Drilling hardened A2

Charlie Mike

Charlie Mike

Sober since 1-7-14 (still a Paranoid Nutjob)
Knifemaker / Craftsman / Service Provider
Joined
Nov 1, 2000
Messages
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I'm going to be slapping micarta scales on a Fitzen Crossada. The owner says its .250" A2. I have a 3/16" spiral flute carbide bit. Any specific RPM? Should I do it on my drill press or mill?

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Charlie, I hate to tell you, but what you're trying to do isn't easy. It can be done, but honestly you probably have neither the tools nor experience to do this "correctly". Not that that should stop you from trying. :D

A carbide drill in hard steel has a narrow processing window that you're going to find challenging. I don't think this is something I could do manually on my Bridgeport without tearing up a twist drill.

With that said, these are the things you need to focus on:

The primary problem will be over feeding, which will break down the cutter pretty quickly. The force required to get the drill to cut will be surprisingly high. The web of the drill has to penetrate your work piece (which is made of hardened steel) and a drill web is a pretty blunt cutting tool. The difference between the correct cutting force (fairly high) and too much cutting force (a little bit higher) is pretty narrow. You need to back your work piece with a piece of steel or you'll blow it once the web exits the back.

Chatter will dull a carbide drill. Run it as fast as you can without chatter. This is highly dependent on your mill. I'd run a carbide drill in A2 at 800 RPM but YMMV.

Unlike many of my diatribes about people needing to feed their drills harder, this is not the case here. Underfeeding a drill wears it by abrasion which isn't going to be a problem here (and hard A2 isn't exactly going to work harden much more than it already is). You just need to feed it hard enough that it doesn't chatter, yet not so hard that it breaks down. Good luck with that.

Coolant or oil is not your friend. Honestly, the hotter the A2 gets the better it will cut here. But someone blasting the tool with air will prevent you from recutting fines which would otherwise tear up your cutting edge.

A spade drill or a straight flute drill would be more forgiving.

Please report back with your results!
 
The last time I had a friend harden a knife here and forget to Drill I placed knife in the mill vice and used a 4 flute centercutting 1/4" carbide end mill and with fairly high downfeed pressure and
it went right through. Its not something I do often but I got three holes done in no time with no damage to cutter or knife blade.
YMMV, but if you have a carbide end mill you might want to try that.
CW
 
Hi Charlie,
Nathan is right on the money and really spells it out correctly.
I would add that if you have a lot of vapour in your compressed air it will work against you.
Is what you ask possible? Sure it is.
Would I get it right in my first cutter? That's a question I would only get the answer to by giving it a try.

On a side note for Nathan. When drilling out taps or putting a hole in a dowel pin, carbide ball end mills have worked for me. But I have DESTROYED a lot of ball end mills.
 
Damn Charlie I can't wait to see the results. Give 'er hell buddy!
 
Should I buy/use a carbide ball end mill?
 
Hi Charlie,
Nathan's suggestion was "A spade drill or a straight flute drill would be more forgiving." Is the safest.
What I am use to is the ball end mill. But Jim's point of using the leftover ball end mills to slot some jobs is a Plus on my method.
The answer Should be based on time and money. Safest or my method with a Plus. It is up to you to deside.
Please let us know how it turns out.
 
Hi Mete,
I had access to a sinker EDM and had used it in many applications like this. But again it comes down to money. Shop time can cost a lot.
Sincerely
Dave
 
I use diamond coated twist or core drills any time I have to cut hardened steels, I just keep them in a light oil puddle and use high rpm and very light pressure

I haven't dealt with these folks, but they don't require you to be in the jewelry trade to buy, and they seem to have a good selection, this will give you an idea, and a quick google search will bring up a host of different sizes in both types of drill

http://www.dadsrockshop.com/diamond_drills.html

-Page
 
I would not suggest using a ball end mill bit for this application. I am not saying it will not work, but I am saying I have personally failed attempting to do it this way. the flutes on the point of the ball end mill are fairly fragile and I chipped them before getting through the last time I attempted this.
CW
 
Can you anneal just the spots you want to drill in the handle area?

I mis-located a couple of holes in the last fighter I made of CPM154 stainless and had it hardened before I realized what I had done. Using a regular propane torch, I heated the spots as red as they would get for a minute of so, backed off slowly, let them cool, and drilled the holes with a cobalt or regular HSS bit. It wasn't as soft as fully annealed would have been, but it worked just fine. I have done that a couple of times, but don't know if tool steel would act differently?

You would not want to let the blade to get hot of course.
 
That is another way to do it. I have had pretty good luck drilling holes with ball end mills, but, I haven't had to drill that many. But, I have collected up cheap carbide end mills and had them available.
 
If you don't have tight tolerances on the holes you could try carbide tipped masonary bits. You might need a fresh bit for each hole. I use a carbide spade bit for tighter tolerances.
 
Bo T said:
If you don't have tight tolerances on the holes you could try carbide tipped masonary bits. You might need a fresh bit for each hole. I use a carbide spade bit for tighter tolerances.
Click to expand...

I think I'll go that route. Tom Krein also told me the same thing.
 
Bo T said:
If you don't have tight tolerances on the holes you could try carbide tipped masonary bits. You might need a fresh bit for each hole. I use a carbide spade bit for tighter tolerances.
Click to expand...

That's what I was going to suggest. You can get them at any hardward store, and they're much cheaper and more disposable than solid carbide end mills. If you're epoxying the scales, hole sizes in the steel don't need to be exact. That being said, a 3/16 carbide tipped masonry bit MIGHT give you the needed clearance for a 7/32 shouldered corby rivet.

Like Nathan said though, you will want to take care not to blow out the steal upon exit of the bit.
 
I just did a blade the other day that was hardened and needed a different hole location. I marked the hole location and blew a small hole with a plasma cutter. Heating is very localized with this short of a burst so no worry about the temper. I marked the hole out again and finished it out with diamond burrs in a foredom.
 
I've used carbide tipped spade bits and they go through hardened steel really quickly. I have read that you might need to reprofile the tip for steel if you get the masonry ones.

I have some of these that are multipurpose:
[video=youtube;ZdSim29sStw]http://www.youtube.com/watch?v=ZdSim29sStw[/video]
 
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