View Full Version : Drilling through Tempered Metal

15-10-05, 08:03 PM
I have a full tang blade that requires the pin holes enlarging.

The hole tang is hardened, so my question is how do i drill through?

Sorry if this is a dumb question!

Colin KC
15-10-05, 09:04 PM
Shinken, protect the blade & torch the holes;)

15-10-05, 09:05 PM
8% cobalt

Colin KC
15-10-05, 09:08 PM
8% cobalt

Yeah Mushy, like everyone can afford cobalt bits:rolleyes:

15-10-05, 09:12 PM
Do you need to use cooling agent for colbolt bits?

15-10-05, 09:16 PM

Keep it slow and cutting fluid always helps

15-10-05, 09:55 PM
If the holes are already quite large, you can enlarge them with an abrasive stone in a demel type drill.

16-10-05, 12:27 AM
If you have a powerful enough drill, bully your way through with a tungsten carbide masonary drill. No cutting compound or coolant needed, and boy, do the sparks fly!!

Cobalt drills are not proofed against hardened steel, and I have TWO burned and very expensive tips to prove it.

I took the blade to my local commercial circular (Forestry type) saw blade maker. He put the bit in a chuck the size of a small car, in a drill press the size of a bus, started it of at 11 RPM, and put all his weight on the lever. It wailed like a banshee, and sparked like Harry Potters Patronus, but it went through.

I tried it at home with a 1/2 hp pillar drill. It took a while longer, but it did cut.

16-10-05, 07:06 AM
Please don't fight a hard tang. There's easier ways.

Yes, if the metal was HSS, tungsten or a fast air hardening steel, you'd probably have to hog your way through or burn through. I have used plasma, diamond bits, cobalt bits, ti-coated bits, carbide bits, masonry bits, etc. These methods are fraught with inaccuracy, can weaken the tang, can be dangerous to do and require expensive and easily damaged equipment.

However, knife blades are not made with HSS. At one point during the manufacturing process the blade was annealed and could cut easily. The challenge is just to temper the part of the tang you want to drill till its soft without affecting the HT and temper of the blade itself.

All you have to do is selectively heat where you want to drill. I use an oxy-acetylene torch with a very fine nozzle, but there are other methods that work. Oxy-acetylene's advantage is that the flame is intensely hot and you can quickly get that spot up to temperature before the surrounding metal can be affected. I saw a nifty idea once on BB where someone suggested you used a blank faced rod in the drill press to heat the spot up using friction; I haven't tried it, but I have also seen it in a drilling textbook. Alternatively, you could lay that part of the tang on an electric kitchen hob. Once the spot is sufficiently tempered, it should be easy to drill.

If it's still impossible, you might consider fully annealing the whole blade and re-heat treating it after you do the drilling.

16-10-05, 09:04 AM
Localised heat can work well, but if it is 01 and you heat it above critical temperature, it will air harden as it cools and end up even harder :(

Lower carbon steels like CS70 are fine for this technique.

16-10-05, 09:35 AM
Cheers chaps, i will buy some 8% colbolt and try it on an old full tang i have and see how i go!

16-10-05, 10:22 AM
Localised heat can work well, but if it is 01 and you heat it above critical temperature, it will air harden as it cools and end up even harder :(

Lower carbon steels like CS70 are fine for this technique.

O1 air hardens!?!?!?!?!

16-10-05, 11:08 AM
Unfortunately I have found it does.
It is classed as an oil hardening steel, but when I started forging it, I found I couldn't touch it with a drill afterwards unless I had annealed it using delayed cooling like leaving it in hot coals for a couple of hours.

When my blacksmith tutor and I discovered this we couldn't understand it, but he has looked it up, and it is due to the very high carbon content (1%). It is a real pain, and is one of the many reasons why something like 1080 is a better simple knife steel. Trouble is getting hold of 1080 is a lot harder in the UK :(

16-10-05, 11:18 AM
1080 and 1095 are pretty close to 1%...

16-10-05, 11:40 AM
I think that its the (relativlely) high chromium content of O1 which causes air hardening. Chromium increaces the 'hardenability' of a steel. O1 is intended to be used for industrial tooling which sometimes has quite large sections, the chromium content makes it easier to harden chunky parts all the way through without cracking.

16-10-05, 07:03 PM
Thanks for that Chris, nice to know why my steel is such a pain :)

20-11-05, 06:46 PM
You can make holes in already hardened steels with tungstene bits used for concrete.

You must first sharpen it to give it a positive angle (for concrete it's negative) and then you can make holes !

Then, while using it, it'll become RED hot ( tungsten fusion is around 3000C but steel will be soft before !)

It makes approximative holes, but it works !


20-11-05, 06:48 PM
Thats a brilliant series of pictures! Is it my imagination but does the bit appear to change shape in the last picture?


20-11-05, 07:59 PM
O1 air hardens!?!?!?!?!

O1 is an oil hardening steel, but there is something like a 10 seconds window to drop it below the nose of the curve (from critical temperature to somewhere around 1000F)....so its quite possible that O1 will harden in the air, .. it may not be a full martensite harden (so not a true air hardening), but hard enough to notice with a drill!!..Compare O1 that with something like 1095 which has a window of around a second and 52100 which is around 3 seconds....

20-11-05, 09:05 PM
I have found that if you want to keep the blade of a full tang cool whilst burning through a hole through itis to stand it in a McDees coke cup full of water and ice. then just hit the hole with the gas axe and bobs your uncle.

21-11-05, 08:33 AM
HOw on earth do you sharpen Tungsten???:O

21-11-05, 01:28 PM
the bit appear to change shape in the last picture?
I didn't made those pictures, they came from the net, i've lost the link :(
It was a company making those special bits. But the effect is similar

HOw on earth do you sharpen Tungsten???
Sharpen isn't perhaps the good word : just give a positive angle with a standard grinder.

This is not a fine and precise technique, but you can use it in need !

21-11-05, 02:05 PM
tungsten carbide can easily be sharpen using a diamond stone, I see if I can drill a hole through an old file tonight.

21-11-05, 02:28 PM
I use tungsten carbide, for machine tools, and improvised scraping tools. All are sharpened (loose term as TC doesn't like been a razor sharp edge) with diamond stones. Be aware TC has an aversion to steel (could be high carbon?), if you have a fine edge on the TC, the TC will chip and crumble, so watch you don't aim for an edge you would normally use on HSS tools.