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.
- 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
Step 1: Tools
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
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
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!
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.