BLOG » The Essential Guide to Counterbore Holes’ Features

The Essential Guide to Counterbore Holes’ Features

After seeing in our latest blog on the different types of holes, we are continuing our guide on design and manufacturing by diving deep into the specifics of counterbore holes. In this blog post we are going to see what differentiates a counterbore hole from countersink holes, its processing methods and some of the most common issues that might occur during manufacturing.

Counterbore vs countersink: what are their features

Counterbore and countersink holes have similar features, but they come with substantial differences.

Counterbore holes

A counterbore hole has a cylindrical shape and it is a specialized feature that enhances assembly processes by creating a recessed area with a larger diameter at the top. It allows for flush and seamless connections with screws, bolts, or dowels. This ensures precise alignment, improved stability, and a polished finish for various engineering applications. It is an essential feature when using screws that need to be concealed or embedded in thin plates or materials such as plastics.

Countersink

Countersink refers to a hole with a chamfered edge in a conical shape. Some screws and bolts have conical-shaped heads, known as countersink heads. To accommodate these countersink screws and bolts, the corresponding holes need to be machined in a similar conical shape. This ensures that the screws fit snugly into the holes and do not protrude from the surface of the material. You can find countersink holes on your computer, for example. The outer covers are, in fact, secured with screws that are flush with the surface, thanks to the presence of countersink holes.

When uploading your part on meviy, model the angle of the conical shape to be 90°. Our AI, in fact, might not recognize other angles and you might not receive your automatic quotation.

Counterbore holes’ processing methods

There are several methods for processing counterbore holes, and the choice of method depends on the material being worked. Each method has its own cost and dimensional accuracy considerations. Below, we introduce the main processing methods and their characteristics.

Machining

Machining involves chamfering the hole using a drill specifically designed for these holes, attached to a drill press. It is important to use this specific drill, as using other drills may result in an improper shape that does not properly accommodate the screws. Machining is commonly used for metal shafts, cutting of plastic materials, stainless steel and aluminum blocks. It is also used in sheet metal fabrication and pressing, although it can increase processing costs. This process is used for both counterbore and countersink holes.

Friction drilling

Friction Drilling is a process used exclusively for counterbore holes. By drilling, the outer perimeter of a counterbore hole in a thin sheet is raised into a cylindrical shape. It is commonly used in sheet metal fabrication and pressing. Friction drilling can be used as an alternative to embossing for positioning, or to achieve effective screw depth in thin sheets. It is possible to create a counterbore hole shape using the drilling process.” By using specialized molds, the desired shape can be formed. Additionally, by tapping the hole, it can be used as a hole for countersunk screws.

Considerations and Issues in Counterbore Hole Processing and Design

Counterbore holes are essential when using countersink screws, but there are important considerations in processing and design. Below is one of the most common one:

Countersink screw protrusion

If countersink screws become loose, they may protrude from the surface of the plate. Countersink screws are secured by the contact between the conical section and the hole. However, if the axis of the tap and the axis of the counterbore hole for inserting the screw are misaligned, the conical section will not make surface contact but rather point or line contact. Therefore, strict tolerances must be specified to ensure proper alignment of the tap hole and the counterbore hole.

Another solution to prevent loosening is the use of adhesives. The adhesive “Loctite” is well-known for this purpose. It is applied before tightening the screw and solidifies upon tightening.

Conclusion

In this article, we introduced the processing methods and design considerations for counterbore holes. When working with counterbore holes, it is important to verify the dimensions based on JIS standards and the specifications of the countersunk screws to ensure that they do not protrude. Additionally, pay attention to the positional accuracy to prevent the countersunk screws from loosening and protruding.

At meviy, we offer various hole processing services, including straight holes and counterbore holes, for sheet metal components and machining plates.