Drilling Hardended Carbon Steel

[Volvo_ST1]

I have to drill a hole in hardened carbon steel. The piece of steel is 4.5 mm thick. There's already a 3 mm hole in this piece. The hole has to be widened to 3.8 mm.

Then I have to drill three more holes with a hair under 1.5 mm diameter. There are no pilot holes.

The piece of steel I have to drill is round and has a diameter of 11.35 mm.

What kind of drill bit do I need, and where can I get it?

 

[simple_gifts]

Any particular tolerances? Is the face of the steel cleanly machined? Do you have a Bridgeport or do you expect to do this with a power hand drill?

hole making

 

[Volvo_ST1]

The 3.8 mm hole can be +/- 0.05 mm. The 1.5 mm hole should be a smidgen smaller so that I can hammer 1.5 mm steel rods in without having them fall out.

If I had a Bridgeport or [censored] I'd probably know how to drill holes. I have a small drill press. Top speed is 15,000 rpm.

Do I need diamond-tipped bits? Self-annealing bits?

 

[tgw323]

What you need is carbide. What carbide needs is a rigid set-up. The bearings in your small drill press and whatever kind of vise set-up you have won't make the cut. You could buy a dozen drills and give it a stab, hoping that the 12th one manages to make it, but I doubt it. Sounds like a job for a good machine shop-not cheap.

 

[Pablo]

How hard is the steel? Slow and cool with a hardened tool steel might do it, or a cobalt bit. Diamond may not be precise enough, but it would work.

 

[A_Harman]

Any decent machine shop should be able to do it for ~$50.
Carbide drills can do the job. The problem comes when the drill breaks out the other side and get snagged on the burr. This will break the drill instantly unless you can control the feed rate, which is very hard to do by hand.
High speed steel drills can probably do it, and not be as prone to snapping as they break through. You would probably need a fresh drill for each hole.
Whatever you try, be sure to use plenty of lubricant.

 

[volvomix]

what is a a "cobalt" bit?

You can have tool steel, Titanium carbide coated, and Tungsten carbide, and that about does it.

 

[Pablo]

Originally Posted By: volvomix
what is a a "cobalt" bit?

You can have tool steel, Titanium carbide coated, and Tungsten carbide, and that about does it.


Quote:
Cobalt steel alloys are variations on high speed steel which contain more cobalt. Their main advantage is that they hold their hardness at much higher temperatures, so they are used to drill stainless steel and other hard materials. The main disadvantage of cobalt steels is that they are more brittle than standard HSS.


http://en.wikipedia.org/wiki/Drill_bit

http://www.google.com/search?hl=en&s...mp;oq=cobalt+dr

Plus there are many other more exotic hardened tools than the few you list.

 

[suspiciousmind]

I think I'd start with carbide endmills (square end) in your drill chuck. It would be friendlier enlarging the existing hole and less prone to drifting on the cylindrical surface when starting the small holes..

Ordinarily low RPM andslow feedrates would be in order but, since you're hand feeding it, I think I'd try high RPM and peck it with lots of lube involved.

Wear eye protection!!!!! and clamp your part down really good....a rigid set-up is important.


The company I work for builds waterjet systems. that was the first solution that popped into my mind. there are at least three buisinesses in my town that use them and, if you have access to one, do it. the holes will need to be through both sides of the part though.

 

[volvomix]

pretty sure I am aware of them since I am a metallurgist.

When someone uses the term cobalt it can mean or be interpreted as a lot of things. I think M42 is alloyed with cobalt as opposed to convention HS drills that commonly use M2.

Cobalt doesn't form a carbide, it just is soluble in the matrix and helps elevate the tempering resistance of the drill.

 

[Volvo_ST1]

Thanks for the input, everyone. It looks like my equipment can't get the job done. Having this part machined is out of the question, because it's just not worth the cost. Machine shops here charge generally around $100 do to anything. For considerably less than that I can get a suitable original part.

 

[A_Harman]

EDM is a way to do it also, but the recast layer left from burning the metal away makes the zone surrounding the hole very much prone to cracking. The part should be polished or ground to remove ~.005" from the surface to remove the recast layer.

 

[simple_gifts]

+1 on the center cut end-mill.

 

[Volvo_ST1]

How was this done with high precision 90 years ago?

The flint wheel in the picture is the part I would like to replicate.

 

[Rick in PA]

I assume they'd make the part with the steel in the soft state, then harden the steel.

I've had some luck drilling harder materials with bits like these.

 

[Volvo_ST1]

Originally Posted By: Rick in PA
I assume they'd make the part with the steel in the soft state, then harden the steel.

I've had some luck drilling harder materials with bits like these.


And wouldn't drilling hardened carbon steel heat the steel enough to soften it, which might require hardening it again? I really think it's not worth even trying.

 

[expat]

Does Boeing still have a surplus store south of Seattle?
I used to get some real nice, low cost drill bits there.

 

[Volvo_ST1]

They closed a couple years ago.