Ball Screws from Automotion
A ball screw is a screw which translates rotary motion into linear motion. Normally used as the driving mechanism in horizontal or vertically driven applications aided by linear guides for supports.
They are described by diameter and pitch or lead. The pitch or lead is the amount of travel you get, or distance the nuts travel along the screw for every complete revolution. They can be operated manually or motorised. They differ from lead screws in that they offer greater precision, speeds, efficiency and accuracy. They are a precision screw which cost considerably more than a lead screw of comparable size so it is important to determine if your application really requires a ball screw. Please contact us if you need any help with this.
Ball Screw Options
Rolled ball screws in sizes from 16x5mm up to 80x10mm. Typically stocked in 3000mm lengths but available up to 6000mm.
Wide range of supports including EK, EF, BK, BF, FK, FF, AK, AF and more.
Miniature rolled ball screws and nuts come in 6 -14 mm diameter sizes and with lengths up to 1 metre.
Product Videos
I: Lead screw vs. ball screw
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II: Application and setup of lead/ball screws
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III: Selection of guides to accompany lead/ball screws
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Ball Screws Product Selection
Product Selection
L1380
L1388
L1385
L1390
Standard ball screws
L1380
L1381
L1382
L1383
Miniature ball screws
L1379.F
L1379.C
Rolled ball screws
| Ø | 5 | 10 | 16 | 20 | 25 | 40 | 50 |
| 16 | • | • | • | ||||
| 20 | • | • | • | ||||
| 25 | • | • | • | ||||
| 32 | • | • | • | ||||
| 40 | • | • | • | • | |||
| 50 | • | • | • | ||||
| 63 | • | • | |||||
| 80 | • | • |
Miniature ball screws
| Ø | 1 | 2 | 3 | 4 | 5 | Nut |
| 6 | • | flanged | ||||
| 8 | • | • | • | flanged | ||
| 10 | • | • | flanged/cylinder | |||
| 12 | • | • | • | flanged/cylinder | ||
| 14 | • | flanged/cylinder |
Ball Screws General Guidance
General Guidance
When selecting a ball screw some of the main factors to consider are:
- Maximum required travel speed
- Maximum axial compression (buckling load)
- Method of support of the ball screws
- Type of unit required, fl anged, cylindrical etc.
In general it is best to support the ball screws with our ball screw support units (L1388 to L1406) with a fixed end (generally where the motor is mounted) and a floating (support) end. The support units are selected to suit the loads likely to be required, the size of the ball screw (especially its core diameter) and the type of mounting required. Details of the machining required for each end of the ball screw are shown in the bearing mounts technical section.
The data table for the ball screws show the diameter, the lead of the ball screw (i.e. how far the nut travels for one complete revolution of the screw) as well as the mass moment of inertia (also known as the rotational moment of inertia) - this is the extent to which an object resists rotational acceleration about its axis.
Maximum speeds and buckling load data are shown in the technical pages. When using a ball screw the ambient temperature should not exceed +80°C.
During assembly, the parallel alignment of the guides should be ensure. The details on the concentricity of the ball nuts to the ball screws are shown on the technical pages. For linear guideways for use with ball screws please see our part numbers L1016 etc.
Lubrication - the ball screws must be adequately lubricated. This is dependent on load, speed, motion sequence and temperature. Do not use lubricants containing Mo/So or graphite.
In general, the ball nut is already on the ball screw and should not be removed. If you need to machine the ball screw, then the plastic mounting sleeve should be used to retain the ball bearings whilst the nut is removed.
Mounting the nut on the screw
Sometimes ball screws are delivered with a separate ball nut. When mounting the nut on to the screw take care as if done incorrectly the ball bearings may come off the ball nut.
Ball nuts should be mounted only with the help of a plastic mounting sleeve (delivered with the nut). The start of the thread should be aligned so that the seal and the internal parts of the nut are not damaged.
- Remove the rubber washer from one side of the sleeve. Push on the nut with the sleeve on the end of the screw. Press the sleeve against the start of the screw thread.
- Screw the nut onto the thread using a slight axial pressure, then screw the nut on for it’s entire length.
- Remove the mounting sleeve only when the nut is completely threaded on to the screw.
- Lock the nut on to the screw (to prevent any unscrewing) using an O ring or similar - whilst installing the system.
If the balls do unfortunately escape...
- Pick them up (the nut is only compatible with the original balls). The load capacity can still be achieved if one or two balls are missing.
- Carefully clean all parts, use the sleeve as a mounting jig and replace the balls.
- Start with the lowest circuit. Insert the balls into the nut circuit - the sleeve prevents the balls from falling out again.
- Do not place the balls in the empty circuit located between the two deflectors.
If you have any technical queries please call 01483 26 67 74
Ball Screws Technical Specs
The maximum axial loads are the loads at which a ball screw will not buckle under compressive loads in the axial direction.
For ease of use the total maximum axial loads are shown in the following graphs.
Factors are:
- Type of supports
- Screw diameter (core)
- Length between supports
Apply 50% to the graph figures - to provide a margin of safety.
Ball Screws Calculations
| n1 | n2 | |
| Fixed-floating | 2 | 10 |
| Fixed-fixed | 4 | 20 |
| Fixed-free | 0,25 | 1,3 |
A ball screw of size 40ø. This has a core diameter of 35.8mm.
Distance between the support parts is 600mm.
Using a fixed and floating bearing arrangement.
Reading of graph 1 (fi xed-fl oating) the maximum axial load is going to be 50,000 N (approximately 5 tons).
Example:
Buckling load calculation - Method 1
Buckling load calculation - Method 2
Average speed and average load:
In the event of variable operating conditions (speed and load), the working life calculations will rely on the average values Fm and nm.
For the average speed nm, in the case of variable speed, apply:
nm = average speed (rpm)
q = time (%)
For the average load Fm, in the case of variable load, apply:
Fm = average load (kN)
q = movement or time at constant speed (%)
For the average load Fm, in the case of both variable load and speed, apply:
Fm = average load (kN)
q = time (%)
nm = average speed (rpm)
Nominal working life:
Working life L, expressed in revolutions:
L = working life (in rpm)
Fm = average load (kN)
Ca = dynamic load capacity (kN)
Working life L, expressed in hours Lh:
Lh = working life (h)
L = working life (in revolutions)
nm = average speed (r.p.m)
OT = operating time (%)
Output Torque (Nm)
Output torque Mt, for the transformation of rotational movement into linear movement:
Resistive torque Mr, for the transformation of linear movement into rotational movement:
Mt = output torque (Nm)
Mr = resistive torque (Nm)
F = actual load (kN)
P = pitch (mm)
η = yield (approx. 0.9)
η’ = yield (approx. 0.8)
Output Power (kW)
Output power Pa.
Pa = output power (kW)
Mta = output torque (Nm)
n = speed of rotation (rpm)
(For preloaded double nuts, take no-load torque into account.)
Ball Screws Permissible Loads
Permissible axial load - Double bearings
Supported each end by double bearings
Permissible axial load - Single bearings
Supported each end by single bearings
Permissible axial load - Double/single bearings
Supported each end. Double bearings one end, single bearing the other end
Permissible axial load - Double bearing one end
Supported one end only by double bearing
Ball Screws Speed & RPM
Critical speeds of ball screws
As with any rotating shaft a ball screw has a critical speed - which is it’s harmonic vibration.
Critical speed is a function of the diameter and the length of the ball screw, as well as the mounting (support) configuration. The axial clearance of the nut has no influence on the critical speed. We recommend to limit the speed to less than 80% of the critical speed.
The critical speeds are shown in the graphs below.
Critical RPM - Double bearings
Supported each end by double bearings
Critical RPM - Single bearings
Supported each end by single bearings
Critical RPM - Double/single bearings
Supported each end. Double bearings one end, single bearing the other end
Critical RPM - Double bearing one end
Supported one end only by double bearing
Axial runout
| Flange Ø | Max. axial runout |
| 16-32 | 20 |
| 32-63 | 25 |
| 63-125 | 32 |
| 125-250 | 40 |
| 250-500 | 50 |
Concentricity
| Flange Ø | Max. concentricity error |
| 16-32 | 20 |
| 32-63 | 25 |
| 63-125 | 32 |
| 125-250 | 40 |
| 250-500 | 50 |
Parallelism (for preloaded units)
Motor torque and output power
FAQs
What are Ball Screws used for?
Designed to withstand or apply high thrust loads with minimum internal friction, ball screws offer a high level of efficiency and positioning accuracy. Ball screws are very well suited for when high accuracy, precision and smooth motion is required and example applications include automotive power steering systems, wind turbines and solar panels.
Are Ball Screws Self-Locking?
Ball screws are not self-locking so a break system is required and this should always be factored in. However, ball screws are more efficient and require less torque; having lower friction and being able to run at lower temperatures also helps to reduce footprints.
Do Ball Screws have backlash?
Ball screws can sometimes experience backlash. However, this issue can be reduced significantly by preselect the ball sizing. There are also times where preloading the ball nut is effective. Please get in touch with one of our expert technical engineers for more help and guidance.
