How to Enlarge a Hole in Metal?

This is the point to remember: to enlarge a hole in metal you must not simply use a larger drill bit. Especially when working with metal, the risk is to damage both the equipment and the object of your attention.

Actually we are talking about precision operations in which you must not improvise: you need specific equipment and particular techniques to enlarge and countersink a hole made previously. Do you want to deepen your knowledge and carefully choose the techniques to use?

Why do you need to enlarge a hole in metal?

There is a screw that doesn't fit, in other cases you need to accommodate an element of different shape. The needs can be different. In some cases it is necessary to correct a hole in a plate to let a wider bolt pass, in others instead a countersink is needed.

This is a precision operation to insert, for example, a conical screw. Or a larger diameter hole is needed to draw a real circle in the metal. The reasons that should lead you to enlarge a hole made previously in steel or iron are different but what is needed is always the precision of the hole execution.

What are the methods you should not follow?

Often people tend to enlarge and countersink holes in metal with wrong methods. For example, one of the worst solutions is to use the drill bit as a kind of mill, rotating around the circle to enlarge the hole made previously.

Bad idea, you damage the bit and do an imprecise job. You might think of increasing the circumference of the hole with a larger iron drill bit but there are specific bits you can use. And exploit for metal working.

The difference between boring and countersinking

Before proceeding with listing tools and techniques for correcting a hole in iron or steel you must remember a point: on one hand there is countersinking, on the other hand boring to enlarge the hole. In the latter case we are talking about a precision operation to correct a pre-existing hole in terms of diameter. Can the operation be carried out with larger bits?

Yes but there are precision tools that are used to avoid burrs and approximate results. Countersinking, on the other hand, is an operation to remove material to enlarge the hole with a particular shape suitable for accommodating certain shapes. For example, countersinking is the one done on a hole already made to accommodate countersunk screws.

The bits for enlarging a hole in metal

There are different tools to be used in specific conditions. To bore a hole in metal, whether it's iron or stainless steel, you must not rely on a single tool. For quality work we need specific bits. For example?

Cup mills

Different solutions for different purposes. Our catalog offers you all the necessary options to enlarge a hole in metal. Let's start with a clear need: how to bore a hole by going from a reduced diameter to a particularly large one?

You can use the bimetallic cup mill in HSS, that is high speed steel. This solution allows you to shape particularly large circular forms on metal planes, plates and sheets. Here above you can see a video tutorial of the tool.

Bits for enlarging holes

These conical-shaped tools that are mounted on hand drills and column drills are designed specifically to enlarge holes in sheets and tubes. The stepped shape allows enlargement with millimeter precision so you get the size you need.

You find solutions in high-speed steel (HSS) and Tin, that is coated with titanium nitride to increase durability over time. Then there are those in TiAIN which are perfect for intensive use. The helical cutting edges guarantee performance and cutting precision.

Bits for countersinking

If you want to perform a good countersink and enlarge a hole following a particular angle you can use the Krino countersink and counterbore bits with 3 cutting edges. These solutions are both in HSS and with the addition of Tin (the difference in the image below).

That is with titanium nitride coating that serves to reduce friction and increase both duration and performance on metal. All countersinks have the useful fitting to be used on ordinary drills and you can choose the model based on the angle needed. However there are also countersinks for flat-head screws and hand tools to operate in specific conditions.

The choice of these tools is fundamental for countersinking holes but always remember that a good solution, in these cases, is to use a column drill to have greater precision. Also and especially in the work repetition phase. An essential choice is the Krino countersink with 3 cutting edges at 90° with asymmetric HSS and HSSCO geometry that works well on alloy steels, cast irons and, in the 5% cobalt version, also on stainless steel.