how to fix out of round/runoff/wooble???

[fpm]

Hello guys.
This is my second thread,and I could not find anything when doing a search.
I have the Harbor Freight 7x10 mini lathe. I am doing my own spacers for a project.
Yesterday I purchased 1.5 inch diameter 6061 , two 6 inch pieces. I set it in the chuck and it was out of round/wobbling.
I checked the flatness of the end face where it was cut. Seems straight.
I attempted to correct it by tapping it while spinning at a super low speed. But there is still a slight wobble but much better than before.
I cut the aluminum down to a 1.5 inch long piece. MUCH easier to work with,but that a faint wobble. I was able to face it to further take out the wobble and put that side into the chuck-much better again!
I will be purchasing a digital gauge to know how out of round the part actually is.
My question is how do you correct this while in the chuck? Is the 1.5 diameter too big for the 3 inch chuck?
Those little teeth seem pretty small to relly hold onto something large.
Also, what is an acceptable "out of round"?
Thanks,
-Frank

[MechanoMan]

The runout gauge is the only way to go. You cannot get decent accuracy by feel alone. Harbor Freight sells a nice digital one, AND a magnetic stand with any-way-you-wanna-go adjustable arms.

Self-centering chucks ALWAYS have runout limitations, the Sherline's supposed to be 4 thou. An independent chuck can have runout reduced to any degree the user cares to fiddle it to. In 60 sec an operator can reduce the runout on a 4-jaw indy much below what a self-centering can do, 1 thou is easy. At that point any runout is actually in the irregularity of the round stock's surface not the chuck itself. BTW, 4-jaw indy is much easier to adjust than 3-jaw indy and the holding force is better. Plus, it can hold square and round stock equally well.

The runout at the chuck and the runout at the end of the stock are two different issues. The first you fix by adjusting an indy chuck. The second you fix by semi-loosening the chuck and tapping the stock back and forth and making sure it's not being worked out of the chuck in the process, and retighting/recentering it in the chuck if need be.

There is no fixed number for acceptable runout. This depends on your situation and what you actually need.

A side lathing operation can have runout and still cut vibration-free IF the cutting rate is high enough to make a continuous, coiling swarf. If the swarf is discontinuous, it'll vibrate as it chips off, regardless of runout. This is not always a problem though, just undesirable.

[fpm]

I purchased a digital read out gauge. What a difference. I was able to adjust the run off to 0.001 inches!!! Huge difference.
Thanks.
-Frank

[Twmaster]

The chuck that come on the H-F 7x10 machine has a factory tolerance of .003" worth of runout.

You can do a couple things to check your machine. First take the chuck off and use your new indicator to check the runout of the spindle flange. If waaaay out you may want to make a light facing cut on that.

One thing to remember. Anything that you have sticking out more then 3 or 4 times it's diameter from the chuck should be supported at the far end either by a center in the tail stock or a steady rest.

[Dougal]

As chucks wear, they often get bellmouthed. The tips near your cutter end up worn/damaged and don't grip the part, instead the jaws only make contact further in.
This results in a part that will be close to concentric near the jaws, but further out as you get further from the chuck. I think my 3 jaw is getting close to this point.

You can fix that by honing it, I've done it before using a piece of cast-iron, a drill press and grinding paste. But there must be many methods.