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#102 Fundamentals of Press Die Structure Design (11) Relationship Between Stripper Bolt, Screw Plug, and Holes

Category : Die Design
November18, 2011

There is a very close relationship between the stripper bolts, coil springs, and screw plugs. If the hole dimensions related to the respective parts are organized, die design and fabrication become easy.

Fig. 1 summaries their details which are explained below.
The key factors in a stripper bolt are the shaft dimension (D), the head dimension (A), and the thread size (M). Considering the balance with the plate size of the die, the selection is made taking the shaft dimension and thread size of the stripper bolt as the reference. At that time, consider any coil spring diameter that is desired to be used. After that, the coil spring diameter and the screw plug dimensions are determined from the relationship with the head dimension.
It is good to make the head dimension (A) and the coil spring diameter (SP) almost the same, and it is not good to make the SP dimension large or small.
The thread pitch has been unified to 1.5 mm for screw plugs of M10 or higher. With this as the key factor, if the smallest screw plug is selected with the dimension A + 2 mm or more, it is possible to finalize the minimum relationship between the stripper bolt and the screw plug. Fig. 1 has been prepared based on this thinking. The bottom hole dimension (d2) of the screw plug has been calculated as screw plug diameter -1.5 mm (thread pitch dimension). The dimension SP has been selected to be the largest dimension that can enter in the D2 hole.

If the method of determining the relationship between the part and the hole is unified in this manner, even the related parts will be decided. The die design becomes easy if this type of relationship is organized as component units.

As precautions, it is better that the dimension of the hole (D1) in which the shaft D enters is about that shown in Fig. 1. For the shaft D, stripper bolts are available that have been ground and finished to a high accuracy. If the hole dimension is made "intermediate fit" in an attempt to make this shaft D as the guide, when the stripper bolt is tightened the shaft can butt against the hole and the movement may become hard. The reason for this is the relationship between the thread part of the stripper bolt and the tapped hole. This is a phenomenon that occurs because it is difficult to cut the tapped part vertically without any bends. It is better not to think of this method of using the stripper bolt.

[Fig. 1] Relationship between stripper bolt, screw plug, and holes

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