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The thread hole is not deep enough after processing. How to repair it?

2019/3/28 11:17:37 Viewers:
In the process of tapping threads on workpieces in the mechanical processing industry, there are many factors that cause threads on some workpieces, such as unreasonable technology (workpieces with processed threaded holes are processed after welding), faulty reading of drawings (wrong size) or misoperation (calculation error, shallow bottom hole drilling, programming error and depth positioning error of drilling threaded holes). The hole is not deep enough after processing.

Once such problems occur, due to the poor stability of the drilling machine, operators and technicians often install the workpiece to be repaired on the boring machine or milling machine workbench directly. After calibration and fastening, the bottom hole of the threaded hole is drilled to the drawing depth according to the internal diameter of the threaded hole, and then the threaded hole is repaired with the tap. But this method can easily cause the operator to "friction cutting" the original thread in the process of deepening the drilling bottom hole, resulting in the destruction of existing threads and affecting the processing quality of threaded holes.

At the same time, this repair method requires the operator to have a good technical level, and the thread hole correction process takes a long time, and the work efficiency is very low. The cost of using boring and milling equipment to repair it is also relatively high. In addition, if the end face of threaded hole is not perpendicular to the center line of the threaded hole due to the welding process or other reasons, it will inevitably lead to the destruction of the existing threads in the process of secondary drilling threaded bottom hole, which will inevitably lead to the hidden danger of scrap or degradation of the workpiece threaded hole. After many discussions and experiments, the author has found a series of tips which are fast in work efficiency, reliable and stable in quality.

Method of Repairing Shallow Thread Hole on Rocker Drilling Machine

If the material hardness of the workpiece is high, it can be drilled on the rocker drill to repair the threaded hole. However, the center line of the threaded hole should be corrected parallel to the center line of the drilling machine spindle in the way shown in Fig. 1. Then the center line of the threaded hole and the drilling shaft of the drilling machine should be corrected directly with the drill bit, and the shallow threaded hole should be drilled with the drill bit and tap according to the required size. 

Firstly, the workpiece is placed on the adjustable screw arranged on the drilling machine table; secondly, the correcting screw is screwed into the thread hole to be repaired and tightened to ensure that the centerline of the correcting screw is consistent with the centerline of the threaded hole; secondly, the drilling machine spindle is close to the correcting screw (clearance must be kept to prevent the drilling machine spindle from extruding the correcting screw and affecting the correcting accuracy). The adjustable screw is adjusted to make the correcting screw parallel to the main shaft of the drilling machine and gradually adjust and lean to ensure that the parallelism error is not more than 0.03mm. A piece of paper can be used to pull the upper and lower parts between the main shaft of the drilling machine and the correcting screw to make the force uniform. Finally, the drill chuck is installed in the main shaft of the drilling machine, and the modified drill bit is clamped in the drill chuck to insert the drill bit into the screw to be repaired. In the threaded hole, after observing that the clearance between the handle and the threaded hole is uniform, drill according to the required size, and replace the tap tapping screw after drilling.

The manufacture of the modified bit is very simple. The length of the drill edge of the old bit can be grinded to enough. The straight shank part of the drill is uniformly ground or trucked to 1 mm, so that there is a 1 mm gap between the drill hole and the original thread hole, and no damage to the existing thread hole will occur.

The accuracy of the correcting screw is required to be high. The threaded part of the screw must be coaxial with the straight handle part, and there must be no bending. The length of the correcting screw is generally 3-5 times of the depth of the thread to be repaired, so as to ensure the correcting accuracy.

2. Method of Repairing Shallow Thread Hole with Pistol Drill

For larger, heavier and softer workpieces (such as aluminium alloy workpieces) which need to repair the shallow depth of threaded holes with smaller diameter and size, a pistol drill can be used to hold the aforementioned modified drill bit and drill it directly, and then tap the threads manually (see figure 2). 

Three. Conclusion

The method of repairing small threaded holes is very innovative, especially the use of old drill truck and modified drill after grinding, which is a small invention. It not only reuses waste materials, but also solves the more difficult and real problems in the industry. In the actual production process, it can effectively solve the problem of repair of shallow threaded holes. The method is simple, practical, and can be popularized. It is worth popularizing.