Boring 6061 - horrible surface finish!

I am attempting to bore 65mm holes in 4" aluminum bar. A photo of the result is attached. It's ugly! I have experimented with alot of variables but still get this tearing of the metal instead of a clean cut.

Machine: Tormach PCNC 1100 series 3
Controller: PathPilot
Tool: 1/2" Glanze through-coolant boring bar (steel)
Insert: CCMT, tried one for steel and one for aluminum with the same result
Surface speed: 150-500 meters/min
Feed rate: 550-800 mm/min
depth of cut: 0.25-0.5mm
Insert is parallel to X-axis and centered in the bore

All the other cuts on the machine are working great. Facing, turning, parting are all no problem. What am I doing wrong with boring?

That's fairly aggressive I would think. Looks like it chattered a lot.

Are you using the shortest boring bar possible? Just long enough to reach bottom of bore.

Quote:

---

Originally Posted by vertcnc

Are you using the shortest boring bar possible? Just long enough to reach bottom of bore.

---

The hole is only 3/4" deep, The boring bar stickout is about 1.25" right now. If I eliminate the through-coolant, I could choke is up right next to 3/4".

On my manual lathe, I can run a lot more stickout than that with no chatter. And that's with a cheaper, thinner boring bar.

Try again at 3-500 rpm 50-80mm per minute. I've not used the tormach but when I'm having trouble boring that range almost always works well.

Ben

Thanks for all the help and suggestions here. I finally fixed the problem by a combination of choking up on the boring bar as far as possible, re-routing the coolant line to maintain through-coolant, .25mm depth of cut, 157 m/min surface speed, and 550 mm/min feed rate.