Running bore bar

[Kuzel]

So I'm running a tube of A519. OD of 5.500 and ID of 3.00
I am having issues with humming and chatter when boring. Boring from 3.00 to 3.480 and 7inch deep. Steel bore bar with negative rake insert cnmg432-tf ic8250.
Its currently set to run at DOC .120, 200sf and .010ipr. It hums loud and may chatter at times.
I've had it set to run at DOC .060, 470-520sf and .010-.012ipr. It came out with a shine and made no noise while cutting but didn't last long before serious chatter all the time and broke inserts like crazy.
Thoughts?

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[fc60]

Greetings,

We used to machine hollow tubes.

To curtail the vibration, we would wrap a piece of surgical tubing around the part to dampen the harmonics.

Cheers,

Dave

[Algirdas]

It doesn't look "long" enough to chatter. Check ir your cutting point is not above the rotation axis.

[OldSchoolProgrammer]

As thick walled as the material is, the boring bar setup is the most likely culprit. Use the largest diameter bar your machine and the part can accommodate, use minimum hang-out of the bar, use the smallest radius insert which can tolerate the operating conditions, and play around with reducing cutting speed and increasing feed rate. If doing all of those things doesn't help, consider using a bar and insert with a zero or slightly positive rake. If you're trying to make a profit and are running lots of those parts, consider a carbide boring bar. It has a much higher resonant frequency.

[deadlykitten]

steady rest + harmonic function