Center punches are commonly used in drilling applications. Why are they necessary in drilling applications, and how do they work? This article unpacks these questions.
What is a Center Punch?
A center punch is a hand tool used to make a slight indentation in a workpiece as a guide for the drill bit. This allows the drill bit to start cutting the hole at this precise location without slipping, ensuring accurate hole placement.
The point angle of a center punch is 90 degrees. The punching tool with a 60-degree angle is called a dot punch.
What is a Center Punch Used For?
When using a non-self-starting drill bit to start drilling a hole in any workpiece, the drill bit tends to wander in all directions. This causes inaccurate drill placement and sloppy drilling. Using a center punch fixes this problem.
A center punch is used to create a tiny indentation exactly where you want to place the drill hole, allowing the drill bit to grip the material without slipping or wandering. Here, you have neat and precise hole placement, ensuring accurate work. While using the center punch adds an extra step to drilling operations, it ensures safe, neat work.
Wandering drill bits cause more than just sloppy workmanship. In some cases, wandering drill bits can snap, causing injuries and damaging the workpiece and equipment. Using a center punch eliminates this risk.
Types of Center Punches
There are two types of center punches: manual and automatic.
1. Manual
Manual center punches require using a hammer in conjunction with the center punch. Here, the force that creates the starter hole or indentation comes from striking the punch using the hammer.
The manual center punch tool is usually made out of mild steel or tool steel. It is then hardened and tempered at the tip while keeping the head is kept soft to withstand the hammer strikes.
2. Automatic
Spring actuated automatic center punches eliminate the need for a hammer.
The automatic center punch has a spring-loaded hammering mechanism inside. You place the sharp tip at the location you want to drill and push the shaft of the center punch down with your palm. After a certain distance, the spring inside the punch’s shaft is released, striking the sharp pin into the workpiece. The force with which this hardened pin strikes the workpiece creates the indentation.
How to Use a Center Punch?
Before using the center punch, some preparation is required. Measure out and mark the exact drill hole placement. It’s best to mark this in a clear X, with the hole location where the two lines intersect.
Place the center punch tip on the X with the body of the punch perpendicular to the material. Placing the center punch could be tricky since you can’t always see the tip, especially when viewing it from the top. To ensure correct placement, place the tip along with one of the lines of the X, slant it slightly, and slide it towards the intersection. Once the tip reaches this spot, straighten the punch’s body perpendicular to the workpiece.
Once the tip is in place, it’s essential to ensure that the punch’s shaft is perpendicular to the workpiece. It could slip if you let it slant, creating a line instead of a dot. This would cause the drill bit to slip, negating the purpose of using a center punch.
Using a Manual Center Punch
If you’re using a manual center punch, lightly tap the back of the punch using a hammer. This creates a neat indentation in the workpiece where you can start drilling. If you’re new to using a center punch, give one light tap with the hammer, then check that the indentation is correctly positioned. If the position should be readjusted, repeat the tip placement step.
Ensure that the hammer connects with the back of the center punch in a perfectly vertical position. This directs all the force applied straight down into the workpiece, ensuring maximum efficiency and avoiding inaccuracies.
Once you’re satisfied with the positioning, place the punch’s tip in the indentation you just created. Ensure that the shaft is upright, then use the hammer to tap it harder than before. This will deepen the indentation. Repeat this until the indentation reaches the desired depth. Soft material would require one firm tap from a hammer to create the desired indentation. In contrast, hard material may need up to three hard taps.
If you’re finding it hard to create an indentation with sufficient depth, place the workpiece on a piece of cast iron or solid steel. This minimizes the deflection from your working surface, ensuring that the maximum amount of force is transferred to the workpiece.
Working with Automatic Center Punch
Automatic center punches are slightly easier to use than the manual variety.
- Position the center punch. Placing the tip at the correct location follows the same procedure for both manual and spring-loaded center punches.
- Keep the punch perpendicular to the work surface. Once the tip is in place, ensure that the shaft is perpendicular to the workpiece.
- Press down firmly on the shaft with your palm until you hear a click. The spring inside the center punch fires the pin into the workpiece, creating an indentation.
You can adjust how hard the pin strikes the workpiece by turning the screw on the head of the punch (the orange color portion in the picture). Screwing it out decreases the impact while screwing it in increases the impact.
Tips for Working with Center Punches
Center punches work equally well on wood and metal. If you’re working with wood and don’t have a center punch, you could use a large nail instead. This could work for thin sheet metal, too, depending on the metal’s hardness.
Dan Miller is a professional toolmaker with extensive experience in the metalworking and tooling industry.
An avid DIY enthusiast and passionate hobbyist woodworker, Dan shares his expert knowledge here.