Tool Geometries For Lathe & Mill Explained - Great Video Tutorial

Tony

Thank you for the specific recommendations. Sometimes it is hard to get a recommendation and a reason why explanation.

So if I can interpret the code - CNMG
C = 80 degree diamond shape and D = 55 degree diamond
N = 0 clearance angle (what is the benefit of zero relief angle? Is this related to the chip breaker being on both sides?)
M = tolerance of production specs - (is this a very common, therefore read more cost effective standard to accept?)
G = Hole in tip and a chip breaker on either side - so you can turn it upside down?
43 = so the 4 relates to the inscribed circle size for a diamond shaped tip of 12mm? and the 3 describes thickness (4.76mm for ANSI code or 3.18mm if the code is an ISO code).
x = the variable which defines the radius of the nose of the tip???? So a number smaller than 2 means a radius of less than 1mm and numbers larger than 2 a radius larger than 1mm

So a tool designed to hold a C shaped tip is only ever able to hold a 80 degree diamond shaped tip - no exceptions?????

So one of the things I don't get yet is clearance angle. I see that they seem to range from 0 degrees to 30 degrees. What determines which one you choose?

Thanks in advance for your assistance.


Mal
 
In a nutshell, you got it. The other angles are built into the holder, for the most part. The insert, if you look closely, can be had with a totally flat top and bottom. No chipbreaker, no nothing. Limited use. There can be and for most materials should be a chipbreaker molded or pressed into the top. These 80° inserts provide 4 cutting edges, also. If you wanted to use the 100° "corner" there are toolholders as well as face mills that will use those. Of course, being over 90°, you cannot face/turn or mill to a square shoulder, but they have their uses, definitely. The clearance angle you refer to is basically the "tilt" of the insert in the holder. This is done two ways. One is simply the angle the insert pocket is machined in the holder. The other is the choice of seat that is under the insert. Not all holders use seats, but some do. You do have to consider the clearance angle of the holder when choosing the insert, because the rake angle can be changed (for better or worse) by that seat angle. My choice is a neutral seat and a slight negative holder. If then, I really need a positive rake, I can get that on the insert. I don't think I have ever needed to, however.

Yes, a holder for a C profile will only work with that style, and whatever size it is made for. Since you said you could hold a 25mm holder, I recommended a common insert seen in that size. IMO, for OD work you won't need anything smaller, since you can get small corner radii, and even though you can get a larger insert, there's little point unless you plan on doing a lot of roughing and even though you have a healthy sized machine, you would never get the max performance from anything larger.
 
Bob Korves said:
Good, informative video. Unfortunately, it can also give a novice viewer the idea that you need a PHD in cutter design and racks with thousands of tooling and insert choices. Bear in mind that all those choices are there to optimize manufacturing machining, and have little place in the home shop beyond understanding their principles to help get the best out of what you have. For us, if we need a special shape of tool, we can grind it from HSS. We can also standardize on one or a few insert and holders sizes and shapes that are versatile for our needs. There is a mountain of things to learn about all this, but the basics can help us choose wisely for our home shops. We can even use the tooling that has been superseded in industry, and is now available used and cheap. Just be very careful not to get tooling that requires too much power or rigidity for our smaller machines. A 8" negative rake face mill is not a good choice for a bench top mill, and a 1" shank insertable holder is going to be difficult to fit and power on your 9" lathe. Do some study before buying your tooling and make sure you understand what it is you are buying and how it will work for your needs. Also make sure you can still get useful inserts for any tooling you are contemplating. Some are very expensive or obsolete.
Click to expand...

A clear and concise response to the video with respect to hobby machinists. The effects of rake angles and power requirements can be helpful as well as nose radius.
Thanks Bob.
 
Thank you Tony - As much as I would like to avoid duplication in my tooling and would prefer versatile tooling which gives me options I don't even know at the moment I will want later - I can see I will just have to jump in the deep end and splash around - that means I keep learning and will inevitably end up finding out later I could have made more efficient decisions if I had known more.

and this is just the lathe - the milling machine is another beast all together.

I have made up a sheet in Excel for inserts and another for boring bar tools which explain all the language - that is helping me get an overview of the system
It will work out OK
 
The video is good at explaining the basic meanings of the inserts and tool design parameters. The diagrams are especially informative.
What I have yet to find is an informative commentary on which tools to choose and why they are a good choice. We probably don't need a thousand tools - fine.

However should I choose a triangular shaped insert or a 80 degree diamond insert (and tooling to suit) as my general go to combination?
Do I need both and if so which one is the best to start out with?

When and why should I choose a negative rake or one of the other options in the positive rake options. I got advice from one tool supplier to go with a negative rake in a toolholder which is also negative rake.
Is this because, if I am listening right, a negative rake is more robust than a positive rake (stronger tip geometry) and therefore more forgiving - or am I missing something?
I am a sort of a "middle of the road sort of guy" - so I guess I would have chosen a 5 to 7 degree positive rake - not negative but not aggressive like 30 degrees - what would be the downside of such a decision?

And the questions are endless and suppliers just don't have the time to put up with my questions.

So advice on a good source of commentary on the whys and why nots of tool selection would be appreciated.


Regards


Mal
 
A lot of the choices made by pros are so they can get a good finish along with good chip generation. They look for tight curled chips that break into very short shards, and then fall into the chip pan instead of their hair, shirt, or face. If you have to stand in front of a machine all day, every working day, then those factors become more and more important. There are lots of tools that will remove metal satisfactorily, but many are not pleasant to use on specific jobs for various reasons. Chip generation is only one factor. Getting into tight places is another, keeping heat out of the work is another, insert life is another yet, etc., etc. There are lots of factors, and it takes experience to even learn about the issues, much less all the ideal solutions for myriad situations. Make friends with a good job shop machinist with tons of experience in a wide range of work, and buy him his favorite beverage on a regular basis while you talk...
 
Bob, I think you have made a very good point/points. I know a few folk who may qualify, but they don't want to talk work (even with plenty of Beveridge) - I will have to keep looking and hanging out with Uncle Google while I wait.


Mal
 
Mal,

The triangular inserts seemed to be the place to start for me. After studying up on cutting tools I concluded that my best strategy was to investigate what was needed for a specific job.
Eventually you get tooled up for the jobs that you actually do.

It was also easier to get free advice on a particular problem or job than to get a dissertation on the virtues of different tools designs.

As Bob mentioned there is a myriad of considerations and even a seasoned job shop operator might need to consult with a tool supplier on occasion.

It became clear to me that buying tools is an on going thing and like with everything else it takes a bit of experience of our own to see what we need more clearly.

This place provided some useful knowledge: http://www.sandvik.coromant.com/en-gb/pages/default.aspx

It was also interesting to spot what tools were being used in instructional videos (the professional ones). For example: http://www.thatlazymachinist.com/my-shop-videos.html
 
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Nice to hear from Canada, thanks for your comment.

I keep hearing the long timers bashing on (no disrespect intended) about HSS and sharpening your own tools. While I have done a very small amount of HSS tools ground by my own fair hands, I will admit the knowledge that went into the process was miniscule - I have always used it as a last resort to build specific form tools and always for aluminium, plastics and brass, not steel or stainless.

So today I am heading off to my local tool supplier and I am going to grab some HSS and get my old head into low gear and start learning to grind, measure and test some cutting angles - so I can better understand what works and why.

That does not mean I will abandon inserts and holders - however I am going to enter into that Aladdin's cave of jewels with a more circumspect eye and a credit card limit set.

Now I will just pop over and check out those links you supplied - lots to learn, better get on with it.

Cheers from Downunder

Mal
 
malmac said:
Nice to hear from Canada, thanks for your comment.

I keep hearing the long timers bashing on (no disrespect intended) about HSS and sharpening your own tools. While I have done a very small amount of HSS tools ground by my own fair hands, I will admit the knowledge that went into the process was miniscule - I have always used it as a last resort to build specific form tools and always for aluminium, plastics and brass, not steel or stainless.

So today I am heading off to my local tool supplier and I am going to grab some HSS and get my old head into low gear and start learning to grind, measure and test some cutting angles - so I can better understand what works and why.

That does not mean I will abandon inserts and holders - however I am going to enter into that Aladdin's cave of jewels with a more circumspect eye and a credit card limit set.

Now I will just pop over and check out those links you supplied - lots to learn, better get on with it.

Cheers from Downunder

Mal
Click to expand...

Mal,

Like you, I am definitely an amateur hobbyist, so I am in a continuous learning mode. I've gone through the same dilemma as you are with selecting appropriate carbide insert tooling. After about five years of off-and-on experience, I'm not sure I would even go with insert tooling if I were starting over again, with the one exception being threading. In my experience I have found that the carbide works well when using high rates of speed and feed. I typically have a difficult time getting a nice finish with carbide and always seem to revert back to HSS for a nice finish. I was just doing a little project yesterday machining some 4130 and used carbide for the roughing operations and then went to HSS to finish. I think for hobby machining, HSS will perform well at a much lower cost. You may want to work with HSS for a while before you decide whether to invest in the carbide insert tooling. Just my opinion and it's probably worth exactly what you paid for it.

Ted
 
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