Bargain at B & Q

At eight pence per bit do you really think Chinesium will drill through anything more than butter.

My neighbour gave me some HSS drills he bought from UK Drills in packs of 10 and he didn't need them all so gave me some. I tried one on some stainless and the stainless won easily, my Hertel HSS drills dealt with the stainless easily. I'll keep the cheap ones on the side for soft stuff like wood and aluminium.

I've been 'pleasantly surprised' by cheap drill bits in the past. I tend to have a 'good' set which are for more demanding jobs and a cheap set for run of the mill diy work. The cheap set are typically like those mentioned.

As is the way with things- sometimes I can't find/don't have/have broken/etc the drill bit I need for a demanding job and I've used one of the cheap drills.

They may not 'hold their edge' so well but I don't recall not being able to drill even stainless steel (which I do occasionally).

All in all, probably not a bad buy- but wait until Wednesday if you are

On a more general point, does anyone know the idea behind having a titanium coating? It is a metal which seems to be 'popping up' in all kinds of things. I know it is strong, light etc, but it almost seems to be 'fashionable' recently. (I like insulted coffee/tea mugs, ideally metal. My latest addition to my collection is titanium. It is supposed to have all kinds of 'benefits'- I just liked it and wanted to keep my coffee/tea hot.)

That's just advertising speak, they are actually coated with the compound Titanium Nitride which is harder than steel at 9 on the Mohr (Moh?)scale just below that of diamond.

Alan

Thank you.

More of a rhetorical question, although someone may know the answer: Presumably the coated finish is more akin to 'case hardening' that the hardening and tempering (limited for drills etc) used for tool steels etc.

(As I understand it, case hardening is more of a surface treatment. Heat treatment and tempering tends to be more than 'skin deep'. )

I think for drills and milling cutters, it is usually applied by PVD (Physical Vapour Deposition) as a very thin coating using an electron beam or by "sputtering" or a cathodic arc to coat very tiny particles of TiN onto the surface of the steel where they become part of the crystal structure.

Alan

Interesting, thank you. The end result does sound more akin to case hardening than a bulk heat treatment then in that there is a thin layer changed due to an additive. Of course, the nature of the change in the structure may well be different, just as the additive is.

I remember using case hardening at school when making an adjustable spanner (which I still have, 40+ years on). We also made screwdrivers and an ordinary spanner- unfortunately I've lost those.

I think that would depend on how it is bonded to the steel

It should be 'more than skin-deep'. There is a real art in hardening and tempering some tools: hammer heads for instance, should be tough on the inside and hard on the faces - not easy to accomplish.

That was part of the question.

Aren't they forged to provide the 'inner' toughness then heat treated to provide a hard surface.