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Prepare to Drill Metal : How to Use a Center Punch

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Picture of Prepare to Drill Metal : How to Use a Center Punch
This is one of those 101 topics that I feel could use some exposition so drilling holes in metal can be a confident, well-informed, and efficient experience.

A center punch is a tool with a pointed end that makes a dimple in your piece of material right where you intend to drill a hole. 

A center punch mark accomplishes two things:

- It gives a physical resting place for a drill bit so it stays right where you want your hole to be
- When you begin drilling, the recess of the dimple relieves pressure from the flat tip of the bit (the "chisel tip" or the "web".) This prevents bending, chipping, breaking.

PLEASE:

- Consider center punching a REQUIREMENT for making holes in metal with drill bits
- Use a center punch for bits up to (arguably including) 1/2" in diameter.

For larger bits ( > 1/2"):
          - make a center punch
          - drill with a bit the size of your intended bit's chisel tip (this is called a "pilot hole")
          - drill with your intended bit.

For this demonstration, I'm drilling a hole in a piece of mild ("hardware store") steel. Well, in the interest of full disclosure, I'm making a corner bracket. :)

And, naturally, I did all deez workins at Techshop Detroit! www.techshop.ws
 
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Step 1: Tools

Picture of Tools
Pictured here are my preferred tools for making center punch marks in metal.

L to R:

- Ball peen hammer
- Solid steel center punch

You may be familiar with the "hammerless", spring-loaded centerpunches. I don't generally like to use them with metal because you can't control the force of the blow - the spring exerts the same force every time - and because if/when the spring breaks, it's useless. I don't mind them for softer materials like wood... But this is how I like to get the job done.

A Ball peen hammer (notice the ball "peen" or face to the left) is a good all-purpose hammer for a metal shop. You're going to use the flat face to make blows on your center punch, which will inevitably mark up the face. Those marks will transfer to whatever softer material you hammer next so... dedicate this hammer for general mashing/banging/tool-hitting purposes. 

Step 2: Mark Your Material

Picture of Mark Your Material
A center punch has a fine point so it can get you great accuracy! Making a good center punch mark means you can be sure your hole will drill nicely before you've even drilled it.

Therefore:

Measure and mark as accurately as you require!

* A criticism of the example below is that those pen marks are very wide! I could make a sharper, more accurate mark with a scribe.

Step 3: Center Punchin' I : Choose Your Surface

Picture of Center Punchin' I : Choose Your Surface
So now we come to the Main Course. You'll see that this is a simple operation overall but it gets you thinking about how to use your tools well.

Find a strong surface to support your metal while you punch it. I used the anvil on a table vise; a normal anvil will do, as will a bench block (flat table-top anvil) or a sturdy, steel-topped table. I'd certainly get the job done working on a wooden bench, a stump, or even the shop floor, but this is a good habit to start:

"When you're looking to compress your material, support it with steel!"

For this process, "compressing" is driving the center punch into steel to make a ding. The hard steel anvil keeps the force of the blow right where you want it - in your material. Softer supports like stumps and hardwood stakes are good for forming material.

Keep all this in mind next time you go to strike a tool on steel [using a ball peen hammer]!

Step 4: Center Punchin' II : Do It!

Picture of Center Punchin' II : Do It!
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Grab your hammer. Hold it low on the handle and WRAP YOUR THUMB AROUND! It's like you're making a fist but the hammer handle got in the middle.

Don't grip too tightly. The object here is for the hammer head to kind of "fall" straight down onto your work. Yep, I do mean even with a light blow. This hammering method is very accurate (the head falls nearly straight down from gravity) and the relaxed grip is much easier on your elbows in the long run. You can use this technique for all kinds of hammering.

So, like I was saying... Grab your hammer, touch the center punch point to your mark, and hold the tool straight up and down as you give the tool a good, solid blow. Tools tend to jump with rapid blows, so best to get a solid punch on the first try.

"My mark is a smidge off!" This is a tricky one, getting a new, functional punch mark *just this side* of an old one is unlikely. Chances are, the project you're working on will forgive a hole that's very slightly off. Using the off mark to make a small pilot hole and then finessing the larger bit over might repair some of it. But truth be told, if you need ultra accuracy, consider using a mill.

Step 5: Voila!

Picture of Voila!
Center punch mark accomplished. Ready to register your bit in a drill press and make the cut entry better for your tools.
padbravo9 days ago

Great picture! good closeup.

Pizzapie5002 years ago
Hehehe, I use an auto center punch :D

What is that thing?

enl_public11 months ago
re: "my mark is a smidge off"

The punch mark can be walked along the surface by tilting the punch. Light blow for the mark, walk it to the correct location with light blows if it is off, THEN heavier blow for full punch mark.
tholopotami2 years ago
Nice! Whoever has done even a little metal work knows that the preparation for drilling is not a trivial matter.

This is a trick I use which I learned from others and involves a hand (motorless) drill . Suppose the mark of your centre punch was a little off.. Then using the hand drill at a small declination from the vertical direction you work trying to shift the mark to the desired place pressing as you turn the tool. If you use the appropriate bit size the mark should be round and centred again.
embochner2 years ago
very informative thanks
rimar20002 years ago
Nice instructable.

When you need to make a hole of 1/4" or more whit a little accuracy, you can make before a littler hole, i.e. 1/8", obviously in the same place. That simple trick make easier to do the entire work. That is named "pilot" hole.
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