Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: guynamedbathgate on August 29, 2008, 03:38:19 PM

Title: chip control on cnc lathe
Post by: guynamedbathgate on August 29, 2008, 03:38:19 PM
For those of you who are running cnc lathes I have a question.
I am having a terrible time managing my aluminum chips. I am running a long program and I am getting these 3 foot long coils instead of nice neat chips from the operation. the chip breaking indexible insert Im using doesnt work worth a damn and sitting there pulling the chips as they unspool from the part defeats the whole purpose of a cnc. What is everyone else doing. Machining stainless is more fun than trying to snatch aluminum turnings out of a machine before they end up wrapped around the chuck without getting your fingers sucked in. No fun at all.
I look forward to some suggestions.
CB :-\
Title: Re: chip control on cnc lathe
Post by: ostie01 on August 29, 2008, 04:10:41 PM
Hi, Normally, chip breaker is related with feed and RPM. Very often, variation of feed and depth of cut by very little will make a huge difference.

If you work with a small lathe, try reduce depth of cut and increase feed. Do that until you get it right and get nice chips.

When working with aluminium, try to increase the depth of the chip breaker on the insert with a grinder.

But I think your best bet is to increase feed until you are happy with the result

Title: Re: chip control on cnc lathe
Post by: Ian Ralston on August 29, 2008, 06:08:34 PM
Chip control can big be problem in a production situation. Usually a change in material specification is the only way out. Have a look at:-

They show the chips from various grades of aluminium.
Sometimes it is possible to predrill a hole or cut a slot in the material, prior to machining, to give an interupted cut. This works well in stringy pastic (technical term :) )

Title: Re: chip control on cnc lathe
Post by: Hood on August 29, 2008, 08:44:24 PM
As has been said its all down to feed and DOC, different materials will require different settings and  even using different geometry tips can make a huge difference on hard to machine materials. When machining Alu it is often best to use tips that are specifically for Alu although I never do as I dont machine a lot of it (mainly steel and stainless) so its not worth the expense for me.
Title: Re: chip control on cnc lathe
Post by: guynamedbathgate on August 30, 2008, 08:57:02 AM
yeah I understand. I am using a small 9x20 Grizzly lathe I converted to cnc so speeding up the feed and keeping the program unchanged is out of the question. I am pushing the limit of what that little guy can do already and I would just get the death shakes out of it if I did that. I am machining a bunch of 6061 Aluminum.
When I first started machining Aluminum by hand a few years ago I used to think the long chips were kind of novel and I'd try and see how long I could make a single chip by setting the feed screw and then carefully pulling it across the shop as it un-spooled. Now i just want tiny chips... Like when I machine brass.
I actually ended up slowing the feed rate down a good bit. still getting less than desirable chip formation but it is more manageable but it has the draw back of making the program run about 80% longer. Its always a give and take with these little machines.

Title: Re: chip control on cnc lathe
Post by: jimpinder on August 30, 2008, 12:07:35 PM
You have my sympathy.

I set up my lathe, worked out feed and speed etc. and got some superb steel cuttings - as you say - about three feet long - in steel, and was congratulating myself on such a good set up, when the whole thing wrapped round the chuck, picked up some more swarf out of the tray and then proceeded to rip out the wiring to my limit switches. >:( >:(

I will adjust speed and feed  ;D ;D
Title: Re: chip control on cnc lathe
Post by: guynamedbathgate on August 30, 2008, 01:05:01 PM
haha yeah.
I had to disable my limit switches a while ago because the chips were just to much and I was always tripping them trying to remove the chips while running. Its not like they did anything anyway because more than likely the tool would crash into the part, not the chuck and limit switches dont really help in that regard.
 I think I have you beat though on tearing up some wiring. I was  working with  1/4'' aluminum stock and had it sticking waaaay to far out of the other end of the head stock. (I know, I know I thought I could get away with it) long story short, the whip beat the stepper motor that runs the tool changer in half and blew out the Gecko that runs it, Not to mention I almost crapped my pants. That was a $100+ mistake I'll never make again.
Title: Re: chip control on cnc lathe
Post by: M250cnc on September 01, 2008, 05:21:03 PM
Excuse me if i am talking rubbish, i haven't got round to cncing my lathe yet.

But what about G73 peck surely that will work ?

Title: Re: chip control on cnc lathe
Post by: jimpinder on September 01, 2008, 10:52:00 PM
I think G73 is a drilling routine, where the drill goes in a distance, then comes out to clear the flutes and goes back in again.

You are right, this is much the same thing, but we are talking about continuous cutting on a lathe, where you can, if you are set up "right" get one continuous 20thou thick sliver of swarf many feet long, The feed from the steppers is so smooth that there is no break in movement to stop the cutter "cutting", therefore you get one long ribbon.

Anybody know how the "big boys" combat this - there must be a method, otherwise CNC cabinets would look worse than that stadium in China.
Title: Re: chip control on cnc lathe
Post by: DAlgie on September 02, 2008, 01:15:52 AM
Chipbreakers built into modern carbide indexable tool tips don't work until you actually take a decent cut with them, most lathes under 13" don't have the rigidity to make these work at all. You can grind in a chip coiler as I do for boring bars sometimes, smaller boring bars also don't have the rigidity to take a big cut anyway, so the best you can do is to try to make the chip come out as a coil, which is more controllable and not nearly as dangerous. Grind a slot close to the leading edge of the tool tip that will force the swarf to dive down and then up again, this will force it to turn into a coil, but the downside is that the edge won't last as long.
Title: Re: chip control on cnc lathe
Post by: Hood on September 02, 2008, 02:22:56 AM
As I said earlier and DaveA has just said its Feed and DOC that will determine whether you get chips or streamers, do some experimenting. I did a test piece for Peter Homann the last day, because his lathe is small I wrote the code with only a 1mm DOC and spindle of 2000RPM and a feed of 0.25mm/rev and no problems with swarf streamers or birds nests. This was however in EN24 steel, if in Alu then probably would have had to alter the DOC and feeds. Also as I said tip geometry can make a huge difference, especially in stringy materials, if using HSS then you can grind a chip breaker in similar to what Dave has just said, with carbide you shouldnt need it if you get the feeds and speeds and DOC right.