Technical Shop Class Basics: How to Properly Drill a Hole in Metal

It dawned on me today in my shop that no machinist ever instructed me on how to properly drill a hole in metal. So, please, speak up with the assumption that most of us have been doing this basic operation in an incorrect manner.

A couple questions:

What are the best drills for general shop use for a wide variety of jobs?
How is the proper way to keep drills sharp? Is there a sharpening tool or procedure you recommend?
When is it necessary/desirable to drill a pilot hole?
To lube or not to lube? With wax? With cutting oil? Used motor oil? 3-in-1?
High speed or low speed? In my shop I have a 3/8ths variable and a 1/2" single speed press
Once drilling, put your full weight into the job, bearing down hard on the drill? Or light steady pressure?
How to get a clean hole on the back of the metal?

I am sure I have left out some points. You machinists likely take it for granted that the rest of us hobbiest know what we are doing. We don't. No time like the present, however, to enroll in shop class on the HAMB.

Thanks guys for the instruction here. I know you all to be excellent teachers.

Pete

 

Here's a good start re: metal drill bit selection. Avoid drill bits made of just High Carbon Steel. Ok for wood, not metal. If you can afford it buy, a set of High Speed Steel (HSS) Fraction Drills, Letter drills and Number drills.

Always drill a small pilot hole (1/8") so drill won't wonder off center For most accuracy use a prick punch and then a center punch to mark the hole's center.. The pilot hole should be smaller than the wed thickness of the drill. Then step drill for accuracy and ease of drilling. Also ensures the hole will be round, not oval.

Use oil on steel WD-40 on non- ferrous.

That's enough for now. Others will chime in. Remember, everybody's an expert!

 

Is this YouTube video on the money? Proper way to start? According to this video, I have been drilling holes entirely wrong. Sheesh....

 

And here on sharpening drill bits by hand:

 

In the video, "This tool here." is a combination square.
You only push down on the drill enough to keep forming a chip.
He is applying too much pressure and almost punches thru the hole with the drill bit.
I bet he breaks a lot of drill bits doing this. If you do this with a larger drill bit (1/2 in and up)
the drill bit will jam as it tries to break thru and may break. You wrist will also get "torqued".

 

a "Drill-Doctor" is a good investment, especially for a beginner(& some of us old Farts that can't see so well anymore), especially if we read the manual & learn how it works. They are available up to 3/4"capacity, & do a good job of keeping your drills in shape. When a drill gets dull, it won't cut properly & may wander or break. Another tip : for a clean good looking hole, after you've drilled it, take a countersink & LIGHTLY touch-up both ends of the hole to remove the slight burr from the drilling. Keeps you from getting cut on the burr or having it keep your bolt from tightening properly & makes your work look more professional.

 

I used to hire an older man that was retired to work for me temporarily, I would have worked him all year round but he would only work for about three months at a time. The first thing I would have him do is go through the drill bits and sharpen them. He could put an edge on them far better than Drill Dr could. He just pulled a stool up to the bench grinder and had at it.
I asked one time how he did it and he just looked at me and smiled.

 

Here is the instruction video. Looks simple enough to use. Thank you for the suggestion.

https://www.drilldoctor.com/how-to-videos

 

The larger the drill diameter, the slower the RPM's. Speed kills drills.

 

My teacher in high school shop class told us that a drill will only take off so many cubic inches of material per hour. A small drill needs a higher speed to take off as much as the big drill in the hour. There were charts we were supposed to use to get the correct speed.
He also taught us how to sharpen drills. I never really got the hang of it.

 

I have found when drilling holes in sheet metal, and I do not have a step drill- a center drill works great. Dad taught me this 60 years ago.

 

Cleveland twist drill made a booklet years ago. It is very helpful. I 'm sure anybody can find it, if they are willing to search. When I was an apprentice, we were taught you can drill anything at just about any speed, as long as it has the right feed. Rebuttals begin.

 

When cutting stainless steel or other hard metals I use a wide angle drill 135* as the load is spread out and won't dull the point meets diameter corner of the drill. Cutting oil for steels, motor oil will work, kerosene for aluminum.

I always use a center drill to start, it has a small point and won't walk like a regular drill bit. Small diameter drills, run fast, slower as you increase in diameter.
Remember to clean the chips out of the bit, otherwise it will stop cutting, heat up the work piece, then break.

Good info here: https://www.practicalmachinist.com

 

phartman's video is excellent. If you want to sharpen your own drills
buy a drill point gauge to measure the angle and length of the cutting lips. Easier and more accurate than a ruler.
Small dia. drills (less than an 1/8 in.) are more difficult to sharpen by hand than larger drills.
https://www.amazon.com/s?k=drill+point+gauge&ref=nb_sb_noss_2

One way of getting a clean hole on the back side of the metal is to drill from top side but don't break through. Then flip the piece over and drill from the bottom side. Of course, this is not always possible on big pieces, takes more time and sacrifices accuracy as you have to re-clamp your work. OK for non-critical holes.

Finally, wear safety glasses, have short hair and make sure your work is clamped tightly in a vise or using hold downs on a drill press table. Never use your hand as a vise.You may get by once or twice but,eventually you will get injured. Just imagine what a piece of sheet metal can do to your hand when you lose your grip as the drill bit breaks thru.

 

Damn I ruined a couple bits yesterday just before coming home and reading this. Tendency with a variable speed hand drill is to floor it.. So are overheated bits still sharpenable?

 

I feel your pain. Same question started this whole thread. I really don't know beans about such a simple operation. Lots to learn here.

 

The worst thing for drill bits is the new guy. bits are one time use only. even mag drill bits.

companies buy those Milwaukee drills from Home Depot constantly. they are way too fast and twist your arms up when they bind. I drilled 48 holes in angle iron one day with one pilot bit, one unibit, and cutting oil, with a drill made in the 50's that is super slow. yeah make fun of me for using old tools.

 

I always used a bit of regular motor oil when drilling for most of my life, but recently bought a bottle of cutting oil. I don't know what the difference is, but I think it works better.

I also like my Drill Doctor. Every once in a while I'll get one that doesn't "take", but it was probably ground uneven by me because the bit was chipped on one side. It usually provides a great result.

I always drill a pilot hole. Unless the final hole is about 3/16" or less. A good center punch really helps, even if you have your part clamped to the drill press.

I've come to love Unibits for use on sheet metal.

 

For any sheet metal , steel or aluminum, its best to use a "Uni-bit" step drill. Since they are a single flute, the rest of the body supports the hole being cut and the next step can be used for de-burring the hole. Using a twist drill in sheetmetal will often times cut a tri-angle hole.
The good ones are not cheap, but if you take care of them will last many years

Also for regular drilling of all other metals, consider using "Jobber" length. They are half the size of a normal drill and do not wander.

 

. . . Great Thread . . . Thanks . . .

 

Gosh, I taught industrial high school metal shop for 33 years and then in 2006 it was closed.
Glad my students had the chance to learn lifelong skills that can't be taught by watching a computer screen.
Kids today are definitely missing out.

 

Funny, I was a safe machinist for 30 years with long hair. Common sense and a pony tail down your shirt helps out and no, you don't need short hair to machine. I managed to be in charge of third shift, so I must have been doing something right.

 

True but there are those folks who "forget". Kind of like getting your shirt tail
caught in the lead screw of a lathe or leaving the chuck key in the lathe chuck.
Glad you stayed safe and sound.

 

Belt sander is the thing to sharpen bits on. Start it on the 'back side' and roll it up to the front cutting edge. If you sharpen one side more than the other you can see the spiral cuttings from just the one side and it won't drill straight, tossit when that happens.

 

Not just the new guys, the forgetful guys. And I was using a new Milwaukee...

The problem I had, and often run into, is being under a car, drilling though a frame with hardly enough room to fit the drill, let alone get adequate pressure with the one hand that fits in there. At the same time trying to manipulate the variable speed trigger. If they make some kind of hand drill clamp/jig that helps I'm all for it.

 

There are a lot of variations to "how to properly drill a hole". A lot depends on the precision you need as far as the size and location of a hole. When you drill a hole in most anything its best to start with a center punch or a center drill. to maintain location. A center drill is a stubby drill with a bigger body and a smaller point on the tip. Machinists normally use these to locate holes. Then drill a pilot hole with a small bit. It seems that there are times when using several drill sizes to work up to the finished size works best. Yet there are other times when fewer sizes work best. Isay this because as you get to larger sizes with only a small amount of metal being removed, there is a tendancy for the bit to make a large chip and grab the drill...especially when breaking thru the other side of the metal. You see this less when you have the leverage of a drill press. When working with a hand drill, the resultant grab by the chip can be painful. I have an old gear reduction drill that will wrap your arms around each other. Some of the newer "brushless" drills are small but they can surprise you too. You kinda need to develop a feel for what the bit is doing, especially when it begins to break thru the other side of the part. Generally the larger the bit, the slower speed you use. Its ok to kinda pump the drill trigger to get real slow. Too much speed dulls bits quickly. If you want a round hole, there are ways to do it, but a two flute drill tends not to make real round holes...especially on thin steel. There are "core" drills and reamers that are made for finishing holes to rounder shapes and precision sizes. Drill your hole slightly undersize and then ream it or use a "core" drill. Obviously you will only need to do that when you are making something that requires some precision. The best thing I can say is to pay attention to the feel of what you are doing whether on a drill press or by hand. As an experiment, take a piece of thin sheet metal and drill a hole with a 1/2" bit and see how round it is. When a bit rubs while drilling (too much speed/too little pressure) it can work harden the metal and you can't figure why the bit quit drilling. I have found that if you take a cobalt/carbide air tool and grind slightly you can remove the work hardened area and then continue drilling. As I mentioned, it has a lot to do with developing a feel rather than just pushing as hard as you can. Try drilling two holes thru some thicker metal. Hand Drill one 1/2" and one 3/8".
Now take a 5/8 drill and try to finish drill each of those two holes. Often you will find the one removing the least metal will tend to grab more than the one removing more metal. You don't want too much metal but too little can be a problem also. Not sayin it will happen every time, but just think about it when you are having problems with grabbing and breaking drills. Don't waste your money buying the gold coated drills at Harbor Freight....waste of money. I have had decent results with HF Cobalt drills. Just catch them when they have the blue tag and use the 20% coupons. I think you end up paying about $70/$80 then. Their "Demling" drills will do a decent job on larger
holes for the price...just watch the video that was posted above on "Drill Sharpening".

 

You might want to check out the drill that HF sells for tight spaces. For the price its handy for those occassional tight spots. You can also get air drills that are very compact. There are cheap ones and expensive ones, but they all are handy when you are in a tight spot.

 

Ok. Now it's time to learn how to true and dress a grinding wheel prior to drill bit sharpening.
You Tube videos are available.
Not trying to start a war but sharpening drills on a belt sander is a last resort, only if
you don't have a good grinding wheel.

 

Did that once......only once!

 

Drill point angle, Drill point angle, speed. Speed kills.
not everyone has a hardness tester, a good tip is strike the material with a file.
Generically the answer is hard shit is 135 and soft material is 118