Guidance with drill bits needed

WadeH said:
I finally got the holes drilled and have done the heat treat and have them in the oven now cooking. I tried the Masonry bits they worked pretty good. I had already tried at Tit. bit and a Cobalt coated bit and they did not even finish one hole. I was really surprised that the Masonry bits worked like they did, I would have never guessed that it would. It is funny that the smaller bits with cut through this 1084 pretty good, it is when I move up to something like a 1/4 inch that I have problems. Makes me wonder if somehow I am hardening the 1084 with the first hole or with the bigger bits.
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That tells me you might not be feeding it hard enough.
 
If a person were to use the Colbalt bits, and only buy what is needed. What would be the most common bits, let's say the first 10?? Or would I be best to buy a full set???
 
Hi James - all of the CPM steels and pretty much any air hardening steel come dead soft. They are generally very easy to drill unless there's already been some heat treating work done to them. 10xx steels will vary in hardness depending on CR/HR/(A). In my experience, even HRA/CRA 10xx series steels will have hard spots, my experience with annealed air hardening steels has been much more consistent.

My belief is that this is due to the much more stringent annealing process that complex alloys require, making it harder to do a poor annealing job. I've got no proof of this, however.

For what it's worth, I've drilled a whole lot of holes with HSS and ti-nitride bits. If, for some reason, you can't get your hole drilled with them, in my opinion you should just use carbide. A sharp HSS bit is more than enough to drill annealed steel, even poorly annealed steel.
 
AcridSaint said:
For what it's worth, I've drilled a whole lot of holes with HSS and ti-nitride bits. If, for some reason, you can't get your hole drilled with them, in my opinion you should just use carbide. A sharp HSS bit is more than enough to drill annealed steel, even poorly annealed steel.
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That is what I thought, but after what Nathan said and from your comment makes me wonder if either I am not doing it correctly for some reason or that somehow I am causing the steel to harden with my drilling of the first hole. Or a combination of both.
 
I have to admit that I don't manually drill holes very often anymore. So as an experiment, I just went out to my shop and dug around some and set up some drilling experiments. I used two drill bits, one a cheep "Craftsman" drill bit, HSS, and the other a production quality, no-name "made in USA" cobalt with a really thick web.

My "drill press" was set for 1100 RPM, so I left it there. I also didn't use coolant or oil of any kind. I setup a big nasty chunk of 1018 CRS in a vice, that has proven itself to have hard spots in it (2" X 3" cross section, for some reason the thick stuff is worse about hard spots). Both drills made short work of turning it into swiss cheese. I set the quill stop to 1/4". I drilled a bunch of holes, 3 to 4 seconds per hole, 1/4" deep. No problem.

I then went to my knife grinder and ground the tips off, and resharpened them free hand on a clapped out 120 grit belt. It took me two attempts with the thick web bit because it requires a split point due to the web thickness, which took me two tries. Time to completely resharpen a bit? About 20 seconds. The bits tend to walk a little bit after resharpening because of an imprecise web, and I'm sure the hole isn't quite as perfect. But both bits drilled without problem.

Next challenge: 3/8" 6-6 titanium (6-4's big brother). 180KSI yield point, high hardness titanium. Just for grins I left the RPM at 1,100, and attempted to drill without pecking. I would normally run this at 600 RPM, and use coolant, but just for grins. The bit goes halfway through, then the tip glows and cutting stops. Both bits are this way. So I repoint them (about 30 second total) and do it again with pecking to allow the bit to cool. Both bits can get through 3/8" 6-6 ti in about 10 - 15 seconds. I put it in back gear which drops the RPM by 90% and can drill them without pecking. I made swiss cheese out of that titanium in a couple minutes

While I was out there, I tried a carbide tip concrete bit. I don't know the brand, but it was made in Germany. It made a dimple and stopped cutting. Pure junk for this.

I'm not turning real slow. I'm not using oil. I'm feeding hard and letting off as the bit starts to exit. I'm not letting the bit sit there and rub or squeal or chatter.

There is no reason a knifemaker using a decent quality drill should have any problems at all drilling dozens of holes in unhardened steel with a regular HSS or cobalt HSS, drill bit. Feed harder - peck or use coolant if it is getting hot (blue chips) - let off when it starts to exit. If you are drilling a large hole, drill a smaller pilot hole the size of your web first.
 
I'll have to try some masonary and cobalt drills from MSC. I've broke 2 solid carbide and 1 carbide tipped drill already on A2 steel.

Will the HF HSS Titanium Nitride Drill Bits work good for micarta handles?
 
They'll work fine on micarta/G10 etc. Carbon fiber will wear them down, but it will do that to quality bits also.
 
In addition to proper feeding which has already been mentioned, you may want to look at the RPM you are running your drill at.

The formula I always used for finding the RPM to drill at is CSx4/D
CS is the cutting speed of the material you are drilling into. For mild steel it is 100, for high carbon it is around 50.
D is the diameter of the bit you are using.

So a 1/2" drill bit would be (50x4=200, 200/.5=400) 400 RPM.
For a 1/4" drill it would be (50x4=200, 200/.25=800) 800 RPM.
 
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Thanks guys I really appreciate the advice. Thanks Nathan for all of the testing. I guess I was just babing the bits to much and ruining them and making the steel even harder. It acutally makes sense to me now. I will do the next set and bear down on them a little harder and see how much better they do. It just seemed that these would start screaming just a few seconds after I started drilling with them. Just goes to prove that you are never to old to learn something. Thanks again.
 
10xx steels need to be annealed before you attempt drilling. There is a thing with the carbides being in layers that one of our more educated forumites could explain better.

A technique I learned is to back the drill out of the hole as soon as it starts to raise a swalle/chip. This gets the chip out of the hole where it creates more friction, and allows the bit and work piece to cool off. Also add oil a few times on each hole.
 
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