What are the requirements for the accuracy of products when we process self-locking tuning screws?

The machining accuracy of the self-locking tuning screw directly affects the locking reliability, tuning stability and assembly adaptability. The core requirements focus on four dimensions: dimensional accuracy, form and position tolerance, thread quality and self-locking function parameters. The specific standards are as follows:

First, the core size accuracy requirements (key adaptation indicators)

Thread related dimensions:

Thread specifications (such as M2, M3, M4, etc.) shall conform to corresponding standards (such as ISO 898), and the pitch diameter tolerance shall be controlled at IT6-IT8 level (for example, the pitch diameter tolerance of M3 screw is ±0.015~±0.025mm) to ensure accurate engagement with nuts/threaded holes.

Pitch error ≤±0.01mm (within 25mm length), so as to avoid tuning jamming or self-locking failure caused by pitch error.

Rod and head size:

The rod diameter tolerance is ±0.01~±0.03mm (adjusted according to the screw specification), so as to ensure the fit with the clearance of the assembly hole (usually the clearance is ≤0.05mm).

The tolerance of head thickness and opposite width (or hexagon size) is ±0.02~±0.04mm, so as to ensure smooth bite of tools and no slippage when tightening.

Total length tolerance:

The tolerance of normal length (5~50mm) is ±0.03~±0.08mm, and the tolerance of long screw (> 50 mm) is ≤±0.1mm, which meets the precise control of tuning stroke.

Second, the form and position tolerance requirements (to ensure the accuracy of assembly and movement)

Straightness: the straightness error of the rod is ≤0.02mm/m, so as to avoid assembly sticking caused by bending or uneven stress during tuning.

Verticality: the verticality error between the head and the rod is ≤0.03mm (within 10mm length), so as to ensure the uniform stress during tightening and prevent the thread from eccentric load wear.

Coaxiality: the coaxiality error between the threaded part and the rod part is ≤0.02mm, so as to ensure smooth thread engagement and no offset jamming during tuning.

End-face runout: the end-face runout of the head is ≤0.02mm, so as to avoid that the head does not fit tightly after tightening, which will affect the self-locking stability.

Three, thread quality and precision of self-locking function (core performance index)

Thread surface quality:

The thread profile is complete, without tooth collapse, burr and scratch, and the surface roughness ra is less than or equal to 0.8 μ m, which reduces the friction resistance during meshing and ensures smooth tuning.

The difference between the single pitch diameter of the thread and the virtual pitch diameter is ≤0.015mm, so as to avoid the instability of self-locking force caused by tooth profile distortion.

Self-locking function parameters:

Self-locking torque: Set the range according to the product specifications (for example, the self-locking torque of M3 screw is 5 ~ 15 ncm), and the torque fluctuation of the same batch is ≤ 20%, so as to ensure that it will not loosen after locking.

Tuning repeatability: After multiple tuning (≥10 times), the screw positioning accuracy deviation is ≤±0.01mm, which meets the requirements of precise tuning scenes (such as electronic equipment and instruments).

Anti-loosening performance: after vibration test (such as 10~50Hz vibration for 30min), the screw does not loosen and the thread engagement gap does not increase obviously.

Four, the surface and material accuracy requirements (to ensure durability)

Surface treatment accuracy:

The coating thickness is uniform (for example, the thickness of galvanized coating is 8~12μm), with a tolerance of 1 μ m, without missing plating and peeling, so as to avoid thread sticking caused by uneven coating.

The surface hardness reaches the standard (such as HRC35~45 after heat treatment), and the hardness uniformity deviation is less than or equal to ≤3HRC to prevent deformation or wear in use.

Material consistency:

High-strength alloy materials (such as stainless steel 304/316 and carbon steel 45#) are selected, and the material composition meets the standards, and there are no defects such as impurities and pores, so as to ensure the stable mechanical properties.

V. Additional requirements for special scenes

High-frequency tuning scene: the reciprocating tuning life of the screw is ≥1000 times, the thread wear is ≤0.01mm, and the self-locking performance has no obvious attenuation.

Micro screw (≤M2): the dimensional tolerance is tightened to ±0.005~±0.015mm, and the shape and position tolerance is ≤0.01mm, which is suitable for the assembly space of precision electronic equipment.