Lathe 9x20 alignment problem

[zaebis]

Damn just noticed that on my 9x20 I have quite a runout on long parts. Anything that protrudes over 10" from the chuck I start taking off say 0.05" but finish 10" later cutting nothing. It is not wobbly part, I simply end up cutting no part. What may be wrong? How do I go about re-aligning it? I tried to fiddle with a tailstock but no luck so far. Are there standard checkup/alignment procedures?

[Al_The_Man]

There is normally a radial adjustment of the tail stock, you need a sacrificial bar and machine both ends and measure and adjust and recut until alighned.
Al.

[jhowelb]

Check to see that the bed isn't twisted (mounting problems) then set the tail stock center close up.

Set up your test bar on centers both ends and turn the piece with a "dog" and take a cut. If the tail stock end cuts a smaller o.d. (like it is doing now) then the tail stock end of the lathe could be tweaked high on the back side.

Try also facing off a good sized round close to the chuck. If it cuts concave then the head stock could be turned towards you. If it cuts convex it could be turned away from you. Most 9x20's have set screws where the head stock attaches to the ways.

Good luck!

[youngjim]

Correct me if I'm wrong, but:

If the chuck and the spindle axis are not straight, then the part will end up with a taper toward the tailstock.

If the chuck and the tailstock are aligned axially but not radially, then a cylinder cut will be out of round at either end, but equally.

So if the tool is cutting near the chuck, but not further down the part, does that not imply that the spindle axis and the ways are out alignment?

Like I said, if I've got it all wrong, I'd be grateful to know why.

Jim

[youngjim]

Looks like jhowelb answered most of my question while I was typing it.

Jim

[jhowelb]

Three things that I can see (there may be others) that can do this.
1. Tail stock misaligned.
2. Bed warped (ways twisted).
3. Head stock misaligned.

If you put a moris taper in the head stock then head stock misalignment is removed and you have only tail stock and ways to consider. If you have very carefully aligned the head to tail close to the chuck then you have mitigated the effect of tail alignment.

The sad fact is that these little machines were (mostly) produced in Hong Kong by slave peasants who do not understand nor do they care about precision.

Still, after taking the pains and headaches they make a pretty fair "hobby" quality lathe. Read about my tribulations on the subject here.

9x19 G4000 CNC Conversion

[DMF_TomB]

Dave Gingery's book how to make a lathe
and

http://books.google.com/books?id=TQ7...+hand+scraping

Machine tool reconditioning and applications of hand scraping
By Edward F. Connelly

I have seen most machines go out of alignment from
1) not made correct in the 1st place (rare but it happens)
2) lathe damaged from moving it.
3) lathe out of alignment because it is not level.
4) lathe alignment off because something moved when it was used. For example a Bridgeport turret knee mill head will go out of tram often if it is pushed or used hard enough. Something may need adjustment and bolt retightening.
5) bearing like in headstock worn, loose or some other problem
6) chuck mounting problem