Technical Tutorial - Low cost automation

Preplanning To Prevent Thread Damages

The following are the common cases of screw thread damages.

(1) Common cases of thread damages

• Threaded hole side: In case where assembly and disassembly are frequently repeated, the entry portion of the thread may be damaged and the screws may become difficult to start. When this occurs, use a tap to clean the damaged portion of the thread so the new thread will be smoothly connected to the existing portion of the thread. If a bolt is forced into the damaged thread, the deeper portion of the thread is further damaged and the entire tapped hole may become stripped.
• Bolt side: When a bolt is tightened with a nut, inadvertent object strike on the exposed thread portion of the bolt may crush and damage the thread. This would make the machine impossible to be disassembled.

(2) Small trick in avoiding thread damages

Threaded holes (see Fig. 1)

• Chamfer the entry hole opening so the bolt will enter perpendicularly tothe hole.
• This can be done with sufficient results by touching-off the entry hole with a drill slightly larger than the female thread size.
• Take extra care in specifying the drawing notations if the material to be machined is soft (aluminum and non-hardened steel).

Bolt side (see Fig. 2)

• Grind and smooth away the threads exposed beyond the nut.
• Machine the bolt prior to use so the unneeded thread portion is removed.
• Do not use unnecessarily long bolts.