# Lead Angle



## darkzero (Jun 7, 2009)

I'm looking to get another holder to use TNMG 331 AK inserts. Shank size needs to be 5/8" so I can have it milled to fit my AXA holders. My tools now have a 0° lead angle. I'd like to get something with a bit of negative lead angle so I can use one tool for turning & facing 
(or does it even matter?). I was looking for something in between 3-5° neg lead angle but all I can find is 15° neg lead angle. Is this way too much? What's the effect with a greater neg lead angle?

Only other option is to go with a holder with 5° neg lead angle using a CNMG 43_ insert. I only have an 8x14, wouldn't this size insert be overkill? I figure TNM_ would be a better choice for me because of the lack of power. Plus I'll get 6 cutting edges instead of 4. 
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## Mirage_Man (Jun 7, 2009)

When it comes to tooling there's going to be a ton of opinions as to what works best. I can only speak from my experience and according to the research I've done.. i.e. spoken with technical reps from Kennametal and Sandvik, a positive insert is the preferred tool for smaller machines. Heck, I have a 3HP machine now and I just ordered 2 more SCLCR/L holders in larger shanks and I.C. sizes. They use an 80 degree diamond insert. You can use CCMT or CCGT inserts in these holders. CCGT is what I use though for both ti and aluminum. The "G" in means that it has a ground chip-breaker as opposed to molded. Which means it's sharper. The sharper insert is more fragile but has worked really well for me and give a really nice finish. 

The SCLCR is used for both turning and facing. I would say the 21.51 size insert would work well for your machine. It has a 1/4" inscribed circle (I.C.) and is the size I started with on my Heavy 10. The last number tells you the corner radius of the insert. The higher the number the larger the radius. "1" is .016" corner radius. 

I will post a couple pics shortly.


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## Anglepoise (Jun 7, 2009)

Opinions vary as to the validity of using large negative tooling on 
light , underpowered machines. It works for some and there is no question
that money is saved with double the cutting edges when comparing positive to negative inserts.

I believe everyone on our sub forum would find the "Free" book put out by Sandvik called "Metalcutting Technical Guide" worth getting. It takes this very complex subject and explains it all with pictures and simple explanations on just what is happening at the cutting edge.

And for the record.........I am a 'positive' man......


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## Mirage_Man (Jun 7, 2009)

Here are a few pictures for you. Unfortunately I don't have any inserts for the larger holders yet. They should be on the way this week.

These first 2 pics show a 1/2" RH, a 5/8" LH and then a 3/4" RH. When I ordered the holders they were out of stock in the 5/8" RH holders so I got a 3/4" and milled it to fit my BXA holder.










This one is the 1/2" RH 21.51 insert in your actual holder. 





And here's that 3/4" milled holder.


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## precisionworks (Jun 7, 2009)

> the validity of using large negative tooling


I run more CNMG-4xx inserts than any other shape on my South Bend Light Ten (10-K), but it is a heavily built 10" machine, with excellent headstock support, and unworn ways. A 9" Atlas or Logan probably would not do as well.

FWIW, here's the totally nonscientific way that shape was chosen. An eBay search (under carbide insert) showed hundreds of CNMG-4xx inserts ... and a completed auctions search showed that most sold for a low price. I bought some inserts, got a toolholder, and gave it a try. It worked for me. Then a face mill was added, then boring bars, etc. They are a very tough to break shape, and almost all of mine wear out the "proper" way, which is flank wear. I can't remember ever chipping an edge.

There are other shapes in my inventory, and the 1/4" IC TMPT triangle is super handy when the job is small & there isn't room for larger tooling. The CNMG holder is huge by comparison.

Experiment with what's available, and don't buy much of any shape until you know it works for you.

EDIT: Just won an eBay auction for 5 Kenna inserts, CNMG432MP1 KC9240, $8.33 delivered


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## KowShak (Jun 7, 2009)

I use TNMG 1604xx / 33x inserts and have a few holders for them. I have a MTJNR and MTJNL, these are right and left hand turning / profiling tools. I also have a PTFNR holder this is used for facing. The tools I'm using are 25mm / 1" shank, which should give you some idea of the lathe I use them on.

Here are a couple of links that show those holders and what they can be used for, first the MTJNR (the MTJNR is the mirror image of this).

http://www.iscar.com/Ecat/familyHDR.asp/fnum/283/app/13/mapp/IS/GFSTYP/M/type/1/lang/EN

And secondly the PTFNR.

http://www.iscar.com/Ecat/familyHDR.asp/fnum/303/app/14/mapp/IS/GFSTYP/M/type/1/lang/WH

The first letter of the ISO / ANSI code indicates the clamping system, so you could for example use a *P*TJNR holder in place of the *M*TJNR holder, it is largely equivilent but uses a different clamping mechanism.

As has been mentioned, if your lathe isn't particularly heavy you might be better off with a positive rake tool, you can get positive / negative inserts to use in place of TNMG that give positive rake at the cutting edge, e.g. TNMS and TNMP inserts.

I'd agree with Precisionworks about the availability of CNMG inserts and holders, they are more common than TNMG, I don't see a lot of difference in cost between the two, but your experience may differ. CNMG have the advantage over TNMG that one PCLNR tool will turn and face where as you need two TNMG holders to do both operations, CNMG inserts are also tougher / stronger than TNMG too, although they only have 4 cutting corners rather than the 6 of TNMG. I quite like the idea of WNMG, but they're a bit new and aren't so common yet, they'll largely do what CNMG will (although they're closer to TNMG than CNMG for insert toughness / strength).

One of the users on here (wquiles) is / was using WNMG type inserts with a MWLNR holder, he detailed what he was doing in this thread.

http://candlepowerforums.com/vb/showpost.php?p=2528931


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## Anglepoise (Jun 7, 2009)

I think it also important to keep in mind the type of machining we do, 
If you are working on flashlights with a wall thickness of 25 thou, very sharp positive rake becomes almost a requirement. Also delicate parts like plastic and aluminum reflectors can be held very gently in the chuck if sharp positive rake tools are being used.


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## wquiles (Jun 7, 2009)

Yes, that was me, but now days I am running a positive CNMG 4xx tool:















Will


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## darkzero (Jun 7, 2009)

Thanks fellas. Great info here & is very helpful for me. Although I've learned alot just reading on the net the most valuable information I get from you guys here.

I do remember Brian saying positive inserts are most recommended for smaller, less powerful machines. Wish I had remembered that when buying my last two holders. BTW, thanks for the holders, they look great! :thumbsup:

I started off using the common generic 1/2" 5 piece indexable set using TCMT 31.51 inserts. I wanted to get something better now.

Here's what I currently use the most:











I picked up MTGNR & MTJNR 08 2A holders. These use 1/4" IC inserts & have a 7° neg rake. The MTGN has a 0° lead angle so I got the MTJN for facing. I had these in mind cause the TNMG would give me 6 cutting sides & that would be more economical.

Didn't realize there wasn't a very good selection of inserts available for TNMG 1/4" IC. I started off with a Seco TNMG 222 MF1. Didn't like how they cut too much because of the larger corner radius. Then I got a Valenite 221 F1 & Valenite 222 F3 to try. The Valenite 221 with fine chip breaker does ok with alumn but I only get a nice finish when using lots of cutting fluid & when facing some drill rod, towards the center the finish was poor as if there was chatter? The Valenite 222 F3 has a higher positive angle so I thought it might work better. A little bit better but not all that much. I don't like the larger corner radius. I was planning on getting a TNMP 221 to try but I don't think I will now.

First thing I noticed was the TNMG inserts being negative they didn't feel as sharp as the TCMT inserts. I also noticed that the TCMT uncoated carbide seems to work better with alumn over the Tin coated carbide. With the coated TNMG inserts I seem to get alot of BUEing (is that the correct word?).

Based on the information you guys have given me I'm going to go back to using positive inserts & I'd like to stick with the 3/8" IC size & no larger. I'd like to get something with a bit of a neg lead angle so I can use the same holder for turning & facing. With the 0° lead angle I have now on the MTGNR & AR they're ok when turning a 90° shoulder but it just doesn't feel right to me using them for facing as the entire side of the edge is touching the workpiece. I know I can always turn the tool post when facing but I want to avoid having to make any unecesary adjustments during the job.

I'll be working mostly with alumn, brass & copper so I want to find an insert that will work best for me. The inserts I was looking at are H01 with an AK chip breaker & mirror face. They also have the inserts available in CC & TC shape. I've been planning on sticking with the triangle shape since I have a smaller machine plus I'll get three cutting edges. Looks like my choice now is to either get a STJCR/L which have a 3° neg lead angle & use 32.5 inserts but I will have to get them milled to fit my holder. Or get SCLCR/L which have 5° neg lead angle & use 3/8" IC inserts but I won't have to mill them to fit. I'm leaning toward the SCLC 08 3As, oh well, I 'll have to live with just two cutting sides per insert. 

I just thought the 80° diamond shape might not work as well for my little maching but my boring bars use CCMT inserts & they seem to work rather well. In the mean time I'm going to go back to my generic 1/2" holders with uncoated carbide as I wait for my new holder & inserts to come. I'll be throwing the Dorian MTGNR & MTJNR 08 2A holders with inserts on ebay unless anyone here might want them. If yes send me a PM or email.

Anymore advice or recommendations is well appreciated! Sorry for asking all the stupid questions but I'm eager to learn & I'm not afraid to ask so please bare with me as I learn.  I feel more comfortable asking you guys here rather than on the machining forums. Thanks again. :twothumbs


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## KowShak (Jun 8, 2009)

darkzero said:


> I picked up MTGNR & MTJNR 08 2A holders. These use 1/4" IC inserts & have a 7° neg rake. The MTGN has a 0° lead angle so I got the MTJN for facing. I had these in mind cause the TNMG would give me 6 cutting sides & that would be more economical.
> 
> Didn't realize there wasn't a very good selection of inserts available for TNMG 1/4" IC. I started off with a Seco TNMG 222 MF1. Didn't like how they cut too much because of the larger corner radius. Then I got a Valenite 221 F1 & Valenite 222 F3 to try. The Valenite 221 with fine chip breaker does ok with alumn but I only get a nice finish when using lots of cutting fluid & when facing some drill rod, towards the center the finish was poor as if there was chatter? The Valenite 222 F3 has a higher positive angle so I thought it might work better. A little bit better but not all that much. I don't like the larger corner radius. I was planning on getting a TNMP 221 to try but I don't think I will now.
> 
> ...



Neither or MT*G*NR or MT*J*NR should be used for facing, the correct holder for facing should be MT*F*NR if such a holder exists or PT*F*NR if it doesn't, its the 'F' in the middle of the code that's important here.

If you're moving to positive rake tooling and sticking with triangular inserts the equivilent to the three holders I've mentioned would be something like ST*G*CR, ST*J*CR and ST*F*CR,,, 

The ISO / ANSI codes describing the tool holders are a little scary at first sight but they're pretty simple e,g,

'S' at the start of the code denotes the insert is clamped by a screw, (M indicates a pin and clamp clamping system).
'T' indicates a triangular insert (C would indicate 80 degree diamond)
'F' indicates the orientation of the insert
'C' indicates the rake angle, 'C' is positive 7 degree (N is 0 degree)
'R' indicates the tool is a right handed tool.

All you need is a good guide to decode them

http://www.carbidedepot.com/formulas-th-d.htm

As I've said, you can get an insert for a triangular negative rake toolholder that has positive rake, e.g. TNM*P* or TNM*S* but you may be better off going for TCMT or CCMT type inserts, CCMT are pretty common and that's what my boring bars all use.


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