How to drill holes in mild steel: 1/2" up to 1 1/4" or so?

[anickode]

If you're using a hand drill, you're going to have issues no matter what bit or cutter you use. A good quality set of hole saws and a beefy low speed drill (600 RPM or less, and not a Ryobi cordless or anything like that), combined with a spray bottle of water based cutting lube will yield the best results from a handheld setup on anything 1/8" or thicker.

My #1 favorite for anything thicker than 7ga (about 3/16") is a mag drill with an annular cutter, but that setup will cost around a grand on the cheap end.

Anything from Klein tools or greenlee or anything of the electrical tool companies will mostly be sized for electrical knockouts, and not your common fractional sizes. They will usually skip any size that isn't commonly used for electrical work.

Remember, when working on steel, slow and cool is the way to go. It's really easy to overheat tooling, which will ruin the heat treat and render it worthless.

 

[Kartorbust]

Drill or cut slow enough and you won't need cutting fluid. However machinists have bickered back and forth for years whether or not cutting fluid is needed and the affect it has on the tooling. I don't want to go down that rabbit hole, just wanted to give both sides. My metallurgy instructor in college took machining and he's stated it doesn't help anything out. It's only used because machinists are too impatient to slow down.

 

[OzFab]

Drill or cut slow enough and you won't need cutting fluid.

Sorry but, I beg to differ; when I picked up my new lathe, I also bought a bottle of cutting fluid & I have noticed a vast difference, especially with the hole saws...

My metallurgy instructor in college took machining and he's stated it doesn't help anything out. It's only used because machinists are too impatient to slow down.

A metallurgist is to a machinist as an engineer is to a mechanic; for the most part, the former is a theorist where the latter is 100% practical & there's not usually a lot of cross-over; as I mentioned, I've personally seen what not using lubricant can do...

The tool in the pic below is now all but useless because both ends have been overheated; no, they weren't run especially hard or fast, just dry...

FYI: For this application, WD40 is a lubricant...

 

[Nosandwich]

WD-40 is a water displacement product. The fact it works as a "lubricant " in this application, is because it is, in fact, a pretty poor one.

Water is cheaper. Throw in a little dish soap....

 

[Kartorbust]

Guess that's what I get for paying for college classes

 

[Nosandwich]

Guess that's what I get for paying for college classes

Money well spent?

 

[anickode]

Guess that's what I get for paying for college classes

I'm with OZ. Experience has proven that even sparing use of lubricant extends the lifespan of tooling, particularly with twist drills. Proper technique is critical as well, but the combination of the two definitely yields the best results.

 

[zogthegreat]

FYI: For this application, WD40 is a lubricant...

LOL, this is probably the only practical application that I have found for WD-40. IMO, it's crap compared to other rust penetrating oils, but it's nice for cooling and lubricating bi-metal bits. I've noticed that the bit cuts better and quicker when using some type of lubricant. If I don't have WD-40, I use transmission fluid in a spray bottle. In a pinch I've used 5w-30 motor oil. I also use it when I'm cutting mild steel with a jig saw. The blades unquestionably last longer and are less prone to break.

 

[anickode]

LOL, this is probably the only practical application that I have found for WD-40. IMO, it's crap compared to other rust penetrating oils, but it's nice for cooling and lubricating bi-metal bits. I've noticed that the bit cuts better and quicker when using some type of lubricant. If I don't have WD-40, I use transmission fluid in a spray bottle. In a pinch I've used 5w-30 motor oil. I also use it when I'm cutting mild steel with a jig saw. The blades unquestionably last longer and are less prone to break.

My personal favorite for stuff like that, along with drilling and thread cutting is Tri-Flow. It's not as cheap as WD40, but it works way better, and a little goes a long way. It clings to tooling and materials better than most other "everyday" lubricants, and it actually has a pretty pleasant smell when it starts to warm up.

 

[zogthegreat]

My personal favorite for stuff like that, along with drilling and thread cutting is Tri-Flow.

Where do you get it? I have some cutting and drilling coming up for a project!

 

[anickode]

Where do you get it? I have some cutting and drilling coming up for a project!

I just get it at my local Ace hardware. Comes in small squeeze bottles and full size aerosol.

 

[Blackdog]

Thanks. I was looking at step bits and the graduations seem to be about 1/8"...so not good for 3/16" stock. I guess I'll just buy 1/2", 5/8", 3/4", 1" twist drill bits.

 

[anickode]

Thanks. I was looking at step bits and the graduations seem to be about 1/8"...so not good for 3/16" stock. I guess I'll just buy 1/2", 5/8", 3/4", 1" twist drill bits.

Step bits are really only meant for sheet metal. I wouldn't use one in anything thicker than about 14ga. You never want more than one step cutting at a time. The problem with step bits is once you cook one step, every step larger than that one is useless.

A good set of hole saws is a good investment. Once you buy a good set with locking mandrels, you can replace the individual cutters as you wear them out. Even a good set of bi-metal hole saws will be functional in steel and last you a good while, as long as you take care of them.

Large diameter twist drills (silver and Deming bits are stepped down to 1/2" shank for use in smaller chucks) can be dangerous and easy to ruin in hand drills. The problems tend to arise when you are drilling metal that is thinner than the beveled top of the bit, so the tip is punching through the back before the cutting edge has fully engaged with the material. As you advance on the cut, the bit will eventually break through and not complete the cut, leaving two lobes of metal attached. The bit will then act as a screw and suck in faster than you can possibly react. Removing those two lobes using the bit can easily lead to a damaged bit or damaged drill.

I prefer not to use a hand drill with twist bits larger in diameter than the Chuck capacity. I have done it, but your average hand drill won't last long with repeated use.