# Carbide insert lathe tooling



## kuksul08 (Jan 31, 2012)

I've noticed a lot of people using the carbide insert tooling, with the triangular or diamond shaped removable cutter. I know this has been discussed here a lot since I have been reading the past threads. It's a bit overwhelming though. I'm doing hobby work and can't decide what is reasonable for me.

They make more sense than all the other cutting tools I have since you can turn, face, thread, and bore delrin, aluminum, and steel with a single tool. I am a little frustrated by the old I have that came with my lathe, some give nice shiny finished and some give a ridged, dull finish. So, a new tool is in order.

What are the _basics_ and where do you all source the holders and inserts?


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## precisionworks (Jan 31, 2012)

Small machines do better with positive inserts. Usually the second letter in the designation, like TPG, TPU, but sometimes well hidden like CCMT. The best single source for smaller machine tooling (IMO) is Curt at Lathe Inserts - great prices backed by a ton of knowledge & a nice guy to deal with. .

LatheInserts.com


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## Th232 (Jan 31, 2012)

precisionworks said:


> Usually the second letter in the designation, like TPG, TPU, but sometimes well hidden like CCMT. The best single source for smaller machine tooling (IMO) is Curt at Lathe Inserts - great prices backed by a ton of knowledge & a nice guy to deal with. .



Out of curiosity, this is something I've always wondered about. In TPG and TPU, since it's a 3 letter designation instead of 4 letter, why is it only 3 letters? I presume that they've removed the 4th letter (geometry), but I've never known why...


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## precisionworks (Jan 31, 2012)

If there's a 4th letter it indicates groove or hole - since both TPG & TPU are clamp down inserts there is no 4th letter.

A good ANSI/ISO chart


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## kuksul08 (Jan 31, 2012)

Great info in that link^. I like the kits that Curt has put together, it makes it easier for someone like me. Thanks.

edit: So I'm looking at the 3/8" hobby kit. Just curious - can you do boring with a square insert holder like that? I was thinking a round holder would work for most operations, but a square one is limited to external features.


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## precisionworks (Jan 31, 2012)

> can you do boring with a square insert holder like that?


The square shank holder has clearance under the insert for external operations only. Even a facing cut (which has the least clearance) allows free cutting action. A boring bar has a dramatically different shape with nothing but room under the insert. That allows it to be used for internal cuts.


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## unterhausen (Jan 31, 2012)

kuksul08 said:


> can you do boring with a square insert holder like that?


You need a boring bar. But to answer your real question, no, you can never stop buying tooling for your lathe


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## Th232 (Feb 1, 2012)

precisionworks said:


> If there's a 4th letter it indicates groove or hole - since both TPG & TPU are clamp down inserts there is no 4th letter.
> 
> A good ANSI/ISO chart



Thanks for that info. Looks like a better version of the chart I've got, never seen that "null" before. I presume there's no difference between nothing and "N" then?

And as unterhausen has noted, you can never stop buying tooling. Off the top of my head, if you choose to convert to carbide you'll need tools for:

* Turning. Recommend both left and right hand tools.
* Threading. Two, one for internal and one for external.
* Boring. Probably get a set of these.
* Grooving/parting. Might be able to get away with buying only one, but ending up with multiple widths (and an internal grooving tool) is a more likely scenario.

Then after that you'll realise you could get a nicer surface finish by having a tool that takes a round insert, or maybe you'll get different grades of carbide or coating for Al and steel.

Now... to find someone who sells CTAPL 08 and CTEPL 08 holders and ships to Aus at a reasonable rate...


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## precisionworks (Feb 1, 2012)

To start with, a right hand turning tool (cuts toward the chuck) will do lots of ops. Add a left hand later if needed. My left hand tool gets used maybe 5% of the time.

Threading - start with external threads & get rock solid with the procedure. Internal threading then builds on external threading skills.

Boring - start with a bar sized for the work you plan to do. For flashlights (CR123 or 18650) that means 1/2" (12mm) diameter. For a tiny bar like that solid carbide is what you really need. Add larger bars as needed.

Parting - narrow inserts work better on a small machine. Something close to 2mm is a great size, and narrower parting tools are also available. 

Grooving is where you can spend a ton of money so shop around. Mesa Tools USA has some nice low-priced tooling: http://www.mesatool.com/#


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## kuksul08 (Feb 1, 2012)

I have to remind myself not to cheap out because I'll end up buying the proper tools eventually anyway.


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## Al Combs (Feb 4, 2012)

Barry, please forgive the noob question. I'm still trying to learn about indexable inserts without buying a Machinery's Handbook. In post #2 you mention the second letter of the insert's designation refers to whether or not it's positive. If the letter 'P' is positive, does 'N' means negative? I've seen that mentioned before and didn't bookmark it. But the ANSI/ISO chart in your 4th post say that a 'P' in the 2nd letter refers to an 11° clearance or relief angle.

Is there more than one type of designation for indexable inserts? Your ANSI/ISO chart is the most comprehensive on the subject I've come across. One of these days I'll figure it out.:shakehead


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## gadget_lover (Feb 4, 2012)

P and N tell you the clearance of the cutting edge. You need more clearance if the insert holder is going to tilt the insert because you still need clearance so the tool does not rub as it cuts.

The greater the clearance, the more you can tilt the insert ( or the tool).

Dan


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## Maglin (Feb 4, 2012)

Al Combs said:


> Barry, please forgive the noob question. I'm still trying to learn about indexable inserts without buying a Machinery's Handbook.



You really should get your self a machinery handbook. It's pretty invaluable and helps you make about anything. I would look at just getting a few tools to start off with that share a common insert. So you won't have a lot of different inserts to buy and stock. I like the CNMG inserts I think it is. They have no rake and require a good holder that presents the insert with a negative rake. This gives me 4 cutting edges per insert to use and I can use one tool to face, turn, rough & finish, and turn to a shoulder with a RH tool. For boring bars I went with the Shars set that was a good starting point. They use CCMT inserts just like the TMX tools that latheinserts.com sells. I would get at least 5 CCMT and CCGT inserts for cutting steel and aluminum. Being they only have 2 cutting edges because they are a positive rake insert you might want to have 10 of each.

I personally like using HSS lathe tools. It doesn't cost near as much when you chip one as you can resharpen it and also kept a keen edge on it with a oil stone. I tried out the Diamond Tool Holder which is a really cool idea and works very well for the hobbiest. You don't have to know how to sharpen tools just one edge which you have a fixture for. You can put a .250" round bit in it and it's a finishing tool that gives a very good finish. With a .250" square tool it's a roughing, turning, facing, and turning to a shoulder tool.


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## precisionworks (Feb 4, 2012)

+ 1 on Machinery's Handbook. It is helpful in every area of machine shop work. You will not find more useful information in any one volume.


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## PhotonFanatic (Feb 4, 2012)

Al Combs said:


> Barry, please forgive the noob question. I'm still trying to learn about indexable inserts without buying a Machinery's Handbook. In post #2 you mention the second letter of the insert's designation refers to whether or not it's positive. If the letter 'P' is positive, does 'N' means negative? I've seen that mentioned before and didn't bookmark it. But the ANSI/ISO chart in your 4th post say that a 'P' in the 2nd letter refers to an 11° clearance or relief angle.
> 
> Is there more than one type of designation for indexable inserts? Your ANSI/ISO chart is the most comprehensive on the subject I've come across. One of these days I'll figure it out.:shakehead



Try this page at Carbide Depot.


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## Al Combs (Feb 6, 2012)

Thanks guys.


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## kuksul08 (Feb 6, 2012)

I'm a little confused about the part off tool inserts. They are really small, looks like you could only go 1/4" deep, and I'm not quite seeing how they are secured in the holder.

The problem I am having now is that my parting tools are HSS, .050-.125 widths, and when they cut they flex and leave a sort of ugly surface finish. 

Any insight on these?


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## gadget_lover (Feb 6, 2012)

If they flex you probably do not have the tool at exactly 90 degrees to the work. I use a machinists square to ensure the blade is exactly at 90.

And that tool you post there will go as deep as the cut-out allows. probably 1 inch.

Dan


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## pmath (Feb 6, 2012)

I've been remiss in acknowleding the help I got here directing me to Curt's inserts. I cannot believe how much better my tiny lathe works with these beauties.

Peter


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## kuksul08 (Feb 7, 2012)

Well, turns out I will _have_ to buy some new tools. I broke my only right hand turning tool as well as a left hand tool I was using for facing tonight. I was feeding into a steel bolt and I felt a little resistance, then suddenly the bolt walked up the cutter and chunked it before walking out of the chuck. What a nasty sound...

Now correct me if I'm wrong, but don't you need a left hand tool for facing and a right hand tool for turning? How are you supposed to face work with these insert holders since they are only right hand?


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## BVH (Feb 7, 2012)

IIRC, my right-hand tool is an SCLCR and uses an 80 degree diamond. I turn and face with it without changing anything. I face inside to out.


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## gadget_lover (Feb 7, 2012)

kuksul08 said:


> Well, turns out I will _have_ to buy some new tools. I broke my only right hand turning tool as well as a left hand tool I was using for facing tonight. I was feeding into a steel bolt and I felt a little resistance, then suddenly the bolt walked up the cutter and chunked it before walking out of the chuck. What a nasty sound...



Bolts are sometimes sneaky. You don't think about the way the threads reduce your contact area to 1/8 of it's normal amount (chuck to work). You are gripping it by the crests of the threads and they can deform under stress. A threaded sleeve sometimes makes the difference.



kuksul08 said:


> Now correct me if I'm wrong, but don't you need a left hand tool for facing and a right hand tool for turning? How are you supposed to face work with these insert holders since they are only right hand?



The insert holders come in left and right hand. I have sets in 1/2 inch shank and 5/16 inch too.

For facing you can even be creative and turn the tool-post to present the cutting edge of any tool to the work when facing. 

Daniel


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## kuksul08 (Feb 7, 2012)

I didn't even know you could face inside to out. Doesn't that mean you have to plunge a little bit near the center?

I broke one of the top style cutters. It's a Valenite brand. What I don't get is that the cutting edge doesn't stick out much, so it would be very easy to end up "rubbing" the material rather than cutting it, if it wasn't perfectly on center or below. Maybe I'm just a complete noob.


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## Th232 (Feb 7, 2012)

kuksul08 said:


> What I don't get is that the cutting edge doesn't stick out much, so it would be very easy to end up "rubbing" the material rather than cutting it, if it wasn't perfectly on center or below. Maybe I'm just a complete noob.



Stability. Material underneath to support the cutting edge means it flexes less and is stronger in general. When I started out with my lathe, I was surprised at how much force was exerted on both the workpiece and the tool.

Try this:
1) Hold out your forearm so that it's horizontal with nothing under it, and drop a heavy object into the palm of your hand.
2) Forearm horizontal again, but this time support it (e.g. lie it on a desk) and drop the same object into the palm of your hand.


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## KC2IXE (Feb 7, 2012)

kuksul08 said:


> ...snip...What I don't get is that the cutting edge doesn't stick out much, so it would be very easy to end up "rubbing" the material rather than cutting it, if it wasn't perfectly on center or below.



And WHY would your cutting edge NOT be exactly on center? If it isn't on center, time to stop, and adjust your tool post ASAP


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## precisionworks (Feb 7, 2012)

> And WHY would your cutting edge NOT be exactly on center? If it isn't on center, time to stop, and adjust your tool post ASAP


+1

For outside turning or facing set the cutter at dead center (although some tools work even better .005" lower).

For inside work like boring or threading set the tool .010" above center.

At least that's what I do :devil:


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## kuksul08 (Feb 7, 2012)

I must have not had it on center then. Rookie mistake I guess, not taking the time to set it up properly.

I'm looking for a guide to setting up the cutting tools. I always have the edge of the tool 90 degrees to the work, but that's not always what I see in practice. For example, if I was leading with the tip of the cutter (a negative side cutting edge angle?) it will be slightly undercutting the next chip. Is that a good or bad thing? A lot of questions like this come up when I'm working on it, and it would be nice to know what types of angles are best for different cutter geometries and material types. Will the Machinery Handbook cover this information on a basic enough level?

edit: Another thing I'm curious about is why some people choose C- inserts, an 80 degree diamond with 2 cutting points, and some choose T- inserts, triangular with three cutting points. It seems like the T would be tougher and you could even do threading with it. You can still get down into a corner with them too.


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## gadget_lover (Feb 7, 2012)

There are many different designs because each has an attribute that has some value. 

The 60 degree triangle is stronger, so it's a better candidate for rough work. You get either 3 or 6 cutting points and it's easy to make a tool to hold one. As mentioned, it can also do a decent thread. It's also the easiest to recognize on sight for newbies. 

The 80 degree diamond, on the other hand, only gives 2 (or 4) cutting edges BUT, you can use the same tool to do turning and facing without even moving the tool. The smaller point requires less power to cut the same depth, though it takes a smaller bite. 

I recently discovered the way that a round insert allows a surface that is almost polished. The radius on a 1/3 inch disk is really broad and barely leaves a trace of a groove. 

Eventually you will find a use for as many inserts as you can buy.

Daniel


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## gadget_lover (Feb 7, 2012)

kuksul08 said:


> I always have the edge of the tool 90 degrees to the work, but that's not always what I see in practice.
> 
> < snip >
> Will the Machinery Handbook cover this information on a basic enough level?
> ...



Yes, the MH will give that info, but you have to find it. In general the right turning tool will present at something like a 20 degree angle. Imagine the triangle pointing straight ahead. Now rotate it about 15 degrees and cut from right to left. 

The ones you have in your post are for turning to a shoulder, so the cutting edge is typically at 90 degrees to the axis.

Daniel


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## darkzero (Feb 7, 2012)

gadget_lover said:


> The 60 degree triangle is stronger, so it's a better candidate for rough work. You get either 3 or 6 cutting points and it's easy to make a tool to hold one. As mentioned, it can also do a decent thread. It's also the easiest to recognize on sight for newbies.
> 
> The 80 degree diamond, on the other hand, only gives 2 (or 4) cutting edges BUT, you can use the same tool to do turning and facing without even moving the tool. The smaller point requires less power to cut the same depth, though it takes a smaller bite.
> 
> ...



Daniel, don't you have that backwards (aside from the amount of cutting edges)? 

An 80° diamond is stronger than a 60° triangle & generally the 80° diamond shape would be better for roughing than the 60° triangle shape. The 60° triangle would have a smaller point (not relating to corner radius) which would allow less machine power, but more prone to chatter/vibration, & not able to take as deep of a cut as a 80° diamond. Reasons why they're more popular with smaller lathes & why it's not common to use 80° diamond negative inserts with smaller lathes.

I also didn't know you could use a 60° triangle "T" insert to cut threads, I always assumed the corner radii that they were available in were too large.




kuksul08 said:


> Another thing I'm curious about is why some people choose C- inserts, an 80 degree diamond with 2 cutting points, and some choose T- inserts, triangular with three cutting points. It seems like the T would be tougher and you could even do threading with it. You can still get down into a corner with them too.



It's nice (& better for your wallet) to have more cutting edges that the 60° triangle will give you over the 80° diamond but the 80° diamond shape in both positive & negative as well as the round inserts are my favorite. Second would be the 55° diamond followed by 60° triangle for profiling. I like the 80° diamond the most because it's very versatile, has good strength, & I use both negative & positive so they cover most of my needs. Like Daniel stated round inserts are a awesome & when the edge dulls all you need to do is turn the insert ever so slightly for a fresh new edge. One insert should last a very long time as long as you don't break it.

As long as you use the right insert for the job, a carbide insert can last you a very long time, & having more cutting edges per insert is not the factor I look for in an insert shape. For example, if you use a sharp positive CCGT insert to make roughing cuts in steel, chances are that insert is not going to last long or break & it's not the insert's fault. More often I change inserts because I chipped the edge rather than wearing it out.

You'll find out that there is no "all purpose" insert although many will say the CNMG insert would be the best canidate as long as you have sufficient power. I mostly use all sorts of 80° diamond inserts in different sizes, cutting angles, corner radii, & coatings in my most common operations. It's just what I found to use the best for me. I still don't know how to properly choose a chipbreaker yet.


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## gadget_lover (Feb 8, 2012)

darkzero said:


> Daniel, don't you have that backwards (aside from the amount of cutting edges)?



Mea Culpa. I was thinking of the diamonds ( 55 and 35 degree shapes) and not the CCMT. I think of the CCMT of as a parallelogram. The diamonds I was picturing have sharper angles.

The chart here lists the capabilities of the basic shapes.
http://www.carbidedepot.com/formulas-insert-shape.htm

The life of single edge of an insert is measured in hours. Using a small lathe means you spend more time cutting to get the same material removal.

Daniel


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## darkzero (Feb 8, 2012)

Gotcha, I see. :thumbsup:


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## Th232 (Feb 8, 2012)

darkzero said:


> I also didn't know you could use a 60° triangle "T" insert to cut threads, I always assumed the corner radii that they were available in were too large.



I've seen some TPG 220 inserts, which should mean no corner radius. On the other side, hellloooo stress risers?


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## gadget_lover (Feb 8, 2012)

I've found that the triangles are 'close enough' for general threading. If I was doing something that was structural in nature, I'd worry about getting the right inserts to avoid stress risers in the thread. For all practical purposes the slight radius of the '0' radius tip works well enough for me in small threads, and the '1' or '2' for bigger threads.

One of these days I'll get a proper treading tool and the associated full profile inserts. 

Dan


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## kuksul08 (Feb 8, 2012)

Great info, I think that cleared up a lot for me. It's all taking me back to the hobby kit from Curt at latheinserts. He chose the 80 degree diamond with cutters for both aluminum and steel and now I know why. I assume is it best to get the largest size my toolpost will support for rigidity, which in my case is 1/2".

Also now I am understanding that you can't use the same holder for every carbide bit. So if I wanted to use a round insert for finishing, that would mean getting a round specific holder.


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## kuksul08 (Feb 14, 2012)

I recently bought a 3/8" SCLCR boring bar with a 21.51 (iirc) CCMT insert that came with it. The ad specifically said it would not come with an insert, but oh well. It appears to be TiN coated. Any idea what materials this is designed for based on the shape? It looks to me more like steel since it does not have a high positive rake for aluminum or plastics. Then again, it doesn't look negative either...


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## precisionworks (Feb 14, 2012)

The C (second letter) designates 7° clearance and is considered a neutral rake. 

On a CNMG the N indicates 0° clearance, while a TPU has 11°. The relief angle on the CCMT is 7° greater than a negative insert & only 4° less than a positive shape. 



> Any idea what materials this is designed for based on the shape?


That's a GP (general purpose) insert. You can find that shape in an aluminum-specific insert as well as many others.


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## kuksul08 (Feb 14, 2012)

Thank you


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