What Changes When You Go From 5mm to 10mm?
Ball screw lead is simply the linear distance traveled by the nut during one revolution of the screw.
With a 5mm lead, one revolution moves the nut 5mm.
With a 10mm lead, one revolution moves it 10mm.
That gives us a very simple speed calculation:
Linear speed = Screw RPM × Lead
For example, at 2,000 RPM:
- 5mm lead → 10,000 mm/min
- 10mm lead → 20,000 mm/min
So if your motor can only run at a certain RPM, increasing the lead is an easy way to get more linear speed.
The problem is that you don't get that speed for free.
The Trade-Off Is Speed vs. Mechanical Advantage
A larger lead reduces the mechanical advantage of the screw.
A simplified thrust relationship is:
F ≈ 2πTη / L
where:
- F = axial thrust
- T = motor torque
- η = ball screw efficiency
- L = lead
If everything else stays approximately the same, doubling the lead from 5mm to 10mm roughly halves the available thrust for the same motor torque.
That's the part I would pay attention to when comparing two screws.
A 10mm lead can make an axis faster, but the motor has to work harder to produce the same thrust.
A 5mm lead gives you more mechanical advantage, but you need more screw RPM to achieve the same linear speed.
Neither one is automatically better.
Start With the Speed You Actually Need
Let's say an X-axis needs to reach 15,000 mm/min.
With a 5mm lead:
15,000 ÷ 5 = 3,000 RPM
With a 10mm lead:
15,000 ÷ 10 = 1,500 RPM
If the servo motor is rated for 3,000 RPM, the 5mm screw is already operating at the motor's nominal speed just to reach the target rapid speed.
The 10mm screw gets there at half the RPM.
That can be a big advantage, especially on a long axis where screw speed is already becoming a concern.
But don't stop the calculation there.
You still need to check torque and thrust.
Now Check the Load
Imagine the same motor is driving either a 5mm or 10mm lead screw.
The 5mm version has twice the mechanical advantage of the 10mm version, assuming the other parameters are comparable.
So if the machine has a heavy moving load or significant cutting resistance, the 5mm lead may be the better choice.
This is particularly relevant for:
- Vertical Z axes
- Heavy CNC tables
- Clamping mechanisms
- Lifting systems
- High-load positioning axes
- Applications requiring relatively high thrust at low speed
For these machines, maximum rapid speed may not be the main problem.
Having enough torque to move and accelerate the load may be.
Why 10mm Lead Is Attractive for Fast Axes
Now take the opposite situation.
Suppose you have a horizontal axis with a relatively light load. The machine needs fast rapid movement, but the servo has a limited maximum RPM.
A 10mm lead can make the design much easier.
For example:
| Required Speed | 5mm Lead | 10mm Lead |
|---|---|---|
| 5 m/min | 1,000 RPM | 500 RPM |
| 10 m/min | 2,000 RPM | 1,000 RPM |
| 15 m/min | 3,000 RPM | 1,500 RPM |
| 20 m/min | 4,000 RPM | 2,000 RPM |
| 30 m/min | 6,000 RPM | 3,000 RPM |
This is one reason larger-lead ball screws are commonly considered for high-speed linear motion.
You don't have to spin the screw as fast to get the same axis speed.
And that matters more as the screw gets longer.
Long Ball Screws Change the Decision
A 300mm screw and a 1,500mm screw shouldn't be treated the same way.
As screw length increases, critical speed becomes more important. A long screw rotating too quickly can develop whip and vibration. Support configuration, screw diameter, end machining, and mounting all affect the actual operating limit.
This creates an interesting situation.
You may start with a 5mm lead because you want more thrust. Then you calculate the required RPM and discover that the screw would have to run much faster than you'd like.
At that point, moving to a 10mm lead may be the better engineering decision.
For a long-travel axis, I would rather run a suitable 10mm lead at a reasonable RPM than force a 5mm screw to spin unnecessarily fast.
What About Positioning Resolution?
This is where the discussion often gets mixed up with ball screw accuracy.
A 5mm lead gives half the linear movement per revolution compared with a 10mm lead.
That means the motor has finer mechanical displacement per revolution.
But that does not mean a 5mm screw is automatically twice as accurate.
For example, a C7 5mm ball screw is not automatically more accurate than a C5 10mm ball screw.
Lead size and accuracy grade are different specifications.
Actual positioning performance can also be affected by:
- Ball screw lead accuracy
- Ball nut preload
- Axial bearing clearance
- Linear guide accuracy
- Coupling stiffness
- Machine frame rigidity
- Servo tuning
- Encoder resolution
- Thermal expansion
So if someone says, “I need 5mm because I need better accuracy,” I'd ask for the actual positioning requirement.
If the requirement is ±0.02mm, that's a useful engineering number.
“I want a more accurate screw” isn't.
5mm Lead Is Often Useful on a Z Axis
The Z axis is a good example of where a smaller lead can make sense.
The motor has to deal with the weight of the spindle and tooling, and depending on the machine design, the axis may need relatively high thrust at moderate speed.
A 5mm lead provides more mechanical advantage.
For example, a CNC machine might use:
- 5mm lead on Z
- 10mm lead on X
- 10mm lead on Y
That can be a perfectly reasonable configuration.
But it isn't a rule.
If the Z axis is lightweight and needs very fast movement, 10mm could make more sense. If the X/Y axes carry a heavy gantry, 5mm might be preferable there too.
The axis requirements decide the lead—not the other way around.
Don't Forget Acceleration
Maximum speed gets most of the attention, but acceleration can be just as important.
A machine that moves 20,000 mm/min doesn't necessarily need the same motor torque as a machine that takes several seconds to reach that speed.
During acceleration, the motor has to overcome the inertia of:
- The moving load
- The screw
- The coupling
- The motor rotor
- Other rotating components
A heavy gantry that has to accelerate quickly can require considerably more torque than the same gantry moving slowly.
That's why I wouldn't size a ball screw from maximum speed alone.
If the machine has aggressive acceleration and deceleration, calculate the torque requirement for that part of the motion profile too.
What Happens If You Choose the Wrong Lead?
The problems are usually pretty obvious once the machine is running.
Lead too small
A 5mm screw may give you plenty of thrust, but the required RPM can become excessive.
You may run into:
- High screw RPM
- Vibration
- Heating
- Critical-speed limitations
- Reduced maximum travel speed
- Higher motor speed requirements
Lead too large
A 10mm screw can solve the speed problem but introduce a different one.
You may have:
- Lower available thrust
- Higher motor torque requirements
- Less mechanical advantage
- Difficulty accelerating heavy loads
- Insufficient force on a vertical axis
So don't ask only:
“Which lead is faster?”
Ask:
“Which lead gives me the speed and thrust I need without pushing the motor or screw outside a sensible operating range?”
That's a much better question.
A Quick Example
Let's say you are designing a 600mm horizontal CNC axis.
The requirements are:
- Moving load: 30kg
- Maximum speed: 15m/min
- Servo speed: 3,000 RPM
- Moderate cutting force
- Horizontal installation
With a 5mm lead, the screw needs 3,000 RPM to reach 15m/min.
With a 10mm lead, it needs only 1,500 RPM.
If the required thrust is relatively low, the 10mm lead starts to look attractive.
But if the same axis carries a much heavier load or requires substantially higher cutting force, the 5mm lead may provide a useful torque advantage.
That's why the same screw diameter can be offered with several different leads.
The manufacturer isn't necessarily making one version “better.”
They're giving the machine designer different options.
What About a Linear Scale?
A linear scale changes part of the positioning equation.
With rotary feedback alone, the controller knows how much the motor has turned. With a linear scale, the control system can measure the actual position of the moving axis.
That can help compensate for some transmission errors, including ball screw lead error.
But it doesn't make the mechanical system irrelevant.
A linear scale won't fix:
- Mechanical backlash
- Loose bearing supports
- Coupling movement
- Poor guide alignment
- Structural deflection
- Excessive friction
- Thermal problems
So even on a closed-loop linear feedback system, the ball screw still needs to be properly sized.
The difference is that lead accuracy may become less dominant in the overall positioning error budget.
So Which Lead Should You Use?
As a starting point, I'd look at it this way.
Consider a 5mm lead when:
- The axis needs relatively high thrust
- The load is heavy
- The axis is vertical
- Low-speed control is important
- Motor torque is limited
- Maximum speed is moderate
Consider a 10mm lead when:
- High linear speed is important
- The axis has long travel
- Motor RPM is limited
- The moving load is relatively light
- Cycle time is important
- The available motor torque is sufficient
For many general CNC applications, either can work. The important thing is making sure the motor, screw, bearings, and machine structure are designed around the same operating point.
A Better Way to Ask Your Ball Screw Supplier
Instead of sending:
“I need a 16mm 5mm lead ball screw. Please quote.”
Give the supplier enough information to check the application.
For example:
Axis: X-axis
Travel: 600mm
Moving load: 30kg
Maximum speed: 15m/min
Acceleration: 0.5G
Installation: Horizontal
Motor: 750W servo, 3,000 RPM
Required positioning accuracy: ±0.02mm
Duty cycle: 8 hours/day
With that information, the supplier can compare 5mm and 10mm leads based on the actual application.
That is much more useful than starting with the screw specification and trying to make the machine fit around it.
5mm or 10mm? Look at the Whole Axis
If I had to reduce the decision to a simple engineering check, I'd use this order:
1. Determine the required linear speed.
Calculate the screw RPM for both leads.
2. Determine the required thrust.
Check whether the motor can produce enough torque through each lead.
3. Check the screw speed.
Especially for long screws, make sure the required RPM is within a sensible operating range.
4. Check acceleration.
Don't forget the torque needed to accelerate the actual moving mass.
5. Look at the application.
A vertical load, heavy CNC gantry, high-speed transfer axis, and light-duty automation axis may need completely different lead choices.
6. Then look at accuracy and resolution.
Don't use lead size as a substitute for specifying the actual positioning requirement.
Final Thoughts
A 5mm ball screw lead is not simply the “precision” option, and a 10mm lead is not simply the “high-speed” option.
The lead changes the relationship between motor torque, screw RPM, thrust, and linear speed.
If the axis needs more thrust and doesn't require extreme speed, 5mm can be a very practical choice.
If the axis needs high-speed movement and the motor or screw cannot run at very high RPM, 10mm may be the better option.
The mistake is choosing the lead before doing the basic calculations.
For a new machine, I would start with four numbers:
load → required thrust → required speed → available motor RPM
Those four numbers will usually tell you whether 5mm or 10mm is worth looking at.
Then check screw length, critical speed, acceleration, accuracy, and installation conditions.
The best ball screw is not the one with the largest lead or the highest specification.
It's the one that gives the machine the right combination of speed, thrust, and control without making the rest of the system work harder than it needs to.
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