Chatter on entry to finish pass of groove

[Nss88]

Hi all,
I have been having a bit of trouble trying to eliminate the chatter marks on the groove in the picture. the material is 303 stainless. machining strategy is using a roughing groove tool cutting down and stepping along (G75 on Haas lathe) leaving 0.25mm for the finish pass. the groove turn tool (Kennametal 4mm) side turns the finished size and it seems as it enters the bottom of the groove it chatters on entry then sorts itself out and the rest of the groove is fine? any suggestions would be greatly appreciated.
Thanks

 

[sinha]

Lack of clamping rigidity, resonance etc can be the cause of chatter.
Try reducing the RPM a little bit.
Does reversing the direction of finishing pass help?

 

[Nss88]

Hi, thanks for your reply, i have tried running in both directions for the finishing pass with the same results. I am currently running around 600rpm for the finish pass with a feed rate of 0.2 per rev. the chuck pressure is good and the bar is 28mm so I am thinking it should be rigid enough? I am machining as close to the chuck as possible. any other suggestions to try?
thanks

 

[Philabuster]

Hi all,
I have been having a bit of trouble trying to eliminate the chatter marks on the groove in the picture. the material is 303 stainless. machining strategy is using a roughing groove tool cutting down and stepping along (G75 on Haas lathe) leaving 0.25mm for the finish pass. the groove turn tool (Kennametal 4mm) side turns the finished size and it seems as it enters the bottom of the groove it chatters on entry then sorts itself out and the rest of the groove is fine? any suggestions would be greatly appreciated.
Thanks

The 4mm width of the groove tool is going to have a lot of tool pressure along with leaving .25mm for the finish pass. I would use a narrower tool width and reduce the finish stock allowance.

Is the Kennametal grooving insert a true flat bottom insert like a Top Notch or is it cupped a bit like the A4 style inserts? The cupped inserts work good for wide grooves because they have only 2 points of engagement at the corners vs touching the entire width of the insert.

 

[Milland]

You could try ramping to finish diameter starting from facing the outboard wall to .3mm of final D, then ramp for ~10mm to finish shaft diameter, complete the pass, then backturn to the outboard wall. If time is critical you could try making the ramp distance shorter (5mm), then backturn, then complete the rest of the D.

 

[Mr. Atoz]

Can you use a live center?