What Is Cam Out & How To Stop It

Unlocking the Mechanics of Cam-Out

In the realm of precision engineering, understanding the phenomena of 'Cam-Out' can be a game-changer. This article unpacks the mechanics of Cam-Out, identifies its root causes, and offers actionable strategies to mitigate its occurrence. So, whether you're a seasoned engineer or an apprentice, there is no doubt that mastering the art of preventing Cam-Out can elevate your skillset, and this article provides a blend of conventional wisdom along with innovative solutions to tackle this age-old engineering challenge.

What Does “Cammed Out” Mean?

Cam-Out or ‘screw cam out’ is a term you may have heard but don't truly understand its meaning.

Camming out is when a screwdriver or drive bit twists inside the head of the screw, creating an outwards force on the driver. In turn, reducing the engagement of the tool and decreasing the amount of torque transferred from the driver to the screw itself.

This is often one of the early stages of a screw head beginning to strip, and will cause “skipping” or grinding of the drive bit, wearing away the drive recess. 

Eventually, there becomes a point where the screw becomes so worn, that it can no longer be used. Don't worry if this happens as we have a helpful guide to show you ways to remove a stripped screw.

Over the decades, innovation has driven tool manufacturers to create new cam-out-resistant drives. Although camming out remains an engineering nuisance, it is vital to know how to prevent it and what to do when it occurs.

First, let’s see why it happens in the first place…

What Causes Cam Out?

One of the ways camming out emerges is by driving a screw at too high of a speed with not enough pressure applied. This then causes the drive bit to twist and/or slip inside the head of the screw leading to the torque being inefficiently transferred.

This high-speed grinding effect generates a lot of heat, causing damage to the bit and the screw head. Applying insufficient perpendicular force through the driver bit also increases the likelihood of this happening. 

The second way in which cam out occurs is when driving screws with more torque than what the interlocking friction between screw and screwdriver can handle. Exceeding this threshold causes the driver bit to slip and lose screw engagement leading to it eventually moving up and out of the screw head, often leaving a damaged screw head and bit.

Now that we know a little more about why it occurs, let’s look in depth at ways that we can reduce the chance of screwdrivers camming out in the first place.

How To Stop Cam-Out

A key engineering skill is learning how to stop cam out in the first place. There are many ways to avoid screw cam out, which most engineers harness with practice throughout their apprenticeship. 

We suggest always carrying out this quick checklist to ensure that you avoid cam out when driving a screw.

1. Ensure That the Drive Bit Is the Correct Size

Check that the drive bit is the correct size and type for the screw head. Using a slightly smaller bit than the screw or of the wrong type (e.g. Pozi for a Phillips) can cause slippage. Therefore having the right size bit can significantly reduce the risk of camming out. 

Pro tip: Every time you use a new batch of screws or driver, check that the tip and head mesh perfectly before attempting installation. While this may sound very simple, it can genuinely make a difference.

2. Ensure That You Are Applying the Right Amount of Pressure

Applying steady pressure through the drive bit or screwdriver helps to ensure that the tip engages fully with the screw head and cannot slip easily. It is important to efficiently transfer as much torque as possible to the driving of the screw without allowing it to cam out. Once camming out begins, even greater pressure will be required to stop it due to the decreased friction caused by the inconsistent mesh between the screw head and the drive tip.

3. Always Screw Perpendicular to the Surface of the Material

Another simple tip that can help to combat camming out is to avoid tilting the screwdriver off-centre when installing the screw.

Being perpendicular, or maintaining a 90-degree angle between the surface of the material and how you position the driver into a screw head can help ensure that the fixing installs smoothly.

If you're in a tight space, there are flexible shaft screwdrivers which can allow the handle to be held at an angle while still keeping the tip correctly aligned.

4. Maintain a Close Eye on the Screw Head

This may sound a little obvious, but it is essential to always pay close attention to the movement of the bit inside the screw. It allows you to stop driving the moment you notice the bit starting to cam out and prevent further damage. 

For example, if you feel the screwdriver begin to push back or rise up out of the screw head it’s time to stop as you’re about to cam out.

5. Use a Lower Drill Speed

Don’t let slowing down the whole process go overlooked. Using a power tool can make the assembly process faster and more convenient, however, you may also find it harder to gauge how much force you are applying. By using a lower drill speed you allow yourself more chance to notice the screw starting to cam out and prevent it from causing damage by either applying more pressure or stopping altogether.

6. Try Using a Manual Screwdriver Rather Than Power Tools

Don’t doubt the power and reliability of the mighty screwdriver! In fact, their slower speed can help to avoid camming out as it allows you to quickly adjust the applied pressure to increase the efficient transfer of torque and avoid the driver slipping which is often caused by an imbalance between pressure, torque and speed.

Ratchet screwdrivers are a very practical choice as they allow you to drive screws tightly with less effort than a typical screwdriver while still allowing all the control of their traditional counterpart.

There are also torque-limiting screwdrivers which can all but stop camming out entirely as you should in theory never go above the torque limit of the screw you’re driving.

7. Use Pozidriv Bits Rather Than Philips

While Phillips drives are well known for their overall versatility, they are also very susceptible to camming out.

The Pozidriv drive type presents a technically superior alternative to the traditional Phillips drive in cases requiring higher torque. Its design, characterised by an additional cross at 45 degrees, enhances the torque transfer efficiency, resulting in less chance of cam-out and more reliable fastening. 

Your New Toolkit for Mastering Cam-Out

Navigating the challenges of Cam-Out is essential for any engineer focused on precision and reliability. By following the simple checklist above, you can significantly reduce the chance of screwdrivers camming out. By combining tried-and-true methods with new approaches, you're now better prepared to tackle Cam-Out, making your engineering projects more efficient and dependable.

FAQs

What does it mean to cam out a screw?

Cam out occurs when a drive bit or screwdriver slips off the screw head while driving it in, resulting in potential damage. This often happens when using power tools as the torque generated can cause the drive bit to slip and pop out of the screw head before you have a chance to do anything about it.

Do impact drivers cam-out?

In short, yes, any type of driver can cam out once the torque threshold required to drive the screw has been surpassed. One thing to note is that due to the additional impact provided by impact drivers, is it far easier to damage screw heads beyond their usability so be careful.

What is the difference between Phillips and Pozidriv?

While Phillips and Pozidriv screws might seem alike, their different driver shapes result in distinct practical differences. Phillips screws have a central cross with straight slots, making them versatile but prone to camming out under pressure. In contrast, Pozidriv screws have an additional cross at 45 degrees, offering better torque transmission and reducing cam-out risk when high torque is applied.

To learn more about Pozidriv and Phillips drive types, we recommended reading the difference between pozi and phillips.

Which drive type is resistant to cam out?

For general applications and especially for countersunk screws, drive types such as Pozidriv or Torx are an excellent choice. They are specifically designed to reduce the chances of camming out by having more surface area for secure engagement between the driver and the screw head. 

Other anti-cam out screwdriver bits include square and socket head drive types, though these work better for protruding screws.

For additional reading and to find out more about what is the best screw drive for your project, read our article which explains every drive type currently available.