Carbide Conundrum...

[AdeV]

...having broken the only two carbide inserts I have (came with the lathe), it's time to buy some new ones. I have three indexable holders in all, so I'll buy a set of 10 inserts for each.

Considering the low volumes, where in the UK (or from Forrin if it's cheaper including postage) am I best buying them from ? I need a set of triangular, a set of square, and a set of 80 degree rhombic inserts.

TIA!

[bogstandard]

Ade,

I am not being awkward, but could you tell me what angle the rain came down at when it last rained in your area?

Selecting and buying inserts isn't quite as easy as you think, and if you think the question above was unanswereable, then the question you have just asked comes into the same category.

Buying inserts is an absolute minefield, and if you can't get within the ballpark with sizes and reference numbers, you will struggle to get an answer.

I think Darren has his finger on the pulse in that department, but without a little more info, even he will struggle.


Bogs

[AdeV]

I am not being awkward, but could you tell me what angle the rain came down at when it last rained in your area?

- easy: 90 degrees from the horizontal (dead straight down), between 9pm and 9:50pm, last night. No, not joking either....
(edit: I should point out, I only know this because I had to go out in it, about 4 times. And it was VERY wet. You probably had the same rain a little later on)

I should perhaps have been more specific. The inserts I'm after are:

TPMR 1603xx
SPMR 1203xx
CNMG 1204xx

In all cases, xx = 04, 08 or 12 and represents the radius (see followup question).

I think I'd like to go for a moderately hard grade (say, P10 thru P30), particularly as I will tend to be machining on the slow side.

With regard to the radius, please correct me if I'm talking cack - but the 04 (smallest radius) is good for hogging off metal, but will leave a rougher finish. 12 (largest) will leave a nice surface but can't cut so much metal, and 08 would be somewhere in between? If that's basically correct, then I should be getting either the 08 or 12; I'm happy to spend longer at the machine to acheive a nice result, rather than racing to get the metal off & ending up with a poor surface.

[Darren]

John's Right ... I have spent a long time and many hours studying inserts and still know just about sod all in the scheme of the insert world.

One thing I do know is that you shouldn't pay too much interest in getting the right type. I'm talking of using alloy inserts for steel and vice versa. Both will do each others jobs in our little world. We could also be talking cast iron, hard grade steels, etc, etc. They will all work for us.

Where it really makes a difference is in the production world. The right tip might make an extra part or two (or 50) and cut the speed of each part down by 30 seconds. This is all important on a £100K CNC machine with an operator on £35K a year.

But for our needs it means very little .... so hunt the cheapest, that's what I do.

Take for example that tough Nickel Steel I've working with recently, I'm pretty sure on the first part I used tips for cast iron and it came out ok.
A CNC machinist I used to chat with swears by alloy insets for steel ... don't last as long but he reckoned it gave a better finish.


With that out of the way you need some shapes and sizes.

Some charts will help ....... http://www.carbidedepot.com/formulas-insert-d.htm

Come back with some data that you do know for the tips and lets see what we can find.....  

[Darren]

OK, crossed post ...

You say you have had some trouble machining steel, weren't using those triangle tips were you by any chance ... ?

[AdeV]

OK, crossed post ...

You say you have had some trouble machining steel, weren't using those triangle tips were you by any chance ... ?

I used the triangle tip until it broke (translation: until I broke it...). The rhomboid tip already had one knackered index, I was using the 2nd index when I accidentally bumped it into the shaft I did yesterday, which was turning very slowly. Snap! End of insert. The square holder never had an insert in it.

In fact, every time I've bust a tip, it's because I've accidentally rammed the workpiece with the cutter. I do hope to be doing that a lot less as time goes on (never again would be good!)

But.... do share: Is the triangle unsuitable for steel? I've not (yet!) found any wisdom in Machinery's Handbook about cutter shape vs. material...

What are your thoughts on the radius question? 

[Darren]

Sorry I'm mixing them up I meant the rhomboid CNMG not the triangle.

Note the second letter, this indicates no relief angle, usually reserved for double sided inserts. Because there is no relief angle you need the tool bang on centre. You might get away with a touch low, but certainly not high, even a nats wotsit too high and you'll be in trouble.

I believe they are intended for larger powerful machines with higher removal rates and don't really suit us types.

Try CCMT or CCGT in that order.

As for nose radius I doubt you'd notice the difference .... let us know if you do ....

Carbide don't like sudden heavy loads as you have found out   Even a stall or a belt slip will take the end right off .... it can get expensive if you are a bit clumsy.

If you want to cut something irregular like hex or square, use HSS till it's been made round  

[Trion]

You say you have had some trouble machining steel, weren't using those triangle tips were you by any chance ... ?

Just curious, as I'm about to buy my first indexable lathe tools. Are you saying triangle inserts like TNMG aren't any good? I have looked at several tool holders, and concluded with MTJNR-L beeing very versatile, and each insert has 6 cutting edges. Grizzly even sells a 3/4" boring bar using TNMG inserts.

AdeV: I find ebay is actually a good place to look for inserts. The way I do it, is to search for the insert type I'm after, find a reasonably priced set from one of the big manufacturers and check the exact grade and chipbreaker specifications using the look-up options on carbidedepot.

Insert grades:
http://carbidedepot.com/grade-info-nw.asp

Insert chipbreaker:
http://carbidedepot.com/chipformer-info.asp

[Darren]

I'm not saying xNxx tips are no good, just that you might have trouble using them on smaller machines.

My lathe is considered small by the tip manufactures.
I have found it hard to get good results, not impossible, just hard sometimes, enough to give up on occasions and use something else instead.

Never had any issues with a xCxx tip  

[AdeV]

Sorry I'm mixing them up I meant the rhomboid CNMG not the triangle.

Note the second letter, this indicates no relief angle, usually reserved for double sided inserts. Because there is no relief angle you need the tool bang on centre. You might get away with a touch low, but certainly not high, even a nats wotsit too high and you'll be in trouble.

Yeah, I think I am (or, rather, was) running it a gnat's high. Which, now I've read up on insert codes & rake/relief angles, makes sense. I've been doing that all afternoon instead of working, oops.

I believe they are intended for larger powerful machines with higher removal rates and don't really suit us types.

Try CCMT or CCGT in that order.

As for nose radius I doubt you'd notice the difference .... let us know if you do ....

Wilco, ta. If the difference in nose radius is that small, I've no chance of spotting it  I presume that the tapered hole (the "T" in the code; and I know it's not T for Taper, that's just a happy coincidence) won't be a problem with the mounting scheme I've got? It's got a sort of pin arrangement which pulls the insert back into the holder (tool code is PCLNR 2525M12), the insert that's in it is a straight hole type ("G"), but no-one makes a CCMG or CCGG; or even a CCMM or CCGM, because I assume that with a relief angle the insert gets a distinct "top" & "bottom".

Am I making this too hard for myself? Should I just buy the cheapest CCxx with a hole in?

Carbide don't like sudden heavy loads as you have found out  Even a stall or a belt slip will take the end right off .... it can get expensive if you are a bit clumsy.

If you want to cut something irregular like hex or square, use HSS till it's been made round 

I'd always planned to go HSS pretty well exclusively; but these three holders were sat there... if I was buying new tool bits, I'd get HSS for the lower price & easier understandability; but if I can tool up these three holders with 10x bits each for less than 60 quid (which seems achievable), then I may as well. 

Tion - I've been using eBay for the codes, but I got a bit bogged down in the grades. However, I'm now pretty well ignoring the grade & just looking at the prices...

I found this tool selector: http://www.canelatools.com/cataleg/tec2/tec-ins-index.htm

which seems pretty good (and quite interactive); doesn't cover the chip breakers or grades though.

[Darren]

Just looked up your toolholder http://www.iscar.com/Ecat/familyHDR.asp/fnum/291/app/20/mapp/IS/GFSTYP/M/type/1/lang/EN

It's designed for neg rake with the angle it holds the tip .... so it might be wise to stick with those for this holder.


If I were in your shoes, I'd prob buy a new toolholder that takes what the rest of us use ..... and easy to find cheap tips.
Come back to you current tool later ... You can't have too many tools anyway 

SCLCR    http://www.rdgtools.co.uk/acatalog/TURNING_TOOL__SCLCR_.html

[bogstandard]

Ade,

I invested in a good quality complete set like the ones Darren has shown, that all use the same tip, a CCMT 060204. You can buy these tips very cheaply and do last rather well. They have two cutting angles, and if you bought the full set of tools, both sets of angles are used, so when the pointy ones go dull, you save them for use on the other toolholder that uses the not so pointy cutting tip. They are not finished with when all four tips are worn, as they are then used in the chamfering tools, where you get to use all the cutting faces. You can really get your monies worth out of those tips, not one part is wasted.

I bought the 16mm set for my machine, and they have turned out to be one of the best tooling investments I have made. I did the same with my previous lathe, only they were 12mm. A bit pricey initially, but well worth it in the long run.

http://www.chronos.ltd.uk/acatalog/Glanze_Boxed_Sets_of_CCMT_Turning_Tools.html

To get an idea of what they are used for and how the tips are utilised, click on the picture of any of the bottom four sets. The 16mm one is the best quality to look at.

John

[AdeV]

My brain now hurts...

John, that looks like a nice set of tooling; and the price ain't too bad either. Should be within reach of the Xmas money... Thanks for the link.

Darren, does that mean using the CNMG insert?

Tomorrow I'm going to my local 2nd hand toolshop. Maybe I'll find some nice chunky HSS bits to play with.... 

[Darren]

Adev,

I think with that toolholder you will have to stick with the CNMG inserts. If you put a CCMT in it the geometry will be all wrong.

But as I said before, the zero relief inserts are a bugger and you'd be best leaving them alone for now. Maybe come back to them later. It's just an opinion of course, you may care to take your own route.

If you try CMMT you'll be amazed at the difference on our smaller machines.

[Trion]

I new to this, so I might need it in with a teaspoon.. Are zero relief inserts still not good, even when used on tool holders with an angled face for the tip?

That Glanze set sure looks good!
Btw. found the 12mm glanze set on grizzly's site, they have a sharper image of the tool holders
http://www.grizzly.com/products/Glanze-Turning-Tool-Set-12mm/H5681

[Darren]

Trion,

I believe it has something to do with the cutting angle. Imagine a zero rake cutting edge angle, (between the top face and the leading face) lets call this 90 degrees.

Now take a cutter with a 7 deg relief, that makes the cutting edge 83 degrees.

Which would you rather try to cut a piece of steel with, a sharp tool or a blunt one? Now think about what our underpowered lathes would prefer.

(these are not the true angles I'm just simplifying it as the top edge will have it's own angles)

So why have zero rake tips at all?
I'd imagine they would have a stronger cutting edge that would last a lot longer and take more heat/pressure/punishment in a production environment. I don't know how much HP a modern production lathe would have, but lets say 25HP is going to have no trouble pushing this blunt tool into the work to be able to get a decent cut going. They also don't take that final finishing skim that we tend to do. They just cut it right first time around as time is money .....

[AdeV]

Darren, that's a nice explanation - as in, it makes sense to me, and if it does that it must be clear!   

I think I'll save my money & get that Glanze set.

[Trion]

Thanks for the thurough explaination, makes perfect sense when you put it that way.
I'm guessing there will be a glanze set heading my way aswell

[Darren]

These are only assumptions from the info I have managed to glean so far .............

I could be completely wrong ..... It's not unheard of ..... 

[Darren]

A large
nose radius provides a strong edge, capable
and dependent upon high feeds for
proper cutting edge engagement. The
small nose radius means a weaker point
but one capable of fine cuts.

http://www2.coromant.sandvik.com/coromant/catalogue2007/tech_a.pdf

[AdeV]

A large nose radius provides a strong edge, capable and dependent upon high feeds for proper cutting edge engagement. The small nose radius means a weaker point but one capable of fine cuts.

Blimey - the complete opposite of HSS, then. Good find Darren, thanks for that!   

[kvom]

My only experience to-date with carbide for turning was on the CNC lathe during class.  What we learned was that a typical relief angle between the work and the insert is about 7 degrees.  Since the orientation of the insert is fixed on a CNC tool carousel, you need separate inserts for turning and facing.  For facing we used the 80 degree inserts so that there was some "meat" behind the nose.  For turning we used the 50 degree inserts.  I broke a couple of the the 50 degree ones trying to take heavy facing cuts before the difference was pointed out to me.   

The size of the nose radius determines how small a transition you can make when turning a taper or a shoulder.  I think all the inserts we used on the CNC lathe were .032.

I have a RH turning tool with inserts on order, so I will get some experience with manual turning soon.

[Darren]

Blimey - the complete opposite of HSS, then. Good find Darren, thanks for that!  

Probably because you increase the rpm with inserts (or they don't work properly) around 2-3 times that which you would use for HSS.

You can feed it faster too ....  

I mentioned elsewhere that that tough steel I've been using would eat HSS in a flash, but it needs 2,500 rpm on a 16mm diameter to cut properly.
You would make a right mess of HSS tooling in this scenario.

On my other lathe I would turn brass at 3,000 rpm to get a nice hand feed finish.

[AdeV]

My lathe's top speed is 670rpm 

I'll just have to cut stuff that's at least a foot in diameter, to bring the SFM speed up 

Where's the smiley for "enormous crash as massive lump of spinning metal carves its way out of the workshop"? Oh, here it is:

[Darren]

My lathe's top speed is 670rpm 

Ah ..... not quite sure what to say ....

Erm, that does seem slow .. what's your lathe again? Has someone altered the drive, what type of bearings does the headstock use?