Drilling 1/16 holes

Cooker, I've drilled many a 1/16" hole through steel at far less than the "optimum" rpm, although admittedtly not an inch thick. I keep my drill press on the lowest speed setting for more "average" work and don't even bother to change it when I have to drill a small hole like that. Is it optimum? Of course not, but it works well enough unless you are in real a production situation. My recommendation is to make sure your drill is sharp, make sure your alignment doesn't shift on you, use plenty of lubricant and proceed at a slow pace, withdrawing the drill often to help clear chips. Don't apply a high force to the spindle - go easy. Small drills like that are hard to sharpen so you might want to start out with a new high speed steel drill - they're cheap enough individually. Even if you go through a couple of drills to get the job done, it certainly is doable, IMO.

Rod

I went for many years running the drill press at whatever speed it was set at, no matter what size the drill bit or what the material, holding the work by hand, and pushing down hard no matter how small or large the bit. I then found a 1942 booklet put out for the war effort by Cleveland drill company "Handbook for Drillers". I read a bit about proper drilling speeds and feeds and how to properly mount your work on a vise or clamp it to the table. Funny enough, when I started using those spindle speeds and proper feeds, and began solidly clamping the work, I no longer broke bits. My holes came out clean and accurate, no squashed out metal on the bottom, no wandering bits, no grabbing. Try it.

It also told how to properly sharpen drill bits, how to tell a bad sharpening job, how to handle brass and aluminum, how to handle extremely hard materials and even how to look at a bit that failed and figure what caused the failure. I think Lindsay has this book. Worth its weight in gold.

Too slow a speed will result in a poor surface finish in all cases and, in the case of drilling, a tendency for the bit to grab as it sort of rubs and then suddenly digs in.

Key point I gleaned from a manufacturing process book I picked up the thrift store years ago, "...finish will improve with increased speed until the tool fails due to heat." I had a guy at work trying to cut a seal surface on a welded up bushhog shaft in our huge Pacemaker lathe. He was running at 20 rpms and the tool was just tearing metal off, leaving an awfully rough finish. I walked over and threw the machine speed up to about 300rpms. "I'm trying to be very careful," he protested. I explained that spindle speed had nothing to do with being careful and that he was never going to get a slick enough finish at such a low speed. He finished the work in about three minutes and it was perfectly slick.

There are three basic factors that determine how a piece of metal cuts. Hardness, depth of cut, and surface speed. Increase any one and more heat is generated. So if the metal is extremely hard, you have to slow down and feed very lightly. If the metal is fairly soft, you can feed heavily, but you may need to back the speed down if you really get on it. If you run the spindle fast, you will have to back off the feed a bit, but the cut will still go very fast and the finish wil be good. The trick is to find the ideal balance that doesn't burn the bit up, doesn't wring the bit off and that allows you to do the work relatively quickly.

The sharpness of your tool is also a factor that regulates speed and heat. Dull bits generate more heat, so they dull faster, so they generate more heat, so they dull even faster, etc.... in an every tightening spiral until it either burns totally up or wrings off. Nothing will demonstrate this effect like putting an even slightly dull drill bit to titanium.

Make sure the stock is clamped tightly, and if you even suspect that the drill is becoming dull, change it.

The easy way that it was taught to me is that you want the outer edge of the bit spinning at the same speed regardless of the diameter. The farther it is from the center the faster it goes. Therefore a big bit uses a slow speed and a small bit uses a high speed.

But seriously, follow the guys who are telling you to drown it with oil (air works too, but oil is better) You gotta have an extremely light feel on the feed lever, and peck it ever so gently.

One huge reason a small bit can't plunge like a bigger one, is because the % of flute vs.web is much lower. The web has to be thicker so the drill has some strength(also gets thicker towards the top in all drills). In say a 1 1/2" drill, the web will be MUCH smaller than the flutes. Now look at your drill. The web takes up atleast 1/2 the diamter of the drill, leaving very little room for chip evacuation. Basically, they plug up MUCH quicker and therefore should be pecked (very shallow for small diameters) instead of straight plunge feeding.
Donovan from Wisconsin

Going by memory , cutting speed for mild steel is 80-120 sfm.

If you go on the low side then 4 x 80 diveded by .0625 = 5120 rpm .

One important thing is to not let the flutes of the drill pack up with chips in the hole. That will break a drill in a hurry.

1. Go SLOW, the slower the better.

2. Use too much oil.

3. Like they say, clean the hole often, real often.

4. Take your time.

5. Center punch your hole.

6. Buy more bits, two per hole perhaps.

7. Like I said, take your time and go S-L-O-W.

Good luck and let us know how you did.

cutting speed is determined by the metal, mild carbon steel would be 60-80

Assuming your steel fpm is 60 it would be 12 X 60 = 720
pi x dia (in your case 1/16) = .0625 x 3.1416 = .19635

720/.19635 = 3666.9 rpm.

So I would say you arnt drilling near fast enough, and the softer the metal the more grabing. Cutting oil will help but wont necessary eliminate the need for speed.

To keep from breaking the small bits, you need to reduce down pressure on the bit, increase the speed, you can use cutting oil and or air to keep the bit from burning up.

your milage may very

A 1/2" bit should be running at 500rpm for the proper speed to drill in steel. 1/4" should thus be 1000rpm, 1/8 should be 2000 and thus a 1/16" bit should be running about 4000rpm top achieve the proper surface speed. As you can see, there's NO WAY 1300rpm is too FAST. Most drill presses cannot run fast enough to drill 1/16" holes at the proper speed so the bit grabs and wrings off, which is exactly what happened to you.

You were feeding too hard. I know you barely had any pressure on it, but at only 1300rpms, it was just way too much. This is two-fingertip feed pressure at most and even then I would drill about 1/16" at a time and then back out to clear the bit.

K-Mo

I think K-Mo hit the nail on the head for breaking the bit. I can see myself adding just a touch of too much down pressure just as the hole fills with chips, and snap, time for another bit.

T_Bone