9x20 Sudden Chatter

[Duder321]

Very discouraged. Hopefully someone can offer some ideas that lead to a solution.

Long story short: Moved from TX to IN last April. The lathe was the last thing to get setup and put back into service. It was moved (as far as I saw) still attached to its stand using a hand truck from the backside and two guys holding/guiding it. Prior to the move the machine was working fine - good as expected for a 9x20. I typically used a solid plinth under my QCTP for turning and made a donut mount for the compound when I need it. All was well like this for several years of use.

Fast forward to now, lathe is setup, leveled, etc. Cross slide gibs and handwheel seem to feel the same as before. Same tool setup as described using sharp HSS tool that previously worked fine - Chatter city. Just awful. No matter the RPM, diameter, Aluminum, Steel. 5, 10, 20, 40 thou DOC - Doesn't matter. I ground up a new tool and carefully honed it razor sharp. Even leaves a rough chattery finish in aluminum.

I can stop the howling with a really aggressive feed rate and moderate DOC or by using a live center but the surface finish still has a chatter marks.

Help! What to check and how to check it. Thanks.

[John Evans]

How solid is the floor ? Check HS to bed bolts ,HS may be moving a bit. Finally spindle loose? Can't see the last just from shipping though. Odd thought check drive belt[s] for set/damage.

[ccfl]

Does it chatter on both facing & turning cuts? I had horrible chatter problems that turned (ha, pun!) out to be not enough spindle bearing preload, but it only showed up while facing. When turning you'd never know there was anything wrong. The common test for checking deflection with an indicator on the chuck OD/backplate while pushing/pulling on a bar clamped in the chuck said everything was A-OK. It clearly was not A-OK since cranking in a fair amount of preload fixed it.

[JackF]

Something to think about. Could there have been a mishap in moving while you were not observing? If by chance there was I would look for a crack in anything associated with tool holding, cross slide, head stock or etc. Just a thought.



Jack.

[Bill C]

I've had similar issues in the past. Tracked mine down to lack of lubrication to the steel shaft the driven pulley rides on (that was an 8 x 14, not sure if the 9 x 20 is the same design). Suggest unplugging, removing drive belt, then going one by one from motor, to pulley, to pulley, to headstock, turning by hand to see if there is any stiff part. If not, try motor first with no load, then replace one belt at a time. You just have to "play detective" - isolate the one part causing the issue.

Good luck,

Bill

[John Hasler]

> I can stop the howling ... by using a live center

I think that's significant. If it was anything on the carriage I don't see how a live center would help.

[Harold_V]

I can stop the howling with a really aggressive feed rate and moderate DOC or by using a live center but the surface finish still has a chatter marks.

I would certainly consider the preload of the headstock bearings.

Harold

[SteveHGraham]

Tighten everything.

[Duder321]

Thanks to everyone for the ideas. I finally got a little time to go and work through some things. I think it was a combination of items.

• Not stable enough. I think my new garage slopes just little bit more and how I had the stand shimmed level wasn't allowing enough contact. It didn't seem to rock any more when you push it around, but when running, I could feel the headstock bouncing.
• Drive belt tension. The cogged belt that goes from the motor to the drive pulley was too loose. I'm thinking maybe one of the movers used the motor as a handle to heave it in place or lift it causing the motor to shift and belt to become slack.
• Bearing preload. There's a method described in the 9x20 rebuild for setting the preload. I was a little loose based on that method. I snugged things up and measured the temps after a good run. The spindle now has a good bit more drag, but never runs hot.

That seemed to help a lot. I was able to take some cuts in steel and stainless without a disastrous result as before.

Damnit! I thought I had a good excuse to go shopping for a new lathe

[liveaboard]

Something I remembered today;
I once had a chip [or two] get under my carriage. All sorts of bad things happened [including chatter] before I took it off for a full clean.