Will cobalt drill through hss?

[challenger]

I need drill through a hardened mt2 taper. Will cobalt do the trick or do I need to buy a carbide drill bit? I'll be using a mill not a drill press. The hole will be 1/4".
Thanks

[nickel-city-fab]

Not necessarily. The cobalt alloys are not necessarily any harder than HSS, so I would use carbide for that job. The advantage of cobalt is that it stays sharper longer, especially at high temperatures. But it isn't necessarily any harder than HSS.

Kinda curious what are you building that requires drilling HSS?

[Jim Stewart]

HSS seems to me to be an odd material for an MT2 taper. Sure it isn't just hardened steel?

-js

[MattiJ]

Not a change in hell to drill hardened HSS with cobalt(-HSS).
But like Jim said the MT2 taper could be something else than high speed steel.

[old mart]

I would go for carbide, using a rigid setup or the risk of shattering the drill is high. The Morse tapers on twist drills are not usually tempered as hard as the tips, but even in that case the cobalt might end up melting. A lot of people get hold of old masonry drills and sharpen them with good results. Bosch do sets of inexpensive multifunctional tipped drills which will drill through hardened steel even using a hand held drill as the shanks are not brittle. This is what I have:

https://www.amazon.co.uk/Bosch-26070.../dp/B001L1RAYQ

[challenger]

Not necessarily. The cobalt alloys are not necessarily any harder than HSS, so I would use carbide for that job. The advantage of cobalt is that it stays sharper longer, especially at high temperatures. But it isn't necessarily any harder than HSS.

Kinda curious what are you building that requires drilling HSS?

I'm trying to make a jig and I'm using an R32 collet chuck that has the mt2 taper. It isn't a removable taper. Perhaps it is hardened steel and not hss but it doesn't hardly get a scratch with a hss drill bit. It is for sure hardened chinesium of some sort. I suppose I could anneal it???

[nickel-city-fab]

I'm trying to make a jig and I'm using an R32 collet chuck that has the mt2 taper. It is for sure hardened chinesium of some sort. I suppose I could anneal it???

You could probably anneal it but I wouldn't want to. Annealing it runs the risk of warping a ruining the surface finish and dimensions. I was looking at those bits Old Mart mentioned, they're sold in the US as "Bosch Daredevil" bits in the masonry drills section at Home Depot.

[Toolguy]

I would use a straight 2 flute solid carbide drill with no lube.

[MattiJ]

I'm trying to make a jig and I'm using an R32 collet chuck that has the mt2 taper. It isn't a removable taper. Perhaps it is hardened steel and not hss but it doesn't hardly get a scratch with a hss drill bit. It is for sure hardened chinesium of some sort. I suppose I could anneal it???

For sure its not HSS in that case. Case hardened 1045 or some low end tool steel. Carbide drill or center cutting endmill will handle it.

[PStechPaul]

You could also try diamond drills or burrs. They are pretty cheap and will cut pretty much anything. But they need high speed and may not drill a very clean or accurate hole.

[dian]

how are you drilling? make a dimple with a dremel bit larger than the chisel. then go slow (like 60 rpm) with max pressure. a regular hss drill shoud work. cobalt is a little harder (5 hrc points). worth a try, imo, before sourcing a carbide drill/endmill. dry.

[thaiguzzi]

HSS seems to me to be an odd material for an MT2 taper. Sure it isn't just hardened steel?

-js

Yep, never seen nor heard of MT2 HSS.
OP is just using the wrong terminology.
Lets just say the MT is well 'ard.

[challenger]

I'll give the cobalt drill bit a try. I certainly used the wrong terminology in calling the MT2 taper, HSS. I guess I should have said hardened instead.
Thanks

[dian]

could have been an mt taper drill, but if the shank is hss who knows.

[old mart]

Bosch Daredevil, eh, trust you Yanks to come up with a stupid name, but they are very good. Their original concept was to be able to drill through wood and into the wall of the house, thereby eliminating the problem of misaligned holes. Mine will not go near any wall, I keep them for drilling hard steel. As I said earlier, you can use them in a hand held drill without worrying about snapping them. One of these days I will try out my diamond wheel (electroplated type) to sharpen up some straight shank masonary drills, they have no use now in the era of SDS.