"birdsnest" when turning aluminum..

T

timbertoes

Active User
Registered
Joined
Apr 22, 2012
Messages
62
what a mess..
what am I missing to keep from having a birdsnest of aluminum swarf...ie have the chips shorter and break on thier own.

had this when:

taking .03 to .05 deep cut. running about 900 or so rpm. stock was being reduced from 1.75 to 1.5 " dia.

tried different feed rates (not slow though) kind iof a medium rate. sorry at work, can't look to see what it was.
Used both a HSS and carbide bit.
 
Some of it depends on the alloy. Aluminum, like most metals, is more ductile when hot, as it is when sheared off during the cut. This makes it hard to get a chip to break. That relies on the chip to be cooled and brittle. Lots of variables there. Normally, people use a high positive top rake for aluminum, and that has it's advantages. But one disadvantage is that is is near impossible to get a chip to break. If you find the right insert, specified for aluminum alloys, you should be able to get a broken chip. It usually takes a fairly aggressive feedrate, along with a high surface speed.
 
Some inserts also have a chip breaker slot milled behind the edge to cause the chip to curl beyond it's tensile limit and break. It's that little line that goes all the way around the triangle shaped bits. If you are not using indexable bits, you can file a chip breaker into the top of you Hss bits and it may help. Have a look at Mt Pete22 you tube presentation on bit grinding and you will see where to place it. Hope this helps

Bob
 
Afraid you're going to have to grind that chipbreaker. Never get a file to cut HSS. Easy enough to grind if you have a sharp corner on your wheel. The groove should be shallow, about .020-.030, and close enough to the edge to almost form the rake angle. The corner of the wheel will plow a 90° groove in the top of the tool, and even after you have that, adjusting the top rake can be easy, because the only material affected is the narrow area between the chipbreaker groove and the actual cutting edge. The object is to force the chip to hit the back of the groove and curl up tight enough to break rather than just bend into a curl and still birdnest.
 
Timbertoes,
I don't have an answer, but I have a story.

I have been working on this big project that involves a LOT of profile facing work on a bunch of 4.5" OD aluminum parts (6061).
I too was getting bird nests. The worst of it was they would build up between the toolpost and the work and block my view of the cutter.
I also tried various speeds, feeds, lubricants and tools. I finally found one insert that made long "springs" instead of bird nests. As I faced along, this long tightly wound "spring" would find its way off the back of the lathe, twisting and glimmering as it went to the floor. These things eventually break and restart, but there were 3' and 4' long springs all over the chip tray and the floor. I don't mind the springs so much, because it keeps my line of vision open to the cutter - and they fall off the back of the lathe where I can deal with them the next day (or the day after that).

Along comes my wife. She sees these things all over the floor (they are shiny and cute after all). She picks one up, examines this wiggly thing and wonders out loud if they could be made into a bracelet or something. I didn't say a word - I just show her the palms of my hands that were black from handling the aluminum stock. She drops the swarf as if it were radioactive, and walks out. If I had to make these springs for a living, they would probably refuse to form.

Terry S.

edited to correct spelling
 
I would like to see pictures of the tool you are using. Especially the HSS one. I want to see your grind. It sounds like a profile problem. Wrong top rake, not enough clearance etc.

"Billy G"
 
I also got a terrible birds nest when I used a braised carbide bit, I changed to high speed steel sharpened with Mr. Pete's recommendations, I got a much smoother cut and chips instead of Curls.:tiphat:
 
thanks, lots of good info, and even radioactive Al :)

The HSS bit was an A. Warner HSS insert tool

the carbide was a Grizzly 'whole buncha bits for not a lot oof money" kit. :)

I ordered some carbide bits from A. Warner today. I know of the little groove...I guess know I know what it does :)
I have some...but a lathe crash a while back, took out my only insert screw for that tool. One I got at a local surplus place.

I did read that some people will cut from the chuck - outwards. to keep the birdsnest from wrapping on the chuck.
 
A trick I use when AL is to soft to break up the chip is the shop vac. Held close to the tool. It sucks the string as it cuts.
 
You must log in or register to reply here.
Back
Top