Trouble with parting off

Hey Allen it looks like most everything has been covered but one thing I thought i would mention, without knowing how big your lathe is and it not being really important would to buy a good insertable carbide cutting tool and match the insert grade for the application that it calls for, example would be to use a sharp tool with positive rake for soft materials such as aluminum or 1018 stuff that kind of machines like pink eraser, then an insert with a negative rake for harder materials or for an interupted cut something that requires more toughness rather than sharpness and when you get a good tool with a rigid setup close to the chuck and everything locked down apply a good cutting oil not coolant and when you start to push in feed it and i mean feed it I have a precision mathews 1340T I part 4140 heat treat 360 rpm .006 ipm feed and don't think twice about it. Good luck and keep banging away you will eventually get it

Justin Bowerman
JB Enterprise
07 ffl in central CA.
 
Thanks lads for even more information, how can I go wrong now :)

Just a little question for Zideuner, what is a small chip breaker cut in the top, can I do this myself.

Should have mentioned this before I suppose, my lathe is a Seig C3 the one with the brushless motor.

Alan
 
AlanP link=topic=2803.msg19764#msg19764 date=1311630494 said:
Thanks lads for even more information, how can I go wrong now :)

Just a little question for Zideuner, what is a small chip breaker cut in the top, can I do this myself.

Should have mentioned this before I suppose, my lathe is a Seig C3 the one with the brushless motor.

Alan

Hello,

By chipbreaker, I mean a small arc just behind the upper tip of the parting tool. The tool is on an angle of about 30 degrees at the end. You really don't need a chip breaker, but I find it to be helpful. See the picture. The arrow is pointing at the area that I cut away on a grinder. Works for me. ;D

The main thing is to go slow and feel the cut in. Just yesterday I parted off a spacer from a piece of 1" HRS. It had a 3/8" hole in the center so I only had to cut through 5/16" on the side. This still took me about three minutes. I go very slowly and seldom have trouble parting off. Others may work more quickly but when I trry to speed up, the cut has a tendency to dig in. It it digs in hard enough it will break the tool and may even throw it at you.

I buy my parting tools from CDCO. They have a holder that is about 3/4" high and will take a 1/2" tool. Since I have BXA tools, I had to cut one of my BXA holders to take 3/4" tools to fit the CDCO toolholder. This is also useful for a whole drawer full of 3/4" tools that I bought surplus used. (The BXA holders will take only 5/8" tools and I'm going to mill a couple more to take 3/4" tools,)

I find it more practical to set the tip just below the center of the piece and, as I said, I run at one of slower speeds on the Enco 13 X 40, 115 rpm. There's no hard and fast rule, however. If it works, do it.


PartingTool.jpg
 
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Thanks for explaining that Zigeuner. (nice drawing :))

What a wonderful site this is

Alan
 
AlanP link=topic=2803.msg19862#msg19862 date=1311705763 said:
Thanks for explaining that Zigeuner. (nice drawing :))

What a wonderful site this is

Alan

You are welcome! :)
 
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Yes,get rid of the top rake. It is making your cut off tool too aggressive.
 
I'd be careful with the chip breaker unless it's VERY small. Your lathe may not have the rigidity to handle the tighter included angle between the cutter and the workpiece making it prone to grabbiness.

For small lathes (or big flexible lathes like my Atlas), best bet is to keep it flat along the top with no chipbreaker. I hate to disagree with Zigeuner, but his Enco lathe is a brute compared to the C3 and what works for him could compound your problem.

Do get a P cutter. You'll be glad you did.

John
 
jgedde link=topic=2803.msg19891#msg19891 date=1311726219 said:
I'd be careful with the chip breaker unless it's VERY small. Your lathe may not have the rigidity to handle the tighter included angle between the cutter and the workpiece making it prone to grabbiness.

For small lathes (or big flexible lathes like my Atlas), best bet is to keep it flat along the top with no chipbreaker. I hate to disagree with Zigeuner, but his Enco lathe is a brute compared to the C3 and what works for him could compound your problem.

Do get a P cutter. You'll be glad you did.

John

I'm deeply offended. No one has ever disagreed with a single word I've ever typed and posted on the internet before. I'm speechless. ;D

The Enco does have a bit of heft to it. It made short work the other day of tapering a couple of car axles which had been annealed on the ends.

I've been using and experimenting with various types of tools for some 15 years now and I've come to the conclusion that there is more than one way to do things. Parting off is one of the most difficult of processes to do on a lathe. I've seen many threads where people have trouble with it. I've got it under control at this point. It's a matter of experimentation.

Suffice it to say that one should use or not use a chipbreaker as the case may be depending upon your equipment.
 
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I use a flat top "T" shaped cut off for everything. It has a hollow grind across its width,so I don't want to disturb the top of it.
 
David Utidjian link=topic=2803.msg20030#msg20030 date=1311822089 said:
Aside from what others have said: You are cutting brass. For brass all your tooling should be neutral rake or even negative. On your C3 neutral top rake (0 degrees, or flat-across-the-top) is what you want. Same thing goes for boring, threading, turning and drilling of brass.

When you get to steel and aluminum it is different again. For steel you definitely want some positive top rake.

Zigeuner,

I would be very surprised if your parting tool design works well for brass.

-DU-

Well, you have found me out.....You have made me confess that I have more than one cutoff blade. You are a very intuitive fellow. LOL.

Yes, of all of the metals, for some reason, it's in a special class. if the operator isn't especially careful, the tool will dig in very quickly and make a lump inside of the cut that will break the tool off on the next revolution. A flat tool will work much better.

That said, the main thing that I've found is to keep the speed down and "feel" the cut. That's every bit as important as the shape of the cutter, although as you said, you have to be careful with brass.

It Makes me wish that I had room for a lathe in the class of the 8,000 pound, 20' X 72" Monarch lathe that my neighbor/professional/machinist friend has in his shop. Beaides being able to rip off half inch (.500) cuts in steel (yes, I've watched this done), it will part off at almost any speed you want. So, the other element is rigidity. The difference is noticeable.

So much machinery, so little time. (Sigh)
 
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