I've been battling with a couple of thinwall 3 1/2" deep bores all week in my spare time. It hasn't gone well.
Material? Thickness of wall? Diameter of bore? Tolerance? Fighting chatter? Through bore, or to a shoulder?
I normally use brazed carbide boring bars and when sharpened right they aren't bad but they require a lot of pressure and high rpm.
That's because they generally lack proper geometry for free machining. If readers come away with nothing more than the understanding that a proper chip breaker changes the way a tool performs, almost always for the better, each will have learned a valuable lesson. Relief angles on tools play a far less important role than some may have you believe. What really matters is how the tool sees the work-----rake. It also often dictates tool life----so there are times when one must compromise.
I've got one of the bars for HSS that uses a short piece of 1/4" toolbit sticking out at 90*. I've tried a lot of different profiles but haven't had the success I should. I think I know what you will say...I should grind a narrow chipbreaker groove along the length of the short bit...correct?
I'm inclined to say yes, but without knowing more, I hesitate. Thin wall work can be exceedingly tricky---whether you're turning or boring. I'd want to know a lot more about your setup, including the nature of the bar, diameter (of the bar) , if you're running on center, speeds and feeds, and, of course, what material, what tolerance, and what kind of surface finish you're trying to achieve. Sort of a repeat of the above things I mentioned. It's all important if you're trying to solve the mystery. Some things can be unreasonable and make the task border on the impossible without addressing the job from a different perspective.
That's what you told me for a facing tool for alu and it worked well. I never thought of doing this with a bit for steel.
That's the beauty of chip breakers. They work on almost everything----although hard materials shorten their lives considerably. Tough materials can yield surprising results, however. It's important that you understand the difference between hard and tough. They're not the same thing.
The nature of chip breakers for steel as opposed to aluminum would be a slight reduction of rake angle----and if the machine is light duty, width and depth may have to be adjusted accordingly. A shallow cut with fine feed would require a narrow breaker, and shallow, in order for the chip to curl. By contrast, a deep cut with heavy feed would require a wider and deeper breaker. Rake angle may have to be altered to prevent edge failure----which can be accomplished by using a larger radius for the breaker. As the radius increases, the angle diminishes, and it isn't nearly as deep. These features are best determined by trial and error, so the tool suits the exact conditions in which it's being employed.
I'm getting a very rough finish....my point is too sharp. I keep getting the nose a bit rounder but it's still not nice. I theenk I'm going about it all wrong. I've been using a typical 60(ish) deg profile with the point sticking out the side. Have a decent chip breaker ground in it but it's looking wrong now that I see your.
If you try something that resembles a tool in my post and are still having trouble, post a picture of your tool and lets see if we can figure out what the problem is. I agree----you're probably going about it wrong, but that's how we learn. You should build a strong, lasting impression of what doesn't work from this experience. It's all part of arriving as a machinist.
Harold...Sorry for the time lapse...been very busy.
The pieces I'm trying to bore aren't a "deep" bore as you would imagine...they are just deep to me....cuz of my noobness...lol!
It is 2" sch40 pipe(2.20 od if I remember right). The bore is 4 1/2" deep.The final wall thickness is .090.
I have about 3" sticking out of the chuck. I turned the od first....maybe not right but I wanted to see if it would distort before going any further.
I'm a bit handicapped with my lathe(14X40 Asian junk). The fine feed is .008 per rev but I am getting decent finishes with properley shaped cutters on the OD.
The finish inside these is very rough. Hoping to get a tool ground up like yours tomorrow. I've built a cutter/endmill grinder gadget and want to try freehanding on it. The thin edge cup wheel should work well. I'd like to make an adapter for Zip cut discs that I use on my angle grinder. They might work well for that chip breaker.
I'm sure if I follow your direction it'll be much better than what I have now.
I'll let you know.