DLY C7 cold rolled ball screws are manufactured for general CNC, automation and industrial positioning systems that require controlled linear travel without the cost of a precision-ground screw. C7 identifies the lead accuracy grade, while cold rolling describes how the screw raceway is formed.
A C7 ball screw is commonly specified with a permissible travel deviation of approximately 0.05 mm over 300 mm of travel. This grade is widely used where stable feeding, repeatable movement and economical batch supply are required, but ultra-precise contouring or measurement-level positioning is not the primary requirement.
DLY supplies C7 cold rolled ball screws in SFU, DFU, SFE, DFI, SFI and other nut configurations. Standard models can be supplied as screw-and-nut assemblies or completed with custom length, shaft-end machining and matching ball screw supports.
C7 Accuracy Explained
C7 is an accuracy classification used to describe how closely the actual axial travel follows the nominal travel calculated from the screw lead. If a ball screw has a 5 mm lead, ten complete revolutions should theoretically produce 50 mm of linear movement. Manufacturing variation causes the actual travel to differ slightly from this theoretical value.
For a 5 mm lead ball screw, 60 revolutions correspond to 300 mm of nominal travel. A C7 screw is commonly specified with a permissible travel deviation of approximately 0.05 mm across this 300 mm interval.
The deviation is cumulative travel error, not an error added during every revolution. It describes the relationship between commanded travel and actual travel over a defined distance.
The exact inspection method, reference travel and permissible values should follow the specification confirmed for the order. Total positioning performance will also depend on axial clearance, support bearings, coupling alignment, motor control, machine rigidity, temperature and installation quality.
C7 Accuracy and Backlash
Lead accuracy and backlash describe different characteristics and should not be treated as the same specification.
Describes the difference between nominal travel and actual travel over a specified distance. It mainly affects absolute positioning over the length of the stroke.
Describes lost motion when the direction of movement reverses. It is influenced by ball size, nut matching, preload, wear and assembly condition.
A ball screw can meet C7 lead accuracy and still have measurable axial clearance. Conversely, reducing backlash does not change the original lead accuracy of the screw. Applications requiring controlled reversal error should specify both the accuracy grade and the allowable axial clearance.
C7 Accuracy and Repeatability
Repeatability describes the ability of an axis to return to the same position under the same conditions. It is possible for a machine to return consistently to one position while still having an absolute travel deviation at another position.
For this reason, a C7 value alone cannot be used as the complete repeatability specification of a machine. Repeatability is also affected by direction reversal, motor resolution, control settings, bearing rigidity, thermal change, guideway condition and external load.
When the machine requires accurate movement between multiple absolute positions, the complete positioning-error budget should be evaluated rather than relying only on the ball screw grade.
Cold Rolling Process
During cold rolling, hardened forming dies apply pressure to the screw blank and plastically form the helical raceway. Material is displaced into the required profile instead of being removed by a grinding wheel.
Rolling allows standard diameters and leads to be produced efficiently and consistently. This makes C7 cold rolled ball screws practical for repeat orders, replacement supply and batch production of industrial equipment.
After raceway forming, the screw passes through subsequent operations such as heat treatment, straightening, surface finishing, nut matching and inspection. Shaft ends can then be machined according to the bearing and motor connection drawing.
DLY C7 Cold Rolled Product Range
The C7 grade is available across different DLY nut structures. The suitable series should be selected according to installation space, lead, axial clearance, rigidity and load requirements rather than accuracy grade alone.
| Series | Nut Structure | Primary Selection Reason |
|---|---|---|
| SFU | Standard flanged single nut | Common dimensions, broad model availability and general industrial use |
| DFU | Flanged double nut | Greater axial rigidity and more controlled backlash |
| SFE | Compact flanged single nut | Large-lead configurations for rapid linear movement |
| DFI | Flanged double nut | Stable reversal performance where installation space permits a longer nut |
| SFI | Internal-circulation flanged nut | Compact circulation structure and controlled nut dimensions |
| SCI / SCM | Cylindrical nut configurations | Integration into custom nut housings and space-limited mechanisms |
Common DLY cold rolled specifications include 4 mm, 5 mm, 10 mm and larger leads depending on the selected series and diameter. Model availability, nut dimensions and load ratings must be confirmed against the corresponding specification sheet.
Suitable Applications
C7 cold rolled ball screws are suitable when the equipment requires practical positioning performance, efficient transmission and controlled purchasing cost. Typical application conditions include:
Applications Requiring Higher Accuracy
C7 should not be selected automatically for every positioning axis. Higher-accuracy applications may require a ground C5, C3 or higher-grade ball screw, depending on the travel length and permissible positioning error.
A higher grade should be evaluated for applications such as:
- Precision grinding and high-accuracy machine tool feed axes
- Coordinate measurement and dimensional inspection equipment
- Semiconductor positioning and precision alignment systems
- Fine-pitch winding or dispensing with strict absolute-position control
- Long-stroke axes with a small total positioning-error allowance
- Machines without external position feedback where screw lead error directly determines accuracy
Frequently Asked Questions
Q: Does C7 mean the ball screw has 0.05 mm backlash?
A: No. The approximately 0.05 mm per 300 mm value describes permissible travel deviation, not axial backlash. Backlash is a separate specification related to lost motion during direction reversal.
Q: Is C7 accuracy the same as machine repeatability?
A: No. C7 describes ball screw lead accuracy. Machine repeatability also depends on axial clearance, support bearings, motor control, guideways, load, temperature and assembly rigidity.
Q: Can a C7 ball screw be used in a CNC machine?
A: Yes. C7 cold rolled ball screws are commonly used in CNC routers, engraving machines, woodworking machines and general feed axes. Precision machining centers or inspection equipment may require a higher accuracy grade.
Q: Can lead error be compensated by the controller?
A: Some control systems can use measured error maps or closed-loop position feedback to reduce absolute positioning error. Compensation does not remove axial clearance, elastic deformation, thermal expansion or installation error, so the mechanical system must still meet the basic performance requirements.
Q: Can the shaft ends be machined before delivery?
A: Yes. Bearing seats, coupling ends, external threads, shoulders, retaining-ring grooves and keyways can be produced according to an approved drawing.
Q: What is the minimum order quantity?
A: Standard C7 models can generally be ordered from one piece. Customized products may require a higher minimum order quantity, which must be confirmed according to the model, length and machining process.
Send the ball screw model, quantity, length, required travel accuracy and shaft-end drawing. DLY will confirm the suitable nut series, processing requirements and matching support units.
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