Drilling Big Holes in metal, that is, Holes Bigger Than 1/2" Diameter

Several ideas for drilling larger holes by hand without harming yourself

Last Revised: October 19, 2023

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Back in 1996, I wrote to the "third hand" column of the Home Shop Machinist magazine explaining the difficulties I had in drilling 5/8" holes out to 3/4" while I was working upside down under my Case Tractor. Within 2 weeks after that issue got to me I had 5 replies!
Some of the guys had more than one idea. Many of them recounted problems they had had, or horror stories about others. Later, I received both phone calls and letters. Since I had not published my address as part of the article, all of these guys had trouble getting to me. fortunately I live I a small town, so I did receive 3 letters with only my name and city/state in the address and one more forwarded to me by HSM. One guy used the Internet to get my phone number.

I do want to note that I am not personally recommending any of these ideas, since you, the user, needs to evaluate them for safety and viability.

It is amazing to me to see so many different solutions to this problem. There is something in here for everyone who might ever be faced with this need.

Here are the basics of each idea:

Start with a small pilot hole, open it up to about 3/8".
Then, grind the rake angle of the full size drill bit to Zero degrees (or even a bit negative). This idea works because the drill bit's web is not engaged in the metal since the pilot hole has provided clearance and the zero rake keeps the big bit from digging in.

Use a magnetic base drill.
Attach a flat plate to the work first if needed.

Use a high speed steel hole saw.
Drill a 1/4" pilot hole first and replace the drill bit in the hole saw with a solid 1/4" pin to provide accurate centering.

Use 3 or 4 flute core drills to open up smaller pilot holes.
The core drills don't catch and dig like 2 flute twist drills.

Use tapered bridge reamers to progressively open up the hole to the finished size.

Rudy Kouhoupt, HSM contributing editor
Use the Cole Drill, which is the hand powered drilling machine described in the Machinist's third Bedside reader.
He said: "I can identify with this one since as a blacksmith of some skill, I like using the blacksmith's Post Drill which is also hand powered."

Start with a small pilot drill , say 1/8th, then move up by eighths.
Use DoAll cutting wax (which holds better than oil).

Rent or buy a right angle drill.
This design will lessen the difficulty of alignment and reduce the effects of twisting. when the drill bit hangs up.

If you have a bench size drill press, turn the head upside down
and locate it under the machine that needs the holes drilled. (He had to drill holes under a tractor, just as I had to).

After telling one particularly serious horror story, Lee said that the guy finished the hole with a die grinder and vowed to never drill a hole bigger than 3/8" for the rest of his life!

Use a "Third Arm", a long wooden stick, through the handle of the drill motor.
Attach the handle to an immovable post. The idea here is to poke one end of a 2 1/2 foot long wooden handle through the D handle of a large drill motor to keep the drill motor from twisting. The other end of the long handle is notched and pinned to a heavy steel bar which is anchored to the piece to be drilled or wedged into a handy location.

Press drill bushings into a sizable plate and clamp the plate in place over the site of the hole to be.
The drill bushing will help keep the drill straight and reduce binding. Work up to the final size in several increments.

Keyless Chucks vs. Drill bits with 3 flats:

The Question:
Seems like most drills nowdays come with keyless chucks and my old arthritic hands have a hard time getting them tight enough to hold a round shank bit in some situations.
I was wondering if anyone has a slick method or jig idea to put 3 flats on a bit shank?
The tools I have available are hand grinder, bench grinder, magnetic base surface grinder, metal lathe, and misc hand tools, no mill.
I've had limited success eyeballing them on a bench grinder but there has to be a better way.
Any ideas appreciated.

Pete's Answer:
I'd go with the lathe, which probably DOES have a spindle indexing system. If not, you could make a stop to locate the 3 jaw chuck at the proper intervals.
Then use a file, held level to make the flats. Measure from the flat to the opposite side of the shank so all 3 flats are the same thickness.


Jeweler's have a neat little U-shaped rest that assures a repeatable filing plane.
Here's one example:
Jeweler's Filing Rest

I think you get the idea from the above.

One caveat when using a drill bit with 3 flats:
About a year ago, while working on fancy blacksmithed hinges for a pair of large doors, two of the guys came to me asking me to put flats on a 5/8" drill bit because they couldn't get it to chuck up tight enough while opening out several holes. I did as they asked and they went away. Later, one of them told me that he almost broke his wrist when the drill caught in the hole, using a very powerful drill motor.
The drill bit, of course did NOT slip in the chuck.