In a recent conversation with a customer one of our technical engineers was asked which would be best suited to a specific application; a ball screw or a lead screw.
We recognised that this is a question we’ve been asked a number of times in the past – and will no doubt be asked again in future – so we thought it would be helpful if we explored some of the pros and cons of ball screws vs lead screws, with some examples of where each are well suited.
This may help you to decide between the available options for your own application, and narrow your search for a spindle which best meets your needs.
You’ll see from our product pages that we offer a range of screw jacks, linear actuators and the spindle ranges from Grob and ADE– which cover a huge range of potential linear motion control on a wide scale, and for a wealth of different environments.
This means that you have a lot of options for making the best choice for your application – but it also means that, if you’re unsure which direction to focus your search, the range of options can be a little overwhelming.
One way to help understand some features and differences; lead and pitch are a good example of related, but different, specifications. Lead refers to the linear distance travelled for each complete turn of the screw, while pitch is the distance between screw threads. These terms are often used interchangeably, and for single-start screws (see below for definition), lead and pitch are equivalent.
However, lead and pitch are not equal for screws with multiple starts;
Let’s explore the difference between a lead screw and a ball screw:
What is a ball screw?
You’re probably familiar with ball bearings – and the smooth motion that they provide in rotation; a ball screw utilises these ball bearings within the screw mechanism, recirculating balls within circuits, meaning that the screw shaft which passes through the ball nut rotates smoothly using ball point contact – which offers very low friction and close contact between ball and screw.
This gives you great control over the linear motion, with high efficiency and positional accuracy. Low friction means that you need less rotary input power to create the linear motion – allowing for a smaller powered motor; this not only means that cheaper options for motors are suited, it also allows for a smaller footprint.
A key benefit in the ballscrew design is lead options: very fast lead can offer very fast linear motion for high speed positioning, with low friction for high duty usage. Close ball contact offers low backlash when changing direction, and can be preloaded with zero play using larger ball sizes. Precision and error can be controlled with different precision grades of manufacture from rolled to ground forms.
So in summary: ball screws are better suited to applications where speed, positional accuracy and high usage/duty is required; however, you will also need to factor a braking system into the design, as ball screws are not self-locking.
What is a lead screw?
A leadscrew (trapezoidal or acme thread ) differs from a ball screw; there are no ball bearings – meaning that the screw threads are in direct contact with the moving component – i.e. the bronze nut acts as a plain bearing, with much higher surface area of contact.
Higher forces are possible, but this contact creates more friction – and thus requires more power from the motor. The cut or whirled threads offer a more shock-resistant, self-locking system (depending and thread angle) meaning that you need no additional braking system for them to maintain their position.
Single and multi-start options are available for some faster leads but not as fast as a ballscrew. These are well suited to low cost, low speed and lower duty environments where occasional, significant linear motion is necessary.
What are the pros and cons of ball screws?
- Higher positional accuracy
- High speeds and lead options
- Require less torque so smaller, cheaper motors
- Energy efficient
- Low friction
- Run at low temperatures for high duty
- Adjustable for preload and axial play
- Require braking systems
- Require grease or oil lubrication
- No self-locking
- Less shock-resistance than lead screws
- More expensive
What are the pros and cons of lead screws?
- Lower cost than ball screws
- Self-locking (dependant on thread angle)
- Do not always require braking system
- Can be self-lubricating bronze or plastic nuts
- Can carry heavier loads than ballscrew screw counterparts
- Require more regular maintenance, costing more long-term
- Less efficient; require greater torque/larger motor
- Higher friction, thus run at a higher temperature
- Not as well suited to high-speed applications or continuous/long cycle times
- More axial play/lower position accuracy
So which should I choose – a ball screw or a lead screw?
Hopefully the information here has given you a better steer on which option would be best suited to your application. If you’re still unsure whether a ball screw or a lead screw spindle would best suit your design, speak to the Drive Lines team today for advice on the range, and which would meet your specific needs.