Hi Chris,

Sorry about this it will be an essay but I hope it makes sense and helps.

HSS = High speed steel. A special tough, high carbon tool steel usually alloyed with cobalt (a metallic element, hence cobalt steels) which gives it high wear resistance. It is used for many tools including drills, milling cutters,lathe tools etc. It needs special high temperatures for hardening and tempering and will retain its cutting edge even when running red hot. It was the general; purpose tool steel until the advent of carbide tooling. It is also available as round or square sections to grind your own lathe tools etc but can be bought in preshaped sets for use on lathes etc.

TiN = Titanium Nitride a very hard ceramic used to coat tools, especially HSS tools to add extra hard wearing propertiess to the tooling, it is that gold colour you often see on milling cutters and twist drills these days. It is the same as titanium coating. because of its gold colour it is often used a coating in jewellery. Sometimes only the high wear areas such as the tips of drills are coated

Carbides are carbon based compounds which are very hard but brittle. They are mixed with metals, pressed into shapes and heated until the metal melts and cements the carbide particles together to form a very hard but less brittle matrix. hence its correst name is cemented carbide. The metal gives toughness to the matrix i.e. it is less brittle. Tungsten is often used hence 'Tungsten Carbide'. This is still quite brittle so small tips are brazed onto steel shafts which absorb the shock loads somewhat to produce carbide tipped tooling. Shaped tips which have several cutting edges are often used in lathe and milling tools and when blunted can be turned, or indexed and the next cutting edge used, they are held on a steel shank with special screws. Hence replaceable, indexible carbide tipped tooling.

Many folks use carbide tipped tooling these days but it was really intended for high speed, fast metal removal, production work, the fast removal shortening production times It is quite expensive (at least for me) but in production work the cost of tooling is negligible compared with production time and labour costs. It is not usually worth trying to sharpen carbide tooling,

I prefer HSS tooling for my lathe and mill as it is relatively inexpensive, easy to keep sharp and gives excellent finish on smaller lathes etc. It is easy to touch up and keep sharp once you have learned how to grind the angles, but as only a few basic shapes are required for the vast majority of the work we do this is not difficult.

Best regards

Terry

Another rogue post

Best regards

Terry

Edited By Terryd on 11/11/2012 00:25:09

There's also TiALN – Titanium Aluminium Nitride. This is harder than TiN, but requires high temperatures to function correctly. The theory is that as the temperature rises the aluminium forms aluminium oxide more easily, which is very hard, and which then also prevents further oxidation. High temperature means running the cutter dull red, so no coolant! The coating is intended primarily for cutting harder materials with no coolant, just an air blast to remove chips. I use TiAlN coated end mills for cutting stainless steel and gauge plate.

Thinks: Might be worth trying a TiAlN cutter on HSS to see if it's any better than plain uncoated carbide.

Regards,

Andrew

Terry,

In your Avatar I presume you are the one on the right ?

If so then I have noticed that as you have got older your Avatar has got younger ?

Is there some Freudian connection to this ?

Perhaps you should go the whole way and use this ?

You're the one on the left? I hadn't realised that ,

I'm asking this in ignorance, and not trying to be argumentative. Does the TiN coating not wear off cutting edges fairly quickly? And, on the same theme, is it used more on "throwaway" tools, rather than those which are likely to be resharpened?

Andy

All my metric drills (Dormer) are TiN coated; the coating doesn't seem to wear off even after hundreds of holes. I don't know whether this would be true for lower cost cutters.

The question of re-sharpening coated cutters doesn't really apply. For small cutters it simply isn't worth resharpening. I was talking to the salesman at the industrial tool shop I use on Friday. He was saying customers always ask for a discount on cutting tools. His point was that since the cost of the cutting tools is about 3% of production cost why bother with a 10% discount. A lot of commercial machining is done with CNC machines so if you use a resharpened cutter not only do you have to pay for the resharpening you also need to especially set the machine for that particular cutter diameter and length. Cutters are made for industry, the ME fraternity has to use what is available.

And before anyone jumps in about industry versus ME, I do have a fairly well equipped Clarkson T&C, but it simply isn't worth me sharpening small cutters. I've got better things to do with my time.

Regards,

Andrew

Edit: D**n, Terry beat me to it!

Edited By Andrew Johnston on 11/11/2012 14:46:24

Edited By Andrew Johnston on 11/11/2012 14:47:16

No won't cut better, just stay sharper longer

Not all PVD (Physical Vapour Deposition) coatings are TiN. Much of the current research into tool coatings is aimed at eliminating, or at least reducing, machining fluids by providing a low friction surface to the tool. Tool suppliers sell milling cutters with a variety of different coatings; whether these coatings are relevant to the sorts of feeds and speeds used by model engineers is a moot point. However, for those of us who don't have coolant on our milling machines, keeping an eye on these developments could be beneficial, particularly for milling aluminium alloys where build up of swarf on the tool is an issue.

cheers,

Rod