Carbide Turning Inserts, What flavour do you prefer?

[Ueee]

Hi all,
In the diamond tool holder thread an interesting discussion started about CCMT and CCGT inserts. I have been meaning to start this thread for a while and said discussion reminded me about it.
So i'd like to know, what do you use for external turning and why?

I still use the first holder i got, an iscar MWLNR, which holds WNMG 06T3 inserts. This was sold to me by my local shop when i first got my lathe. These holders have 5deg negative rake both axially and radially. The inserts have 6 points but generally you only get 4 or 5, by the time you knock a corner off and it chips right down to the opposite side.:doh:
I have just finished a box of WNMG 06T304 PP (positive rake) IC9250. The 04 is the nose radius, .04mm. The have cut well and given decent surface finish at 150m/min and at least .6mm DOC. The biggest problem is cutting to size trying to take such a cut on a small lathe. Generally the best i can do is get within .05 this way. Trying to take a little .05mm cut leaves an appalling finish of course.
I just bought a box of 06T308 TF (changing rake angle along the edge) IC8025 inserts. They are not as tough as the 9250, but the nose radius makes up for this somewhat. These seem to excel at facing but need really good rigidity for general turning. They do however give a great finish at a lower DOC. The pic below is of progress on an ER40 collet chuck, diameters and 70 and 50mm. The finishing cuts were done at 1250rpm DOC .2mm.

I have some GN (general) inserts in the mail, and am trying to find some SF (super finishing) ones to try.

The only other inserts i use are CCMT in a small boring bar, but i'm sticking with OD turning for now.

Cheers,
Ew

[Michael G]

I use CCMT's in both my external holders as well as the larger boring bars. The small boring bars take CPMT inserts. These were recommended a long time ago as a good "general" insert, and a way of minimising insert costs as I wouldn't have to have a different insert for each holder.
Lately I've been considering experimenting with different brands and grades to see if I can get a better finish/ life etc. I think that some seem to chip/ spall more readily than others, although that is a small sample size and would be highly grade & job dependent. Maybe I'll have an answer in another 3 to 5 years.
I think the key thing is to have a solid lathe. The previous lathe was not very rigid and both the inserts and the finish suffered for it.

Michael

274794

[Anorak Bob]

Other variables enter the arena Ew.

Material being turned and horsepower along with coolant or lack thereof. And then there is the eye of the beholder. A finish one person feels is acceptable another may find not so.

I purchased a Kennametal toolholder yesterday (an expensive whim purchase :- ) and was given a copy of Kennametal's cutting tools Master Catalogue. Probably a thousand tissue thin A4 pages. A quick look revealed that they offer 27 different styles of chip breaker on their turning inserts. Kennametal's High Positive inserts work for me but to find out if their roughing, medium, finishing or universal positive inserts work with a piddly low powered machine, requires a financial outlay and one that could well end up as money wasted. And then, of the 41 different grades insert grades available, probably only one, their KC5025 grade, is best suited for my small lathe. Spent some dough finding that out too.

*** A note for Ray should he read this and become concerned. The pair of black CCGT HP inserts I sent are KC5010 grade. They are harder than the 5025's, more brittle but provide an even better finish, so I was advised yesterday.

BT

[cba_melbourne]

There is exhaustive and excellent free literature available from carbide tool makers. This is invaluable information for industrial class lathes (heavy and rigid and powerful and capable of high rpm and using flood coolant).

But if you own a small hobbylathe (something up to the size/weight/power of a Hercus 260 I would nowdays cosider a hobbylathe) you need to understand, that much that is published by carbide tool makers does NOT apply to you:

- Hobbylathes need SHARP tools. They cannot cope with the cutting forces generated by purposedly blunt tools as used in industry. In industry, many carbide tools for roughing do shear, not cut. Shearing produces good surface finish and the inserts last a long time, but needs high speeds, high power, flood coolant and very very rigid heavy machines.
- for this reason, negative rake carbide tools do not perform well on hobbylathes. This means you cannot use the very economical low cost type of inserts, that can be flipped over upside down to double the number od cutting edges.
- most hobbylathes do not use flood coolant, and cannot reach the sort of spindle rpm needed to make carbide inserts last as long as in industry. Without flood coolant, carbide inserts must be used dry. Drip or brush-on coolant is a bad idea, as it shocks the cutting edge and causes microcracks, that shortens useful life even more than using dry.
- coated inserts are of little use on hobbylathes, on the contrary the coating always means a less sharp cutting edge. On a hobbylathe there is no difference in life between coated or uncoated, life is in both cases much shorter than in industry. In some cases a coating can help with certain materials build up on the cutting edge, but in a home shop its generally not worth to stock coated inserts just for this.

What I can recommend for hobbylathes are positive rake insers such as CCMT 06.xx.xx (and DCMT and TCMT) for general use on steel, and polished inserts such as CCGT-Alu (and DCGT and TCGT) for general use on nor ferrous materials including plastic and wood as well as fine finishing to exact tolerance dimensions of steels including stainless. Whether one chooses diamond shapes (C)or triangular shapes (T) is rather irrelevant, just buy a complete set of toolholders for your choice. With such a set, you probably cover 80% of all tasks (less parting, grooving, and small size boring, and form tools). For parting I highly recommend a carbide insert blade. Chris

[rodweb]

I started with triangular inserts from H&F but recently purchased some CCMT's. I like them a lot better and have left, right, neutral turning tools and some boring bars. Some are 6mm and other are 9mm inserts. One advantage is you can turn and face with the one tool so the right hand CCMT is on the tool post by default.

i got an insert parting tool on Friday and gave it a run today and was happy with it but I was using coolant. I did not slow down like I do with a HSS parting blade and ran it at 500 rpm on a 14mm cut. My lathe is a AL320g with 13" swing so it has plenty of grunt.

Most of my tools come from CTC tools in Hong Kong.

[Ueee]

Thanks for the info guys.
It is a bewildering world of carbide out there, and like Chris says, its mostly not aimed at the smaller machines. And thanks Chris, another very well written and thought out post.

Bob, whilst i am aiming to find that mythical low DOC magical finishing tool, and of course there are so many variables that effect this, i just wanted to get opinions of what worked for who and why. As i stated i have only ever used 1 shape of general turning insert and i have better things to blow my money on than trying many others just to see what works.

So far the CCMT looks like a popular choice. Anyone else use any other different shapes?

Michael, what lathe did you have before the CVA? I think your right, it takes time to trial inserts and "get to know" each one and how to make it work.

Cheers,
Ew

[Steamwhisperer]

Hi Ewan,
if it is that magical finishing cut you are after, have you tried a HSS shear tool?
The finish is most acceptable :)
Here is a video that shows it.
Metal Turning with Contrary Tool.mpeg - YouTube (http://www.youtube.com/watch?v=hAF3Y5cR9z0)

Phil

[matthew_g]

Well guy's I like to be different it seems:p
But at least 50% of my tooling is the CNMG
For those that don't know it's the large common diamond shape.
I have at least 30 CNMG holders all in different head angles, Sizes and profiles. The thing I like about them is they are readily available from anywhere as they are a common industry insert. They are tough (i think allot of that is due to their shape) And they are quite acceptable price wise(very acceptable actually) They can often be found for under $40 for a 10 pack on the evil bay.

I have many many other shapes and style of holder and insert, But I always seem to fall back to using the CNMG holders and inserts.

Matt

[Michael G]

Michael, what lathe did you have before the CVA? I think your right, it takes time to trial inserts and "get to know" each one and how to make it work.


It was a Dai-shin P4 (7x14 from memory) - a Taiwanese bench lathe, '70s vintage. H&F sold similar as the parts were interchangeable. I moved on because I wanted some larger for the things I was doing and with a top speed of 1000rpm it did not have the speed or grunt to use inserts properly.

Michael

[pippin88]

I'm using DCMT070202 inserts in 12mm shank holders on a 7x14 mini lathe. I think they are great. Got them from CTC tools. I have converted the lathe to CNC however.

[Anorak Bob]

http://www.woodworkforums.com/attachments/f65/274794d1367959826-carbide-turning-inserts-what-flavour-do-you-prefer-p1010634-medium-.jpg

Michael,

I'm wondering what you are using to hold your workpiece. A small 3 jaw with internal jaws? And what is the function of the set screw? Some cam lock thingo?

Bob.

[pipeclay]

I would think he has either a D14 or D13 direct mount piece of stock going directly onto his lathe spindle.

Looks as if it is for some type of purpose made tooling to fit the camlock spindle.

[Anorak Bob]

I would think he has either a D14 or D13 direct mount piece of stock going directly onto his lathe spindle.

Looks as if it is for some type of purpose made tooling to fit the camlock spindle.

OK. Looking at it a bit closer it does seem like a one piece affair, not a chuck holding a workpiece.

[Bryan]

My guess is he's making a camlock adaptor for a dividing head.
Or maybe a collet chuck.

[Michael G]

Yep. Home made ER40 Collet chuck. Directly mounts on the D1-3 camlock

Michael

[Anorak Bob]

Here are (will be) my go-to turning tools. All the inserts are Kennametal High Positive KC5010 grade. The triangular insert on the boring bar did a nice job initially on the toughish steel CTC use for their arbors but suffered from fine chatter when creeping up to the required finished size. Probably more to do with the bar extension and subsequent lack of rigidity than the insert. The insert in the tool in the QCTH did a great job today shaving off next to nothing while modifying my Chinese indicator stand.

I have not yet used the new Bulgarian. Friday's purchase to utilise the so far unused corners on my collection of broken inserts.

The Lefty is a CTC. Half the price of the Bulgarians and three times the finish.

BT

[Michael G]

The triangular insert on the boring bar did a nice job initially on the toughish steel CTC use for their arbors but suffered from fine chatter when creeping up to the required finished size. Probably more to do with the bar extension and subsequent lack of rigidity than the insert.

Good point Bob - A friend of mine once told me that you only need one size boring bar for a lathe, but that is not 100% correct. While you might be able to get away with it, using the biggest boring bar you can with the shortest overhang will give the best finish. I now have 4 boring bars, ranging from one that will kick off from (I think) a 9mm starter hole to one that needs a 23mm starter hole. I also am much more particular these days about bar length - probably because I now have a set of tools next to the lathe kept there so I have no excuses about it being too hard to find the allen key...

Thats probably a worthwhile tip for someone new to metal turning in itself - have all the hand tools you need for changing tooling next to the lathe. Buy duplicates if necessary so you don't have to be put off because you can't find them in your main tool box and put them somewhere convenient so they are very accessible (don't leave them in that tacky tool box that came with the lathe) - a drawer directly under the lathe or a shadow board. You need to establish good habits/ routines with machines otherwise you will either do things in a less than optimum way or grow tolerant of slipshod (and possibly unsafe) practices.

Michael

[Ueee]

Hi Ewan,
if it is that magical finishing cut you are after, have you tried a HSS shear tool?
The finish is most acceptable :)
Here is a video that shows it.
Metal Turning with Contrary Tool.mpeg - YouTube (http://www.youtube.com/watch?v=hAF3Y5cR9z0)

Phil

Been meaning to reply to this for ages....
Good vid Phil, i have tried a few different shear tools on the lathe but never had success, but i have never ground one like that.
I got some WNMG 06T304 SF inserts in IC 907 last week, and took a few cuts. These inserts will leave a nice finish on the unknown bar i'm using to make collet chucks from (flavor of the month?) with a speed of 250 m/min (825 f/min) and a DOC from .1-.3mm, feed around .15mm/rev. The worst bit is the chips come off as continuous shavings.
I'm yet to put them to some free machining steel, 1020 or similar, i'm still waiting on grinding wheels so i can finish the collet chuck for the D/H and take the spindle off the lathe. Of course not much will happen now except a big re-arrange to make some space for the Blohm....

Cheers,
Ew

[19brendan81]

A collet chuck has been on my list of things to do for years now.....Where is the best spot to buy a D1-4 camlock blank?

re carbide - I bought some of those expensive high rake things from overseas. They are great when taking small cuts on ODs but I had absolutely no luck at all using them in my boring bar....they chattered, dug in, broke. Switched to HSS for boring and never looked back. The ones I bought (kennametal brand) were chrome like in finish and tended to break right through to the center hole when they let go meaning the whole insert was ruined, not just the tip. Dont think i'll buy more to replace the two I have left.

Besides that the only inserts I use are TCMT and DCMT inserts of varying brands. I find them to be tough and forgiving, they often come out when im doing stainless or cutting HSS. I find they will give a mirror finish on HSS and an excellent finish on stainless.

If im playing with mild steel I use HSS...I have really learnt to love the stuff after a rocky start.

[19brendan81]

Here are some photos of some of the Carbide tools that I use. The cheap set i have had for years, they are pretty spartan to say the least, but they work. Inserts are no name things bought from ebay. I mostly use these for roughing.

"Right" is my right hand turning tool (I think...cuts from right to left). Bought from CTC along with matching Iscar inserts. You can see damage on the tool holder where I crashed it once. I have a left one too, it is grey in colour...but couldnt find it last night.

Finish is just a quick shot of a cut I took last night with the RH tool pictured. 2000rpms, medium feed. I was playing with some HSS (that I now suspect to be a lesser grade of tool steel) and wasnt having much luck. Mounted the carbide tool, cranked the speed and got a nice finish first up....I am definitely a pro HSS guy....but you cant dispute the ease of using carbide. I just hate it how the chips come off burning hot.

Brendan

[Oldneweng]

Peppermint mostly. If I could get chocolate I would go that way with the occasional mix of the two.

Dean