When working with an HDI board or even a conventional PCB (Printed Circuit Board), they are holes that need to be screwed shut. These holes include an open hole, a countersunk hole, a blind hole, and a counterbore hole. Often, we tend to confuse a countersink for a counterbore and vice versa. It is why we need to understand the working principles of each of them entirely.

The countersink and counterbore are holes which both require different types of specific fixtures. They are so different that it is hazardous to use one in place of the other due to ignorance. Therefore, to understand the difference between the two holes, the similarities and purposes are significant, then let us learn how to effectively fix the PCB without having to worry about falling off or loosening the accessories.

Countersink VS Counterbore

 

1、Countersink VS Counterbore

Before we start looking at the comparison between them, let’s highlight what a countersink and a counterbore are.

What is a Countersink?
A countersink is a cone-shaped hole that is bored into a PCB. This hole creates room for a flat head screw or fastener to fit correctly once installed.

What is a Counterbore?
A counterbore is more of a cylindrical flat shaped hole. The hole formed has a flat bottom and allows a screw or fastener with a flat underside to fit. Also, the instrument that is used to create this feature is also known as a counterbore. The word will be used interchangeably.

Countersink VS Counterbore

Image 1:Countersink VS Counterbore

Similarities and Differences Between Them
The practice of making a countersunk hole is known as countersinking. Now, a countersunk hole may come in different sizes of angles. It includes the standard sizes of 60, 82 and 90 degrees alongside the less popular 100, 110 and 120 degrees. However, the most frequently used degrees are 82, 90 and 100.

While the only angle applicable to a counterbore is a vertical zero degrees, it is just as effective as a countersink. It is important to note that when working with a wooden surface if you fail to countersink first but end up forcing the screw into this surface, not only will the wood’s stability and strength be compromised but your work will consequently be an eyesore.

It is because the wood fibers will crack and become dented if not wholly damaged. It is much easier to counterbore a wooden surface; this is because counterboring does not require precision and accuracy in the angles. Also, in a counterbore, all the hole needs is a screw with a flat underside or one with a socket head can fit with the surface or washer.

Counterbore are typically used for a single purpose while countersinks, due to their different angles, have different purposes. A counterbore is often similar to an enlargement of a small coaxial hole while a countersink is a conical version of that.

Use it when you don’t want the head of the fixture, or screw the bolt forward from the HDI surface you are working on. On the other hand, countersunk holes have different styles because of their different angles. With countersinking, all your screws can have the same depth.

 

2、 Countersink VS Counterbore Symbol

In drawing or design, symbols are used as a representation of the actual material or technique. With symbols, there is room for dimensional consistency and tolerance of specifications. Also, is much faster and also easier to write the symbol of material or quantity as opposed to spelling it out with actual words on a drawing. It is not only against drawing protocol but will also make your work clustered.

Symbols represent basic protocol in drawing, design or mathematics. In a building or house plan drawing, symbols are used as a faster means of conveying information. Here, the symbol of a countersink and that of a counterbore is duly represented. It is often side by side with the symbol of a diameter and accompanied by a numerical value.

What does a countersink symbol look like?
A countersink symbol looks like the letter V. When you think about it when you look at a countersunk hole from the side it resembles the letter V.

What does a counterbore symbol look like?
The symbol of a counterbore has been likened to an incomplete square with an opening at the top. In technical drawing, this symbol was formed by taking the side view of the countersink and counterbore holes.

Both symbols are used in drilling designs. With the symbol of diameter, they are used to show how wide or how deep a hole is meant to be. These designs are interpreted by a builder who works based on the information provided on these designs. A counterbore symbol is used to define counterboring operations while that of a countersink is for countersinking fastening operations.

 

3、Countersink VS Counterbore Drill Bits

You could create several holes when using a drill bit, depending on the diameter that is required and the thickness of the material. But for a counterbore and a countersink, They are hole drills, so the process created by them.

The drill bits are the instruments used for drilling or creating either a countersink hole or a counterbore into the surface of a material, which in this case is a print circuit board, PCB. Both types of holes use different materials for their fabrication. Ultimately, the aim is to create a hole where a screw or fastener can sit flush within the washer or workpiece.

It is done to completely hide the entire length and axis of the fastener or screw in the countersunk hole or counterbore. Because of the difference in their cavity, (one is flat, and the other is angled), different materials are used for their fabrication.

For counterboring, a cylindrical hole is bored into the material’s surface. This hole has a large diameter at the head and a smaller one down below. It is because the screw or fastener is meant to sit correctly in the hole and prevent the two surfaces from separating when joined. The larger side of the hole fits the head of the fastener while the smaller one accommodates its shaft.

However, countersink drill bits come in different styles and sizes to accommodate the different angles and also for different types of projects. There are about four different types of countersink drill bits in the picture above. These are the fluted bits, the cross-hole countersink, the rocker pro, and the flip style countersink.

Countersink VS Counterbore

Image 2: Countersink VS Counterbore

What to Do When Using a Countersink Drill Bit
When using a countersink drill bit, it is essential to match the size of the drill to that of the screw correctly. It is because, a countersunk hole that is too large will swallow the head of the screw or fastener while a hole that is too small will not fit the head of the screw, hence leading to a loosely fitted mount.

What happens if you forcefully drive the screw into the hole?

Nevertheless, in the case in which you forcefully drive the fastener into the hole, the surrounding materials will be damaged. It goes for both HDI and wood surfaces. Hence if your hole is shallow, the screw will not flush with the surface, and if it’s too thick, the screw will remain shallow inside it. Hence, it is essential to take measurements to make drill holes that fit the screws.

To get the appropriate measurement, adjust your countersink settings. It is the countersink size, depth of the drill bit and the stop location for the depth. Even with these adjustments, it is advisable to practice on a piece of scrap material before drilling onto the real surface, to be sure that you have the right measurements.

Lastly, to prevent chatter, do not drill too fast as this will cause uneven patterns in your material surface and your fastener will not fit into it, causing you to either abandon the material or start all over again.

 

4、When to Use Countersink and Counterbore in PCB

Now we’ve established the basics of a counterbore and a countersink hole, let’s see when it can be used in a PCB. Although both fixtures are usually for firmer surfaces like wood and metals, it can still be used on a printed circuit board.

A PCB like most circuit boards has holes and the method of drilling each hole matters. Some of these holes are screw holes, and it is used as an opening to attach the PCB onto an application. The difference in the type of screws that are available determines the type of holes you’re going to drill onto the PCB, either a countersunk hole or a counterbore hole.

Countersink VS Counterbore

Image 3: Countersink VS Counterbore

Limited Space and Mounting Security
If you’re running out of space in your device but want additional features on it, as a means to increase the flexibility of your device, you can drill a conical countersink hole into the PCB. This hole is designed to fit a typical screw with a flat head, and it requires more precision than a counterbore hole. Once the screws are flush with the board, it becomes easier to fit the PCB into the required device, either a smartphone or a watch.

However, a counterbore, although easy to fabricate, is not usually the best choice for a PCB. It is where the countersink comes in. A countersunk hole keeps the surface of the board smoother, and when done correctly, there is no interference with the arrangement of the board’s design.

However, if you require a more secure mounting of your PCB other than conserving space or going for a smoother design, then go for counterbore holes. It is because these holes are usually large enough to accommodate socket fixtures and hence the screws from it will create a more secure attachment. On the other hand, if you want to conserve space, then go for a countersink hole.

 

5、Countersink VS Counterbore PCB Applications

Usually, a printed circuit board is mounted via a screw in a hole. If you need a more evident fixture appearance and a safer installation, then either a countersink or a counterbore hole can be used.

This drilling process is often done by hand through automated equipment. Drill a counterbore when using a grub screw; the hole creates a perfect foundation for the screw to overlap and fit perfectly into the hole.

What are They Used for?
A countersunk hole in a PCB creates room for a clean installation and is ideal for tight-fitting applications in small devices. PCB countersink applications found in mobile phones and other small wearable device.

A counterbore offers a cylindrical fit to the screw. It is flat bottomed and is cut to allow a socket cap screw to be used. This hexagon socket screw has a hex head and needs to be mounted safely on the PCB. It can be found in washers and other electronic devices that require tight and secure fittings.

Countersink VS Counterbore

Image 4: Countersink VS Counterbore

 

6、Countersink VS Counterbore Dimensioning Techniques

In drawing, dimensioning is mandatory. It is the only way a builder or technician can apply the drawing in real life. Dimensioning reveals the size, type and texture of materials to be used either during construction or fabrication.

In this context, dimensioning technology refers to the method of expressing countersunk and counterbore in a design or chart, they are specified on a diagram through their dimension symbols and abbreviations. They are used to indicate the form of the surface type and offer no restrictions to its method of fabrication. These dimensions are usually represented as a note and preceded by the size through the holes.

How To dimension a countersink and a counterbore
For a countersink, the angular sides are recessed to compensate the head of the flat head fixtures which could be screws, rivets, bolts or other similar items. When drawing, Given surface diameter and an angle, and for a counter drilled hole, the diameter, depth, and included angle is also given.

For a counterbore, the flat-bottomed and cylindrical part permits the head of the fastener to lie in the recessed part. When drawing and dimensioning this, the diameter, depth and corner radius are given and specified. In a few situations, the thickness of the remaining shaft can be dimensioned in place of the depth.

Dimensioning both holes could be done in a rectangular coordinate form, Polar coordinate form.

Countersink VS Counterbore

Image 5: Countersink VS Counterbore

 

7、Conclusion

Both counterbore and countersink holes are used with their corresponding screws as an attachment to different types of materials. Using this as fixtures for a print circuit board is although not common, but it works just the same. We’ve seen that a countersink is a cone-shaped hole while a counterbore is more of a cylindrical one. In this piece, we have highlighted the differences between the counterbore and a countersink, their corresponding similarities, their definition, as well as the working principle of both holes.

Also, the name of the type of screws that fit into a counterbore and a countersunk hole is equally known as counterbores and countersinks, as the name can be used interchangeably. We have also seen the difference in their method of fabrication using the different drill bits for each type of hole. Also, for this paper, we also highlighted when we could use a countersink and a counterbore in a print circuit board (PCB) as well as their related applications and uses. Lastly, to ensure that one can see both holes and recognize them on paper, we have highlighted their different symbols as well as the dimensioning techniques that are used for each hole type.

However, for more information concerning the counterbore, countersink hole, fixtures, the PCB and HDI boards, you can reach out to us. Alternatively, if you are having problems with your current counterbore or countersinking materials like drill bits, screws or bolts and you would like to change them, all you’ll need to do is to head over to our website and place an order for what you require, and we’ll get it to you.