It is essentially mapping the centerline of the spindle and by shimming the feet on the lathe, making that centerline parallel with the ways both horizontally and vertically. Getting back to the original question though, if you followed the procedure and got .0005", that is more than acceptable. I'd say you are finished.

Tom

[Sunset Machine]

.750 sticking out 10".. Well, .0005 is a great figure but you tested the chuck against an unknown and possibly got a meaningless result. A proper test means making chips.

You should make some chips from a 1" diameter bar (half of maximum length) mounted between centers (don't use the chuck). Then do a long one (full length) between centers and compare results. That will test bed and tailstock alignment.

You should try the short one with the tailstock quill both extended and retracted (re-locate the tailstock), running an indicator along the top and sides of the work. This will test quill alignment.

Finally, turn a bar about 4 inches long mounted in the chuck alone (don't use the tailstock). That will test headstock alignment. See if the work is actually round. That will test the spindle bearings.

You can use a few collars glued to the bars to save material and time, and as a bonus taking tool wear out of the picture. Not important, but the bars would best be hollow with a thick wall, and RPM should be kept low to minimize things from winging about from being out of balance. Nitpicking a bit..

Btw, the Rollie test doesn't take sag into consideration but it takes a lot of sag to influence the result. You don't need a level to "level" a lathe, the Rollie test works fine. A level is faster/easier.

[PixMan]

Rollie's dad's method is excellent, but I have a highly biased because Rollie is a friend and neighbor of mine.

[TomG]

I like it because it doesn't require a precision test bar and it takes the quality and condition of the chuck out of the equation.

Tom

[EdK]

I still question how useful it is on a lathe with a bed that has not been checked for no twist and the twist removed if present.

Ed

[Sunset Machine]

It creates an imaginary line that you test the bed against. Rollie's method on old lathes can be confusing, because of headstock/spindle problems pointing that imaginary line at your right knee, but it does well in taking the twist out of a bed.

Btw, I misread the first post thinking marfaguy was simply checking runnout. Guess I didn't get past the title, sheesh.