What is the relationship between thread depth and thread bottom hole depth? Is there a standard?

The hole depth should refer to the bottom hole depth of the thread, and the thread depth generally refers to the effective distance of the thread. Under normal circumstances, the depth of the thread bottom hole is greater than the effective length of the thread, because there is a distance for the tool to go during the thread processing. Bm+d is the bottom hole depth, and bm+0.5d is the effective thread distance. Bm is the thread length.

Bottom hole generally refers to the diameter of prefabricated hole before tapping internal thread with tap, generally refers to the built-in round hole of workpiece, and the round hole at the bottom or top is called bottom hole. The bottom hole is not necessarily drilled, but it can be machined by other methods, such as stamping and die casting.

If the diameter of the bottom hole is the same as that of the internal thread, the tap will get stuck when the material expands, and the tap will break easily; If it is too large, the height of the tapped thread profile will be insufficient, and waste products will be formed. According to different international standards, the thread fit needs to have corresponding tolerances, so you can refer to the fitter's manual. If the bottom hole is countersunk, the influence of tapping and cutting should also be considered.

Extended data

According to the different thread rolling dies, thread rolling can be divided into thread rolling and thread rolling.

Two thread-shaped wire rolling plates are arranged oppositely, and the staggered spacing is 1/2. The static plate is fixed, and the moving plate does reciprocating linear motion parallel to the static plate. When a workpiece is fed between two plates, the moving plate moves forward to rub and press the workpiece, so that its surface is plastically deformed into a thread.

There are three kinds of thread rolling: radial thread rolling, tangential thread rolling and head thread rolling.

Radial thread rolling: two (or three) thread rolling wheels are installed on parallel shafts, and the workpiece is placed on the bracket between the two wheels, and the two wheels rotate in the same direction and at the same speed, and one of them also makes radial feed movement. The workpiece is driven by the threaded roller to rotate, and the surface is radially extruded to form threads. For some lead screws with low precision requirements, a similar method can also be used for roll forming.

Tangent wire rolling: also known as planetary wire rolling, the wire rolling tool consists of 1 rotating center wire rolling wheels and 3 fixed arc wire plates. During wire rolling, the workpiece can be continuously fed, so the productivity is higher than that of wire rolling and radial wire rolling.

Thread rolling: it is carried out on an automatic lathe and is generally used to process short threads on workpieces. There are 3 ~ 4 steel wire rollers evenly distributed around the workpiece in the rolling head. During wire rolling, the workpiece rotates, and the rolling head feeds axially to roll the workpiece into threads.

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