How do I prevent stringers when cutting aluminum on the lathe?

[ibuildstuff4u]

Hey guys, I have been cutting a lot of 6061 aluminum on the lathe lately and have been having trouble with long stringers that wrap around the chuck dangerously and want to know if there is any way to prevent this.  I tried changing the spindle speed as well as the cutting angle of the insert and still have this problem.  I'm using some good inserts that are made for aluminum and are suppose to help break up the chips but they don't seem to work.  Here are the inserts that I'm using http://www.grizzly.com/products/Carbide-Inserts-TNMG-for-Aluminum-pk-of-10/H8330  and I'm running the spindle at 620 RPM but I also have tried 1100 RPM with out any change.

Thanks for the help! Dale P.

[bigmini]

The simple way I've found to achieve this is to interrupt the feed every so often. That may leave a slight ring at each stop, but you can run a continuous finishing cut to get rid if those, and the swarf is so fine then it is less of a problem.

Another way is theoretically to grind a chip breaker into the tool. This is a groove just behind the cutting edge that forces the chip through such a tight radius that it breaks off. Not sure if it makes any difference with aluminium. Some carbide inserts I've seen have this built in, but I haven't  used them in years and never on aluminium.

[ibuildstuff4u]

The parts I'm making are only 3.5 inches long and even with interrupting the cut I still get long enough stringers that they can wrap around the part and make a mess.  Here is a picture of the inserts that I'm using to show the chip breaking profile that they have but they don't seem to work.  I tried using some inserts made for cast iron and steel and I get the same results.

[Jonny]

Pretty confident they are not proper inserts for working aluminium just general purpose.
An uncoated, tips with radius work best but do have tendency to like Iscar, Ceratizit and certain Kennametal tools and tips.

Chip breaker will only work with certain aluminium grades that are brittle or free machining.

As above keep backing off, it will break up the stringer. Final pass for a finish.
If you intend to remove metal like 5" plus diameter with a recess going in 1/2" i usually do tis in two maybe three passes. If you get the feel for whats going on you can get the continuous string to wrap around itself and bunch up.

Taken on previous lathe about 12 yr ago an action shot at 1000rpm 5" dia aluminium blank in small chuck, one pass on power feed facing off 1/2", no wrap around just a bit of swarf in tray at back. http://pic20.picturetrail.com/VOL15/728921/1252422/14582043.jpg
Its very rare it ever wraps around the chuck perhaps 1 in 70 jobs, just make sure the swarf dont knock tools off head stock. Verniers gone a few times.

[ibuildstuff4u]

I bought these inserts from Grizzly and I was told they were made for aluminum, but your may be right about being general purpose as they work just fine on steel and cast iron. 

Thanks for the help, Dale P.

[Jonny]

Purely on past experience what is meant for cast iron is usually pretty good on aluminiums.
Most aluminium tips have a radius.

Apart from using a free cutting aluminium grade which will come off in smallish chips, i dont think you have any choice except to keep backing off.
I changed a tip over today from a different make meant as a pure H13 tip to another make with a deep recess behind the cutting edge and larger rad. There are no chips now, massive unbreakable thick stringers after a few seconds, that wont disperse in to tray. A couple more secs and catches previous stringer wrapped around tool and tool post then wraps around job all within 6 secs. These tips were meant for free cutting aluminium.
What i would suggest is try a decent brand tip uncoated with minimal relief behind cutting edge. Its easier to break the chips up. If you look and watch you will see fine cracks as its cutting.

I do use a bullnose carbide tool for recessing a certain job with a lot of rake for clearance, chips are continuous and quite large
but easy to break up.

[Mayhem]

Did those inserts come with an indication on the depth of cut (ap) and feed rate (f) that the chipbreaker on is designed for?  Good quality inserts will either have this information on the package or available in their product catalogue.

I suspect that you may not be feeding them into the work enough for the chipbreaker to actually work.  Try a different combination of feeds and depth of cut.