Chatter - I am lost for ideas please help

Peeps.
Having massive issues with chatter on our lathe.
Machine is Daewoo 10hc with 1600 hours on it. 10inch chuck. Material is mild steel
I have to back turn a bearing bore. I have done hundreds of these parts and have had various degrees of success over the years.
The back turning op some batches runs great. 44.25mm bore. 1000rpm .12mm/rev dcmt insert finisher. 0.5mm depth of cut
Holds great size good tip life. Nowdays I may run 10 parts then chatter turns up. Real bad chatter. Tune it out by dropping to 400rpm and .22mm/rev but surface finish suffers. New tips don't help 25mm boring bar sticking out 95mm. Have just gone up to a 32mm bar same stick out but chatter even worse. Down to 200rpm to tune it out.
I have pulled all my hair out trying to get this right.
Next step is to recut the soft jaws. If that doesn't help then I will put the boring bar on another tool station. If that doesn't work then I will put the job on another machine and try it.

Anything I may have missed?

Carbide or heavy metal bore bar? What kind of bushing, split, slotted? Does your machine have variable spindle speed? If you have facebook, the group called "Machinist" with 112K members have a lot of manual guys who have extensive knowledge on ridding chatter.

Vibration was a killer for me i used moulding clay or Plasticine on the boring bar to prove my point ,I have a cheap lathe but locked up the top and cross slide a bit did some good .Also I believe steel aint what it used to be.

hello :) be sure that you are using the same insert as before

if you could use in the past "1000rpm .12mm/rev dcmt insert finisher. 0.5mm depth of cut", but now it does not work anymore, at least be sure that it is the same insert

it may be the material ... to be sure that it is not the material, you have to use same inserts as before, from the same insert lot, and compare axis loads, or, if possible, compare load diagrams

same insert may not be always crafted with same characteristics, thus is possible that a new lot of inserts is better/worse than a lot from 3 months ago

Quote:

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have had various degrees of success over the years

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maybe this is not ok; maybe it means that, so far, the setup was not stabilized ... as a consequence, it could go better or worse anytime, without a sign :)

all i can do, is recomand you kyocera dcmt 11t304mq ca6525 (r0.4), or 11t302mq (r0.2) / kindly :)

Determining the sources of chatter can be quite difficult. A few things that are often overlooked are tool tip height, how well the boring bar fits the adapter, how well the adapter fits the tool block, and condition of tool holder threads. For internal work, if the tool tip is only a couple of thousandths of an inch below center, the side of the tool can rub on the part. (If your machine has had even a very minor crash, the tool turret on a slant bed lathe may be misaligned enough to put tool tips above or below the spindle centerline.) Burrs on either the inside or outside of an adapter can reduce the rigidity of the setup enough to promote chatter since you end up with just a few points of support rather than a cylindrical fit for the boring bar. Rusty or damaged threads on tool holders can trick you into thinking you've secured a tool adequately, so be sure you can turn the set screws easily by hand, all the way to making contact with the boring bar.

post pictures and video with audio of your setup -
will be easier to get problem solved quickly