Tungsten Carbide Tipped Lathe Tools

More out curiosity than need I have recently purchased a Tungsten Carbide Tipped lathe tool. Consistent with what I have read, it needs much higher speeds and deeper cuts to make it work well. Does anyone know why it needs different conditions to a HSS tool?

Thanks

Bob

You can run any tool at any speed. However, if you run to fast, the tool gets to hot, loses strength and gets blunt fast. If you run to slow, the chips will be cold and tough and the tool gets blunt.
At higher speeds, the chips get hotter and softer resulting in a better finish. The same when feeding faster or taking deeper cuts.
Also the chip breaker on the tip is designed for certain range of speed, feed and cutting depth combinations.
At some point, your lathe/mill will start flexing when the stock has impurities or is inconsistently and your finish will be lesser.

Larger inserts can take heavier cuts and are more likely designed for rigid machines. On my hobby machines, I use small insert like CCMT060204, DCMT070204 and TCMT110204.

I run HSS at 30 m/min on steel.
Most of my carbide inserts go from 90..300 m/min on steel and I try to run these at their max speed.
I run my brazed tools at the speed of HSS. Never tried to run faster and I don't use them often!
For finishing passes, I feed at 0.05 to 0.1 mm/rev and use a 0.2 to 0.3 mm depth of cut.

Edited By Huub on 16/05/2023 23:46:32

Edited By Huub on 16/05/2023 23:47:09

Edited By Huub on 16/05/2023 23:47:52

Many TC tips have a slightly rounded edge to avoid cracking as the material is brittle. They need to be worked harder to get the required heating/softening Huub mentions.

I've always wondered what brazed carbide tools are for? In my workshop they combine the resharpening disadvantages of HSS with the brittle disadvantages of Carbide.

My guess is they're good on a slow lathe when it turns large diameters work. The large diameter results in a high-surface speed even at low RPM, creating a condition where Carbide removes more metal faster than HSS, and the edge lasts longer. Double good if there's no tool-change speed advantage in using relatively pricey exchangeable inserts.

The small brazed carbide sets seem particularly useless. They often come unsharpened and perform badly until touched up on a green wheel that I don't have. Yuk! Someone must like them, perhaps I'm missing something?

Dave

As a rule of thumb 150% faster speeds, then heavier roughing cuts. Tipped tools unless small radius tips do not like fine cuts.

Hi All,

Thanks all that seems quite logical.

So the follow up question, and I don't know why anyone would want to do it, but if a TCT tool was ground so that it didn't cut so well, would it generate more heat and then give a good finish at lower speeds and feed rates?

Bob

SOD,

I have a couple of the garbage brazed Carbide Tools you mention. They came with my 9" South Bend Lathe when I picked it up second hand. The only use I have found for them is for the rough Cuts on Cast Iron Locomotive Wheel Castings. I have machined Wheels up to 6-1/2" diameter using them. They are a pain to use on the South Bend with its "Lantern" style Tool Post. To obtain a close to 0 degree Top Rake requires shimming under the "Boat" Assembly of the Tool Post. They do function per your Statement " My Guess they are good on a slow Lathe when it turns large diameter Work". For finishing Cuts on the Wheels, I revert back to good, old HSS. I use 1/4" square Tool Blanks, all ground by Hand. The 1" wide Flat Belt Drive to the spindle can hardly handle anything more.

The problem you have discovered relates to the fact that cutting tools, to cut stuff as hard as steel, need to be rigid, unbreakable, heat-proof, and not subject to wear. Few materials come anywhere close, but there are alloys of steel which come close. But they are not as hard as some materials such as the carbides* of various metals, and diamond (which is so rare that its use is naturally restricted). The problem with them is that they are difficult to make (or dig up) in large enough pieces. One good trick is to use powdered carbide, stuck together into a solid block, by the use of clever brazing alloys, or the process of sintering - heating a compressed block to near melting point and increasing the pressure until the whole lump becomes solid. Either way, the result is not as fine-grained as steel, so cannot take such a fine surface finish. With tools that by their very nature have a rather rough surface, it is not possible to get a really razor-sharp edge, so they cannot cope well with a very light cut - but, with the advantage of their extra hardness, and heat resistance, they can cut much deeper and quicker than tool steel. As long as your lathe is strong enough and powerful enough to withstand the extra loads this creates.

* a carbide is a compound of carbon with another element. Several carbides offer useful properties which make them very useful in engineering. When old fashioned carbon steel is hardened, it is the iron carbides which give the desired properties, for example. Another 'everyday' carbide is Silicon Carbide, so hard and tough that it is used as an abrasive to cut and polish hard steel etc.

I hope this helps - regards, Tim

I would not say brazed carbide tipped tools are garbage, before the advent of indexable tools they were used a lot in industry. I still use mine though not so much now I have indexable tools. That Minnie in my avatar was machined mostly with brazed tipped tools some 30 years ago and they were used on all materials. I was only using one at the weekend as the tip radius and angles suited the part I was machining.

Most supplied ones don't need grinding, just a bit of work with a diamond slip as the basic shape has already been ground for you.

If you want to take light cuts with carbide inserts then get the **GT will do that. Or PCD inserts if you have deep pockets

Edited By JasonB on 17/05/2023 16:26:12

Carbide was developed for industrial use where time is money, so higher speeds and deeper cuts save time.

The theory behind being able to cut harder materials, is that at the point of contact between tool and work, the friction produces high temperatures.which softern the material, locally.

To get the best out of carbode cutting tools, the machine needs to be able to withstand high speeds and deep cuts. (Older or less rigid machines with plain bearings are not suited for this sort of maximum capability work. )

Carbide will take small cuts, and at low speeds, and produce good surface finish, but this is not why they were developed!

Moulded carbide tips have rounded edges. Ground imserts have sharper edges, but are even less tolerant of being banged, and chip, more esily that the moulded ones.

HSS is more tolerant of interrupted cuts or hamfistedness!.

For turning hard materials, they are invaluable. Turning some case hardened spacers, the swarf came off like red hot wire!

My lathe has roller bearings in the Headstock, but t a lot of my turning work mis done using HSS (A Tangential Turning Tool) but for roughing and for boring, I use carbide tips (CCMT0604 )

HSS has the advantage that it can be reground at 8 pm on a Saturday night when carbide insert stockists are safely at home.

A length of HSS will cost about the same as one carbide tip, but can be reground many times, withoutb the need for a special grinding wheel.

Literally, you pay your money and make your choice, of the tool for the job in hand.

As hobbyists, we are not on piecework, nor trying to make 5,000 identical items.

Howard.

You can also get these:

https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Carbide-Inserts/SCGT-Square-Uncoated-Carbide-Inserts-Non-Ferrous-Metals

Despite the stuff about being for non-ferrous metals they actually perform very well on steel, especially the free-cutting variety,

The rake geometry limits depth of cut to about 1mm, but you can take very fine (0.01mm) finishing cuts. They work well at high and low speeds.

They will withstand cast iron but wear quite fast.

I use them all the time.

The wheel castings on one of my locos had some really hard spots. HSS wouldn't look at them and inserts chipped. Brazed carbide sVed the day, but that's the only time I've found them useful.

Why do they call these tool tips "Indexable" ? is there a connection to the word Index

You can rotate them round in their pocket so they are indexable by 2, 3, 4, 6 or 8 positions depending on the overall shape of the insert

Thanks for all the advice. Sounds like non-ferrous tips should be the next tct experiment for me.

I am a bit confused about the types of indexable-?

1-I have a set lathe carbide tools 10mm which all of them in my opinion is 100% indexable as a set. I can set the toolholders on a flat piece and their tips cutting are all on same height. This means I can set up one of these on centre, lock the toolholder in QCTP and every other one will be on same height, you can even stop their lenght as well in holder.

2-I have another set of 12mm toolholders but this set is not 100% indexable. In this case some of them are on same centre height, the others are not. So in this case I cannot swop them in same QCTP holder and expect it to be adusted right, so here a rich man has a QCTP holder for each.

3-Then if one narrow it down to any of these but only the same insert in same toolholder, one could argue it will be indexed everytine as long as only the insert is changed.

-Sometimes I slightly grind the parting tool tip(Iscar) sharp with a dremel diamond grinder, fast and easy, it then eats the metal, otherwise I have to push it hard to overcome the initial resistance, I dont really like this on my 330 lathe..
-Mostly I set tip on centre, if it then seems to rub, I move it down slightly, it then cuts freely, for boring you move it up on the inside.
-I found that quality inserts like Iscar, Walter, and other holds noticibly longer and are tougher than the chinese cheaper ones. It helps if one use the tool as intended for.

--Two other things confusing me a bit is cutting with sides of inserts on Positive/Negative raked toolholders understanding that inserts were made for the type. However if the tip is on centre or just below or just above as desribed before, the side will not be on centre anymore, so there goes the around centre cutting.
--The other thing is given any tip in any type of toolholder, if you take deeper cuts which happens now your hobby lathe has more flex as a heavy sturdy large lathe and because of the pressure the tip is now way under centre compared to a light cut(Exaggerated a bit for explanation), so how many of you have ever measured the dive a tip take when cutting from a reference point with a test dial indicator on insert-?

Whilst the above explanations may be appliccable, I reckon it may simply be traced back to when these items were introduced - as organised listings of available cutting tips which could be used on the first simple range of cutter holders. Just like the index of a book, really.

’Inserts’, I suspect, was the term used immediately before the concept of ’indexing’ them was coined. Simply a descriptive word that caught on and has been totally accepted as the normal terminology in the sector. Words are introduced in many technologies - often using words that have been previosly used elsewhere. One obvios (to most) might be the word ‘router’.

Indexable isn't the same as interchangeable, but saying that inserts of the same shape, dimensions etc, etc will be  interchangeable within the tolerance of the insert manufacture. 

Tony

Edited By Tony Pratt 1 on 22/05/2023 10:57:22

Possibly why the historical advice given in this thread applies?

Rob

Links to https://www.model-engineer.co.uk/forums/postings.asp?th=186489

An indexable tip can be used in more than position in the holder.

(Like Jason, I do not get on with brazed carbide; They seem to chip very easily )

A typical one is the CCMT0604. Thisis a moulded diamond shaped carbide insert.

In most holders the 80 degree corners can be used. So the other cornewr can be used, when the first wears or chips. Greenwood Tools (Sadly, now gone ) used to sell a holder which allowed the two 100 degree corners to be used.

Triangular inserts have three curners and cutting edges that can be used.

As a generallisation, a carbide tip of one type can be interchanged with another of the same type, without problems (They probably came out of the same mould! )

Round tips can be gradually rotated until totally useless. But a wide cutting edge can encourage chatter, so to begin with, stick to single point tools.

Unless you want to use HSS.

A HSS toolbit can be reground many times, with an ordinary carborundum wheel (Carbides need either a special wheel or a diamond wheel )

Also a HSS toolbit will cost you about bthe same as one carbide tip.

BUT, you will need a bench grinder if you have not already got one, and will need to learn how to grind tools; not difficult.

HSS or Carbide? Horses for couyrses.

Carbide will cut hard materials that will blunt HSS.

HSS can be ground to a "Bespoke" shape if required.

Whatever you use, it needs to held rigidly on centre height, if it is to cut properly. (A tool that is held less than rigidly is likely to chatter )

HTH

Howard