Cobalt drills?

At a few ME shows i have seen an exhibitor merrily drilling holes in hard steel files, bearing races and so on and selling the drill sets. I need to make a dowel hole in a non-standard place in my Dickson QC toolholder block - does anyone know please, are these "cobalt" drills? My local Toolstation has reasonably priced sets, they claim they can work on hardened steel.

Can’t tell. Who knows whether those files are properly hardenened? Usually , if really cheap there is a catch. Buyer beware!

Same as glass cutting demos - they are cutting 3mm soft glass, not your usual 4mm float.

Masonry drills, resharpened to a suitable angle, can be good for hard steels.

Cobalt drills are capable of drilling harder material . I have had some experiance drilling stainless steel with them , however with regular use the will become blunt very quickly and either need replacement or to be sharpened. The most imortant thing is to not buy coated drills or tipped as you cannot resharpen them.

I noticed that Chronos were doing a set of solid carbide drills from 3 to 8mm for £38.40 but they are out of stock at the moment. I would say that this is the way to go.

David.

You say you want to drill a hole for a dowel, even if these drills will make a hole, holding the tolerance for a dowel fit is another issue.

Mike

Thanks, will make the dowel to fit the hole.

Cobalt drills are just tougher HSS - M34 or M42 depending upon the percentage of Co added to the alloy.

I would go with carbide for hardened steel even if it is just case hardened.

HTH

Jon

I think the tool post is case hardened. A local grind with a dremel or start the hole with a carbide cuttter should do it.

I advise to avoid carbide drills as they shatter easily and are difficult to remove the debris even with a spark eroder.

As far as drilling bearing races - make sure you take your own along , to be sure of the capabilities.

Here is a fine example of what could be drilled with a HSS drill. High quality chinese bearings!

**LINK**

John, if the drills you're referring to are the ones that are (or used to be) sold in sets in a flat grey box at ME shows, then yes they are capable of drilling hard stuff, though I'm not sure about accuracy.

They need to be run pretty fast, and initially skate round on the surface to be drilled, as centre punching isn't going to work very well. Better to prepare a guide piece, with the requisite sized hole and and clamp the workpiece between that and some backing material.

I've a Manchester Rapidor Minor mechanical hacksaw, which only takes 9" blades, so I buy longer, all hard, ones and use these drills to add the new hole in the end when I've shortened the blade to length.

You do need to support the break through side though, with something reasonably hard, to avoid chipping of both the bit and the workpiece.

As far as the demos go, yes they seem to be real files. I've tried drilling HSS blanks, and the bits cut through those OK.

Bill

Edited By peak4 on 04/03/2018 11:24:19

If its case hardened just use a sharpened masonry drill then hss

Slow speed high torque is the way to go with tough jobs

I'm sure the cobalt drills would be good, but expensive

John good luck with a cobalt drill on your Dickson tool holder block, I had to open out the mounting stud hole on the one I recently fitted to my lathe, I needed to open out the hole from 11.2 mm to 12 mm, you would think that would have been easy, it certainly wasn’t. The hardened alloy steel just wrecked a number of cobalt drills and left me wondering how I was going to achieve the objective, I decided in the end to use a diamond core drill, obtained from Arceurotrade, they had a 12 mm size one and it was only about £4 or thereabouts, it did the job and easily ate it’s way through the toolpost, although I was only using it to remove .8 mm from the hole so I don’t know how you would cope with a solid hole, if you know what I mean. The hardened alloy steel that they use is incredibly hard, most cutting tools just bounce off it, have you thought about having the hole spark eroded? Let us know via this thread how you get on? Dave W

Re the idea of spark eroding the hole. Find someone with a wire eroder, similar process but faster and cheaper plus more accurate. I have operated both machines so speak from real experience. A 1.0mm start hole for the wire to go through will take just a few minutes on a proper machine.

Stellite / Inconel drills. Drill at very high speed and pressure and the swarf comes off glowing red.

carbide will tend to prefer high speed over lower speed, so the heat generated from the drill helps carbide do it's work. But at low speeds you wont really be getting a whole lot of benefit from that, any steel that was harder than what you were drilling would work just as well in that scenario.

Michael W

Pierre's Garage reviewed some HSSCo drills from Banggood and they seemed OK. I got a couple of sets - at that price and reasonable quality, it would have been rude not to. They seem to be good up to about HRC50, which is fairly hard but not full witch's tits, as JS would say.

Tried to drill into some surface hardened steel last week and it buggered an HSSCo drill. But a carbide end mill got through the skin no problem. OK once under the skin of course.

Murray

I have used a resharpened masonary drill bit to drill very hard steel.

Drills bought, work a treat on the hardened block. Not quite hot knife+butter but no sign of overheating or distress. Recommended.

And a 6mm drill produced a hole that the 6.02mm shank of another drill fitted nicely.

Stellite will drill any hardened steel including HSS it needs to be used at high speed. As it runs red hot it may leave the sides of the hole in a carbon steel soft enough to follow up with HSS, I've never tried that though .Colin