Threaded connection is one of the most widely used disassembly connection methods in mechanical devices.
However, after long-term use, inevitable wear and damage will occur. So, how to repair the damaged threads?
This article will provide a detailed explanation of the method of re-threading the threads.
I. Basic Principle Analysis of Thread Retracting
The main method of thread retraction is to use a special tool for single-point cutting to repair the misalignment
of the damaged thread surface. By performing directional cutting to remove the height difference at the peak,
the uneven horizontal plane of the thread is restored to its original state.
Unlike complete reprocessing, thread regrinding only makes local corrections on the existing structure
without altering the effectiveness of the thread. Therefore, only the cutting amount needs to be controlled,
and after 1 to 2 regrindings, it can be restored for use.
II. Key Steps for Thread Retracting Operation
The key points for the thread retraction operation lie in selecting the appropriate thread cutting tool
and cutting parameters. Here, we recommend using a 60° sintered tool with guiding teeth or a dedicated thread
retraction tool. The tool material can be HSS or hard alloy.
When turning the teeth, the spindle speed should be controlled within 25-35 m/min. The single cutting depth should
not exceed 0.2mm. Every 2-3 threads, the cutting should be stopped for one time and then reversed for cutting.
The workpiece must be locked at each stage.
By repeating the cutting process multiple times, the difference in the height of the threads can be corrected.
However, be sure not to over-cut, as excessive reduction in the thread fit can cause the rotation to become too tight.
III. Strategies for restoring threads in different damage situations
For threads with local surface abrasion, the above conventional methods can be directly used for restoration.
However, for severely deformed threads, the conventional methods are ineffective. In such cases, it is necessary
to pre-process the locating holes, which is also known as "filling teeth".
At the most severely damaged threaded top notch, first drill a positioning hole and thread it, then re-carve it using
a reaming tool for cutting and repair. This method has a higher success rate.
However, the operational difficulty is also increased.
IV. Precautions for Thread Reaming
During the thread reaming process, it is strictly prohibited to use coolant. Otherwise, it is very likely to cause metal
residue and reduce the surface quality. Dry cutting must be carried out.
Also, closely monitor the thermal deformation of the workpiece. If it gets too hot, it will be difficult to control
the reaming process. At this point, you should stop the cutting, reset the machine, and then continue.
Remember not to remove too much at once.
Finally, for severely damaged threads that cannot be repaired using conventional methods, it is not recommended
to force the re-threading. This would waste a lot of time. The more economical option is to directly replace
the new threaded components. This article systematically analyzes the method of thread retraction,
providing it as a reference for those in need. We hope it can achieve twice the result with half the effort.
