Cam-Out and Screw Breakage in Micro-Screws: Causes and Prevention

In the assembly and removal of micro-screws, cam-out (a stripped recess) and screw breakage are the two most common and most expensive failure modes. Both appear to happen "in that instant," but their causes are usually laid down well before the motion begins. Breaking the causes into layers is more valuable than post-hoc repair.

Layer one: mismatch between recess and bit. Phillips, Pozidriv and Torx recesses each have a standard head angle and depth. Choose the wrong bit type, or let a bit wear, and the contact area shrinks quickly. A smaller contact area multiplies the pressure on the recess wall at the same torque, so a damaged recess is only a matter of time. This is the most easily avoided and most frequently overlooked cause.

Layer two: torque settings disconnected from actual need. Tightening torque and removal torque are not symmetrical. Long-term tightening, thread-locking adhesive and oxidised plating all push the torque actually required above the assembly value; if the bit is still backed out at assembly torque, it either slips or grinds the recess away through repeated attempts. Conversely, setting the torque too high can shear the screw neck outright — especially below M1.0.

Layer three: coaxiality and perpendicularity error. Applying torque before the bit has seated accurately in the recess centre concentrates force on one side of the recess, a classic trigger for cam-out. The larger the offset, the sooner it happens. This is also why an automatic vision screw removal machine earns its keep in micro-screw work.

Layer four: repeated operations, heat and adhesive. Turning the same screw repeatedly gradually wears the recess wall; with adhesive-coated screws, spinning at full speed first lets the adhesive's reaction force kick the bit out of the recess. Correct practice is to locate at low speed first and then back out at the set torque, rather than going full speed from the start.

Layer five: what makes breakage special. Breakage usually occurs at the screw neck and relates to material, thread length and torque peaks. Notably, cam-out is often the precursor to breakage — once the recess is stripped, operators tend to press harder, transferring torque from the recess to the screw body and eventually shearing it. Stopping cam-out is therefore also preventing breakage.

Prevention checklist (usable for daily checks): - Record bits by recess type and size; replace on measured wear rather than after damage; - Set removal torque independently, support multi-stage torque and angle monitoring, and stop on anomaly; - Prefer vision alignment over hard mechanical referencing, allowing a range of placement deviation; - Lower the torque ceiling for thin-wall parts and small sizes, protecting the workpiece first; - For adhesive-coated screws, follow "locate at low speed, then back out at set torque"; - Use dedicated extraction tools for already-stripped screws instead of repeated forcing.

Relationship to the machine. Of those six items, four can be covered directly by machine capability: multi-stage torque setting, angle monitoring, vision alignment and anomaly stop. Choosing small screw removal equipment with those capabilities is itself the most direct layer of prevention. Conversely, if the machine offers only a single torque stage and no angle feedback, operator experience becomes the only line of defence — which is not reliable on lines with high staff turnover.

Shenzhen Honred Technology provides non-standard custom solutions for automatic screw driving and combined drive-and-remove equipment. Its vision fastening and M0.8-M2.0 screw removal solution cover multi-stage torque setting, angle monitoring and vision alignment, helping lines move cam-out and breakage prevention from "relying on experience" to "relying on machine capability."