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?

[AdeV]

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?

It's a 1930's design Edgwick, and gives speeds between 17rpm and 670rpm...

The headstock shafts are on ball races & the spindle is on taper roller bearings, according to lathes.co.uk

The Mk2 range offers the same spindle speeds, and suggests that with a faster motor will go up to 1000rpm; I dare say with a 2-speed motor I could push it as hard as 1200rpm; but tbh, it sounds quite fast enough doing 670....

[Darren]

I think you are going to struggle with tipped tooling of the insert type with smaller diameters as they are not sharp like HSS. This is why they need to be worked, ie higher speeds and feed rates.

TBH I'm not sure what to advise, I've done hardly any lower speed turning. Maybe brazed tungsten tip tooling would be more suitable for you as you can hone the edge on those to a razor sharp edge with the right stone on the grinder.

Perhaps Bogs or someone else could advise here ...?

[ksouers]

Ade,
There is another possibility...

There is a company here in the US that makes insert tools out of HSS.

http://www.arwarnerco.com/index.html

You might be able to find a local vendor that carries them.


Kevin

[AdeV]

Kevin - that looks like a really interesting set. LMS seem to sell a selection of HSS inserts, no sign of any in the UK; but I will keep looking. Thanks for the link  

Darren - no problem, you are probably right. The only reason I was really interested in inserts is because I have these three holders, it seemed a shame not to use them. Especially the rhomboid one, as that's the one I can get closest to centre height with relative ease. Until John pointed out that Glanze toolset, I hadn't planned on buying any more holders. Now that my top speed is an issue, I'll probably steer clear & stick to HSS. If I can get any of those inserts that Kevin spotted for reasonable money. which happen to fit my holders, then I'll go down that route rather than carbide.

I'd hoped to have time to buy some tooling this morning, but didn't; so I'll be going tomorrow morning instead.

Hopefully, I'll be able to make my QCTP soon, which will solve the biggest problem I have with regular HSS tools (centering the cutting edge).

[75Plus]

Hopefully, I'll be able to make my QCTP soon, which will solve the biggest problem I have with regular HSS tools (centering the cutting edge).

This is the way I solved the tool height problem. I milled a slot in a piece of aluminum to a depth that would put the tool bit on the center line of the work piece. One piece can locate two different sizes of bits. I like to use smaller sized tools for small work pieces. I even made one with a 7 degree slope to use tool bits that had been ground for use in the old Atlas holders.

[ksouers]

Kevin - that looks like a really interesting set. LMS seem to sell a selection of HSS inserts, no sign of any in the UK; but I will keep looking. Thanks for the link  

You're welcome.

Might want to send A R Warner an email to see if they have a UK, or at least an EU, vendor. If not I'm planning to place an order with LMS after the holidays, I can have a couple extra put in the order and I'll drop them in the post for you.


Kevin

[AdeV]

Kevin - that looks like a really interesting set. LMS seem to sell a selection of HSS inserts, no sign of any in the UK; but I will keep looking. Thanks for the link  

You're welcome.

Might want to send A R Warner an email to see if they have a UK, or at least an EU, vendor. If not I'm planning to place an order with LMS after the holidays, I can have a couple extra put in the order and I'll drop them in the post for you.

Kevin - that's a good idea; and many thanks for your kind offer. If I don't succeed in finding a UK seller, I'd definitely be interested in taking you up on that one.

[Darren]

Ade, No dis-respect to Kevin I really can't see the point in using HSS inserts  Might as well use regular HSS blanks.


I think you would be much better off using these http://www.iscar.com/Ecat/familyhdr.asp/fnum/919/app/105/mapp/IS/GFSTYP/M/lang/EN/type/1/cat/3602210/relation/TI/tool/I

OK so they are meant for alloy turning. But I'd bet that though not designed for steel they will last a whole lot longer than HSS inserts.

I'll let you know as I've just bought a load for myself ............. too cheap to leave behind ... nobody wants them.

The are 09 size, but you can find 06 easily enough.

http://cgi.ebay.co.uk/CCGT-09T304-AS-IC20-ISCAR-10-inserts_W0QQitemZ260522934017QQcmdZViewItemQQptZUK_Home_Garden_PowerTools_SM?hash=item3ca8607f01

[jgroom]

I think it would be pretty slick.  You gain the advantages of inserts, i.e. no grinding, just spin to a new point when dull, without the big disadvantage, the edge chipping when the belt slips, motor stalls, you look at it wrong, or it just feels like it.  Unfortunately it looks like the price is the same as carbide  , sooo.......  I guess I'll keep practicing my grinding.

Jeff

[Darren]

I think it would be pretty slick.  You gain the advantages of inserts, i.e. no grinding, just spin to a new point when dull, without the big disadvantage, the edge chipping when the belt slips, motor stalls, you look at it wrong, or it just feels like it.  Unfortunately it looks like the price is the same as carbide  , sooo.......  I guess I'll keep practicing my grinding.

Jeff

If you are having undue problems with chipping then it may be that you are selecting the wrong grades for the job in hand? Or even shapes.

Take for example a common Sandvik CMMT 06 02 08-UR 235 P45 tip,

We have already discussed shapes further up with CMMT being quite versatile having two different angles for us to make good use of. One being stronger than the other.

The No's relate to size, thickness and corner radius. But what about the letters at the end? xxxx xx xx xx-UR ? Anyone take any notice of these?

Well the R stands for Roughing, (they will also finish fine as well in my exp) This gives us an indication of how tough a tip may be. You will also find F=fine and M=medium

Then we have 245. This relates to the specification of the makeup of the tip in more detail. In this case 235 is an extremely tough grade with a three-layer coating of TiN, TiC and TiN. The total thickness is only 3 micrometer. GC235 is an exceptionally good grade for intermittent machining, the machining of stainless and carbon steels at low speeds and parting operations.' - 'For toughness demanding operations in steel and steel castings. Suitable for low speeds and unfavourable conditions. Extremely good edge security.

Considering this grade is also suitable for low speeds then it may be a good choice for some of us with older machinery.

Lastly there is P45, This relates to P=Steel of a hardness of 45, which is pretty hard.

As I have said before we can use most types of different tips for most of our machining. But if you are experiencing excessive chipping or a limited top speed, then a tougher tip as described here may be a good choice for you.

[AdeV]

If the P45 matches the P-values in Machinery's Handbook, then it's a very resilient cutter which is ideal for nasty metal & interrupted cuts, but will be subject to wear. So it's strong rather than hard, if you see what I mean.

[Darren]

Yes, I was referring to the metal being hard not the cutter  

[jgroom]

Hi Darren.  The main problem I have is the leather belt on my 9" South Bend.  If I take a big enough cut to make the cutter happy it tends to slip occasionally.  Of course it doesn't help that my indexable set is from Horrible Freight (and worth every penny  ) and shop funds don't allow a big outlay for good inserts at the moment.  I have a few brazed carbide tools that work ok for (careful) hogging, but I get a much better finish with HSS.

I plan on updating the drive to Poly V-Belt (Hot-Rodding a 9" South Bend Lathe, HSM, July/Aug 2006) which should take care of the slipping problem.   Hmmmm... looks like it's -12C in the shop at the moment, not gonna happen today! 

Jeff

[Darren]

Why not swap the belt for what you over there call a serpentine. That will run on flat pulleys and will not slip.

I did the changeover on my other lathe and now you'd stall the 1.5hp motor before the belt slips. Meaning if you take a huge cut the motor will stall.

[jgroom]

Hi Darren.  Serp belts are Poly V-Belts, don't know if that's a trademark or what.  The mod replaces the three sheve flat belt pulley with a five sheve poly v pulley.  Sounds like a better deal overall and since I'll have to remove the spindle either way......

Thanks

Jeff

[Darren]

Oh I see, Poly V is Serpentine 

I also put one on that really old Union lathe I have and it worked well on that as well..... they get a thumbs up from me .... 

[udimet]

The positve rake inserts are more suitable for small machines ie the CC** DC** TC** SC** and VB** THE SUFFIX GT after the aforementioned letters
 denotes that the insert has a high rake angle [very sharp geometry] that are mainly designed for non ferrous metals and plastics. They do however
  produce a superb finish on STEELS provided they are used for small depths of cut ie finishing passes.  The negative rake inserts are designed to
 be used with high power and high rigidity machines at very high metal removal rates. Some of the negative inserts are as follows,
 CN** DN** VN** WN** SN** [so unless you have a very rigid machine with lots of horses behind it ,avoid].
                                                                                         Regards,
                                                                                     Udimet.

[Darren]

Thanks for that  

Where does XXMT come in as opposed to XXGT?

Is GT a sharper geometry then MT ....

I notice GT is usually specified for Aluminium and often comes uncoated ?

[udimet]

Hello all,
                  Yes,GT is a far sharper geometry than MT.  **GT inserts always have a very high rake angle are uncoated and polished [due to the applications that they are designed for]
            The coating that is used on coated inserts regardless of the coating process [either CVD or PVD] will have the affect of decreasing the "sharpness" of the cutting edge as opposed
 to uncoated inserts.  The MT and MX geometries are designed for Ferrous metals from bog standard EN1 right through to the heat resistant "super alloys"  only the grade of carbide and the chip-
  breakers differ [but that is a subject all of it's own]  Also there are many of the **MT and MX geometries that are known as WIPER inserts [From Sandvik Coromant]  Also bear in mind the ISO
  classification system P, M, K, N, and S  Which relate to in order, Steel, Stainless steel, Cast iron, Aluminium and Super alloys.
                                                                                                              Regards,
                                                                                                              Udimet.
           

[udimet]

 Hi Everyone,
                   Re The post by AdeV the tool that you have is for the following series of NEGATIVE inserts of the following types
CNMG, CNMA, AND CNMM.  and the inserts will be 1204** the 2 stars denote whichever nose radius, you have a choice of the
  following 04, 08, 1.2, 1.6.  As I stated in my previous post These are negative inserts  that require a lot of power and rigidity
 to be effective, I note that the toolholder size is 25mm, that size of shank would be best suited to a lathe of about 215mm
 center height. If you have that size of lathe [or larger] then negative rake inserts would be fine. If your lathe is smaller then
 god knows how you got a 25mm shank into the toolpost [ bit of ingenuity there ]  Really most small lathes are best suited to
 positive rake inserts If you can get hold of a toolholder type SCLC* they utilise the CC** series inserts and you should see a
  great difference compared to the CN series.
                                                                           Regards,
                                                                           Udimet.
                                                                     

[AdeV]

Hi Udimet.

Thanks for your detailed and informative responses! My lathe centre height is approx 165mm - so, from what you are saying, probably not suited to negative rake bits. No problem, I've pretty much put the carbides to one side for now, I'll concentrate on HSS.

As for fitting the tool, that's no problem: My toolpost will take upto 50mm tool steel!! This seems a tad excessive to me, and when I get around to making a QCTP, it will not be on quite such a massive scale... Well, maybe. I already got the steel, and it's pretty damn big...

I think, once I've got the hang of latheing (still a newbie here), then I'll look at carbide again. Although, as mentioned above, my lathe's top speed is only 670rpm, so maybe it'll never be suitable for carbide?

[Darren]

I do have one reservation with using sharper carbide insert profiles. They would be even more prone to chipping.

Prob why they seem to be reserved for alloys by the manufacturers?

[udimet]

Hello AdeV,
                       You should have no problem by sticking to HSS. For your further info HSS lathe blanks are available in a few grades [thankfully not as numerous or complex as carbide].
                       the most common are M2 and M42  the latter has Cobalt added and has slightly more hardness and heat resistance, but is more expensive.
                    Re your toolpost size, 50mm on a 165mm center height your right that is just a wee bit on the large side. My machine at work:450mm center height
                        Takes up to 70mm but weighs in at  12.400 kgs and has 60 kw behind it. so whatever you do dont stick a 50mm blank in it
                                 Keep on practising it's the best way learn. and don't worry about producing scrap early on [I've been there].
                                                                                                Best wishes,
                                                                                              Udimet.