In the process of tapping threads on workpieces in the mechanical processing industry, sometimes problems arise due to unreasonable processes (the workpiece with threaded holes is welded and then the threaded hole end face is processed), the processing personnel make mistakes in reading the drawing (wrong size) or operational errors. (Calculation errors, drilling shallow bottom holes, programming errors, and incorrect depth positioning of threaded holes) and many other factors lead to the phenomenon that the threaded holes on some workpieces are not deep enough after processing is completed.
Once such problems occur, due to the poor stability of the drilling machine, operators and process technicians often directly install the workpiece with the threaded hole to be repaired on the boring machine or milling machine workbench. After correction and tightening, the threaded hole bottom hole drill bit is used according to the After the inner diameter of the threaded hole is corrected, drill the bottom hole to the depth of the pattern, and then use a tap to repair the thread. However, this method can easily cause the operator to "frictionally cut" the original thread during the process of deepening the bottom hole, causing damage to the existing thread and affecting the processing quality of the threaded hole.
At the same time, this repair method requires the operator to have a good technical level, and the threaded hole correction process takes a long time and the work efficiency is very low. The cost of repairing it with boring and milling equipment is also relatively high. In addition, if the end face of the threaded hole is not perpendicular to the centerline of the threaded hole due to reprocessing after welding or other reasons, it will inevitably cause damage to the existing threads during the secondary drilling of the threaded bottom hole. , which will inevitably lead to the hidden danger of scrapping or downgrading the threaded hole of the workpiece. After many discussions and experiments, the author found a series of tips that are more efficient, reliable and stable in quality.
1. How to repair shallow threaded holes on a radial drilling machine
If the workpiece material is of high hardness, you can drill and tap it on a radial drilling machine when repairing its threaded holes. However, it is necessary to first correct the center line of the threaded hole to be parallel to the center line of the spindle of the drilling machine as shown in Figure 1, and then directly use a drill to correct the coaxiality of the center line of the threaded hole and the drill shaft of the drilling machine, and use a drill bit and a tap to meet the required dimensions. Drill and tap shallow-depth threaded holes.
Steps to repair the threaded hole: First, place the workpiece on the adjustable screw that has been arranged on the drilling machine workbench; secondly, screw the correction screw into the threaded hole to be repaired and tighten it to ensure that the center line of the correction screw is in line with the threaded hole to be repaired. The center lines of the threaded holes are consistent; then, bring the spindle of the drilling machine close to the correction screw (a gap must be left to prevent the spindle of the drilling machine from squeezing the correction screw and affecting the correction accuracy), and adjust the adjustable screw so that the correction screw is parallel to the spindle of the drilling machine. , gradually adjust it gradually to ensure that its parallelism error is not greater than 0.03mm. You can use a piece of paper to pull the upper and lower parts between the drill machine spindle and the correction screw to make it evenly stressed; finally, remove the drill chuck. Install it in the spindle of the drilling machine, clamp the modified drill bit in the drill chuck, insert the drill bit into the threaded hole to be repaired, observe that the clearance between its handle and the threaded hole is uniform, drill according to the required size, and complete the drilling. After drilling the hole, replace it with a tap and tap the screw.
The production of modified drill bits is very simple. Just grind the blade length of an old drill bit as long as possible. The straight shank part is evenly ground or turned away by 1mm, so that there is a 1mm gap between the original threaded hole and the threaded hole during drilling, so that no damage to the existing threads of the threaded hole will occur.
The accuracy requirements of the correction screw are relatively high. The threaded part must be coaxial with the straight shank part and must not be bent. Its length is generally 3 to 5 times the depth of the thread to be repaired to ensure correction accuracy.
2. How to repair shallow threaded holes with a pistol drill
For larger, heavier and softer workpieces (such as aluminum alloy workpieces) that need to repair the problem of shallow threaded holes with smaller diameters, a pistol drill can be used to hold the aforementioned modified drill bit and drill it directly. , and then tap the thread manually (see Figure 2).
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3. Conclusion
The method of repairing small threaded holes is very innovative, especially the use of modified drill bits that are turned and ground from old drill bits. It is really a small invention that not only reuses waste materials, but also solves a difficult but real problem in the industry. The problem. In the actual production process, the problem of repairing shallow threaded holes can be effectively solved. The method is simple, practical, and can be popularized.
