Insert Lathe Tooling - an education?

[BadDog]

Reading another post, I saw some interesting stuff on insert holders from Jose, Harold and others. I still plan to use HSS for much of the work on my new lathe (17x60 for those that don't know), and just tonight made some "packing" bars to allow me to continue to use my favorite/prized MoMax and Rex bits (some 1/4", mostly 5/16, and some 3/8) in the large CXA holders.

But, with 7.5hp on tap and 6000 lbs of rigidity, I plan to execute a foray into the land of carbide inserts. On my previous lathe (11x37 Rockwell) insert tooling was pretty limited and used only for nasty stuff like mill scale, rust, and cast iron. Not much to say, I had to look for positive tooling exclusively as negative was largely out of the question with only 1hp. And holders had to be small or milled down. No big deal. But of course, the new lathe opens up new options by the bucket load.

To start with, I picked up some cheap/free negative rake triangle insert holders in various configs suitable for roughing, turning to shoulder, and facing (it'll be nice to double the cutting edges!). That covers the main bases and uses the cheapest of the insert styles, easily available in ground or molded with semi-exotic chip breakers and such. I've also got some 50 or so TPG-322 and 321 ground (obviously) and uncoated inserts, so I got a basic holder set for those, and they'll do lovely for finish work.

My mentor told me his favorite insert for general use on his Mori 1250 is the 80* diamond with molded inserts. He even gave me a holder for facing and turning to shoulder along with a selection of different style inserts. Did I mention he's a great guy? I also got a like new 1" x 12" Kennametal boring bar that takes the same insert for $40.

Finally, I have been using Sandvik cut-off tooling (151.2-21-25, 151.2-21-30 and 151.2-25-40 depending on depth and kerf) even on the Rockwell, so I'll continue to use these.

Question is, my education in insert tooling is VERY limited. Previously I only focused on that minimal subset suitable for the Rockwell, and without much interest in that. Harold mentioned "RB" type in particular. No clue what that is, or why I would care? I also know there is a new(ish) nomenclature that is often used and provides for "more sophisticated" inserts (at inflated prices of course).

So, all that said (for background), what are the things I REALLY need to know, and what (specifically) do I need in my arsenal. Particularly things I might not notice or think about due to my ignorance.

I do know a bit about such issues as carbide being very sensitive to minimal DOC (more for molded than ground), and the "C" grading system (new one confuses me).

Specific goals:

1) Roughing "mystery metal". Rusty steel, mill scale, interrupted cuts.
2) Finishing "mild steel" (soft, low carbon, 1010-1020, etc) to a very fine finish. In my experience, hard to do even with sharp HSS, almost impossible with carbide.
3) I work mostly with steel, but often use aluminum too. Same needs, roughing and finishing that utilize the new lathe capabilities, but also retain a good cost/benefit ratio.

Thanks in advance for any thoughts you care to provide. Obviously I've got a lot of searching and reading, but seeing that "RB" reference along with some others prompted me to start this thread.

[Bill_Cook]

The MSC catalog covers indexable tooling extensively starting on page 633.

The info is good, but the prices aren't.

BC

[Harold_V]

Harold mentioned "RB" type in particular. No clue what that is, or why I would care?

You might be interested because of their incredible ability to provide excellent finishes.

Do bear in mind that I am woefully behind in current technology. It's entirely possible that there are inserts on the market today that would yield better results. I've included a picture of the inserts. Take note of the outstanding finish of the grind. Unlike many carbide inserts, they are fully diamond ground and have a small tip radius so they are very good for fine finishing.

what (specifically) do I need in my arsenal. Particularly things I might not notice or think about due to my ignorance.

Because my background is limited to small production and tooling, I have never had need for extensive tooling. What has served me particularly well is a TNMG-322 insert. They are likely one of the least expensive inserts on the market, and do an excellent job of roughing. For your lathe, you'd likely need to move up to a 422 insert instead, although if the work you do tends to be on the smaller side, the 322 could serve you exceedingly well.

TNMG inserts are available in a variety of grades and tip radii. They come with, or without, molded chip breakers. It is the one insert that I would not be without. YMMV, due in part to the monumental changes in carbide technology since my years in the shop.

I'm a victim of my times, but I am still well served by my choices. I have no doubt, there are likely better choices to be made. I wouldn't know one if it presented itself to me.

I know a bit about such issues as carbide being very sensitive to minimal DOC (more for molded than ground)

That's true in general. Negative inserts do not make good finishing tools, but on a large machine, taking a reasonable depth of cut, and at recommended surface speeds, they can yield nice, but coarse, finishes. One place I observed that very thing was with the final drive shafts for the Eimco crawler tractor that were being machined on a large American tracer lathe (right behind the 17" Axelson I ran). Excellent surface finish (mirror, with no tearing), but coarse, as I said.

You'd find the RB insert very good for light cuts, although there are few tools that will deal with mild steel and yield a decent finish. It might address your goal for your line item 2)

1) Roughing "mystery metal". Rusty steel, mill scale, interrupted cuts.
3) I work mostly with steel, but often use aluminum too. Same needs, roughing and finishing that utilize the new lathe capabilities, but also retain a good cost/benefit ratio.

Again, a TNMG can serve in that capacity. The C2 grade (883 Carboloy equivalent) is excellent for cast iron, aluminum and stainless. My choice includes inserts with breakers. I don't like stringy stainless chips, for obvious reasons. Cast iron can be machined with satisfaction without the breaker. I'd stick with a C5 (Carboloy grade 370) for ferrous alloys, except for stainless.

Someone like Kap may well be the best source of information. He has remained in the shop and has extensive experience. Along with Kap, there are others on the forum that have current commercial experience and may be able to address the latest in carbides. It would prove to be a good learning experience for me as well.

Harold

[BadDog]

Thanks for the information.

Now that I know what an "RB" is, I've seen them before. Looks kinda like the predecessor the high priced "tri-gon", but with more interesting chip breaker. I've also got some triangular and some 80* inserts with some slick looking little flutes and dead sharp positive rake edges. No idea what they are called and haven't tried them yet.

Oh, and the "why I would care" wasn't intended as a slight (doubt you took it that way, just looked funny when I read it in your quote), but rather to expose the depths of my complete ignorance of the form.

And good point on the catalog Bill. I've largely grown to ignore it (and some others) due to price relative to identical tooling from Enco. Seems I'll have to dust it off again (and perhaps some others too).

[Harold_V]

Oh, and the "why I would care" wasn't intended as a slight (doubt you took it that way,

Correct. You, above almost all others, have been open to information. I expect you needed to be enlightened. Reminds me of the night I suggested you abandon carbide and start using HSS. I've never experienced anyone responding as positively as you did. I commend you for your attitude.

Harold

[BadDog]

Thanks, and I remember that day too. That and other advice from you many others has made me much more successful at my little projects. And the impact was so large that I find myself almost reluctant to go back to insert tooling again, even though I now have a lathe that can capitalize on it. In fact, night before last I spent a while making some "packing" for my CXA tool holders so that I could get my old HSS bits (mostly 1/4", 5/16", and 3/8") into my CXA 3/4" holder slots (and on center). Just some pieces of 1/2" plate drops from another project, and they were perfect for "packing" with only minimal cleanup (fly-cut to square and remove mill scale, then a notch with EM to fit the bit with a back stop). No reason they won't work just as well now as they did then, I just have more options now (like negative rake inserts). And I'm sure not throwing out my horded collection of MoMax and Rex bits in dozens (and dozens) of different grinds!

As for the rest, I try to see and acknowledge my ignorance as well as my weaknesses. One so I can correct (or at least improve) it, the other so I can work to neutralize it as much as possible. It's a purely selfish motivation. I learned long ago that I would progress further and faster by keeping my mind opening and trying to learn from others with much more experience. But it's often hard to avoid the trap of getting defensive over (and then defending) the opinions we form when we think (assume) we have good evidence to form those opinions.

In any case, thank you for the kind words and for what has proved to be very good advice and taking the time to offer it. You and other fine folks have certainly changed my experiences for the better. And fortunately for me, continue to do so...

[Harold_V]

The one bit of advice I can offer now that you have a larger machine is to increase the size of your HSS blanks. Even with my 12" machine, I stick with ½" in most cases. I do have smaller tools, but they tend to be used for light duty functions. It takes more time to grind the larger sizes, but they perform much better, offering the required rigidity and heat carrying capacity when called upon to serve under heavy conditions.

For light cuts in non-ferrous---makes little difference.

Harold

[BadDog]

Yes, I understand that and I'm already keeping eyes open for some larger HSS blanks. I already have a few 1/2 blanks, but generally avoided them as not necessary for my old lathe and taking too long to grind (or to change grinds on), and saves money in the bargain!. Basically, they were only for use in my larger fly cutters.

Main reason for the "packing" blocks was to use what I have on hand (a fairly large volume now) and already familiar with. Eases the transition and these are perfectly fine for the vast majority of what I use HSS on. That is, the large lathe itself is really not necessary for most of what I do, and the Rockwell could handle most of it easily enough. So, my theory is that same tooling that worked on the Rockwell should be fine for that (again, at least during transition). And of course, I'll be experimenting more with carbide as well as larger HSS tooling as I find inexpensive deals. So much to learn, so many toys to buy, so little life left...

[GlennW]

If rigidity is what you are after, this is the right way to go from Aloris. Uses CNMG inserts which are very common and inexpensive as compared to some others.

Glenn

[GlennW]

I guess while I'm signed in...

The up turned, sharp edge, polished carbide inserts work exceptionally well on aluminum and brass/bronze. Can't recall chipping any either as they are quite durable for positive inserts. Even use them ocasionally for finishing SS and mild steel.

Probably similar infunction to the BG's.

These don't appear to be as highly polished as the ones I use, but similar.

Glenn

[Mark Hockett]

Baddog,
We have fairly similar lathes with the same HP. This is what works for me, My lathe is CNC and used daily in a production environment, but this has also worked for me on a manual lathe of the same size. All of my rough facing and OD turning is done with CNMG 432 or WNMG 432 inserts on a negative rake holder. These inserts have a .031 radius on the nose. I use inserts similar to the ones Glenn uses for aluminum and Tungaloy TiALN coated inserts for steel and stainless steel. The TiALN inserts are nice because you don't need to use coolant with them. The CNMG and WNMG inserts are good for roughing due to the fact that they are very robust and can take some heavy cuts but they are not good for finishing because the insert does not have much front cutting edge angle, usually about 5 deg. The problem with them for finishing is the way the chip breaker works. Many times the chip will get caught between work and the insert, due to the lack of front cutting edge angle, and cause an unsatisfactory finish. I use around 400 SFPM for cutting steels like 12L14 and 1144 stress proof, 300 SFPM for roughing 4130 and 4140 and 900+ SFPM for aluminum. I only use coolant on aluminum. For feed rates on roughing I use from .010" to .016", my lathe has a load meter so I crank up the feed rate and depth of cut until it hits 100%-110%. For finishing I use DNMG 431 or VNMG 431 inserts on a negative rake holder. These inserts are 55 deg and 35 deg so there is more front cutting edge angle and it is much more difficult for stray chips to get caught between the work and insert. This is one of the reasons the cutters are mounted upside down on CNC turning centers, the chip falls away from the insert. You will also notice I finish with a .015" nose radius. The smaller nose radius for finishing helps maintain enough chip load during lighter cuts. When using carbide tooling chip load is very important for a good surface finish. I finish using a .010" to .020" depth of cut and .006" to .010" feed depending on my customers specifications for surface finish. With a .006" feed and the .015" nose radius you need a magnifying glass to see the lines on the surface. I also raise the SFPM for finishing to 1000 for free machining steels, 800 for 4130 and 4140 and 1200+ for aluminum. By raising the SFPM for finishing it also helps maintain enough chip load to get a good surface finish with the lighter cut.

[GlennW]

Hello Mark,

Good info, thank you!!

Have you tried any Cermets?

Pretty impressive little felllas.

Glenn