A Machinist’s Toolbox Staple: Punch Tools
Even though they are not necessarily the most exciting tool, punch tools are definitely a staple in the machinist toolbox. This little tool covers multiple functions in the machine shop, ranging from making reference marks, punching holes in sheet metal, beginning the predrilling process, or removing damaged rivets, bolts, or pins. And for this reason, punch tools should always be kept on hand.
Depending on your needs, there are different types of punch tools. The diagram below showcases some of them. When trying to fully differentiate them from each other, it can be a bit confusing. Due to their similarities in application use, they are used interchangeably.
Typically classified by the shape of their points, here is a bit more information about how those different points affect their performance. This will help you achieve the desired outcome.
Center punches and auto center punches are the most frequently used in machine shops. They are great for making large indentations in metal. This is necessary during pre-drilling operations and would assist in engaging a twist drill. Why can’t you just start with the drill, you might wonder? Bypassing the punch step often leads to the drill veering off center and damaging the workpiece.
The only difference between these two types of center punches is that the auto center punch does not require a hammer. There is a mechanism that automatically forces the punch into the metal.
Check out this diagram to see of how the automatic center punch works.
Prick punches are ideal for creating reference marks on your workpiece. Why do you need reference marks? This is very helpful when transferring dimensional information from paper to the metal. Just place the paper directly on the metal and punch! Prick punches are similar to center punches and are also used as a predrilling tool. However, a prick punch can create a deeper hole than a center punch. The indentation is then enlarged with a center punch.
Drive punches are often used with materials other than metal, however they are extremely handy if you need to remove any damaged rivets, bolts or pins that are wedged in holes. The drive punch is not featured in the diagram, but the anatomy is similar to those listed. The only difference is that it has a flat face rather than a point.
Drift pins are typically used directly after the drive punch. When the drive punch has unwedged an object (like a damaged bolt) sufficiently, the drift pin is then used to finish the job and pluck out the object from the hole.
Starting punches and pin punches are often times used together as the starter punch loosens a stuck pin and the pin punch is used to finish the job. You will see that this is similar to the drive punch and draft pin system.
Aligning punches are similar to the drift pins in that they work with pins, rivets, and bolts. However, the aligning punch is ironically not designed to be hammered and its purpose is to align two or more holes so that an insertion can be placed properly for accurate fastening.
Transfer punches (not noted in the image above) are punches that are not tapered. The transfer punch is designed to be able to fit into an existing hole and then accurately transfer the size of that hole to another surface.
Although the practice of punching appears simple, it is important not to hit the punches too hard. If punched too hard, you can damage the tool itself and bend it out of shape, create dimples the metal around the punch, or actually punch all the way through the metal.
Ensure that you have the correct tool to punch it, we recommend a ball peen hammer like this one.
Another tip when using one of these punch tools is to begin by tilting the tool away from you and walking it towards the point. This is instead of just directly placing the tool on the desired point. This allows you to see that the punch tool is aligned with the desired punch location. Then, you can tilt it back upright and punch it.
Punch Tool Models
This is an automatic center punch. The moveable components are made from hardened tool steel and the point can easily be removed for sharpening. With this tool you have control over the type of impact you wish to make, as the screw cap all the way down makes heavy indentations and the cap upward to be lighter markings.
The points are hardened steel for wear resistance and the shank is tempered steel for optimal strength. The shank has a square like design so that it does not roll away when you place it down. This set comes with 7 center punches are even a round case for storage.
Interested in the Starrett models above but don’t need that many? Here is an individual option. The shank is knurled for better grip and the steep is hardened and tempered.
This prick punch is 4.5 inches in overall length and has a black oxide coating which will protect the tool against corrosion. The pointed and hardened tip is great for thin metals.
This set of transfer punches comes with an easy to see and use stand that keeps the tools stacked and ready to pull. The sized of the transfer punch in this set vary from 3/32″ to 1/2″ by 1/64 inch increments and includes the highly used 17/32″. Each punch is made from high-quality heat-treated alloy steel and feature a black oxide finish for rust resistance.
The entire tool is heat treated to create a hardened tip that will allow the tip to remain precise in its size and shape. This punch is made from premium high carbon steel.
This drift pin is made out of tough forged steel for enhanced durability. The tool is rust resistant and heat treated for optimal strength and thus is built to last.
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