A shedder knockout is defined as a component that acts to expel the workpiece or piece part from the die. Shedders may be activated or moved by several methods, including:

1. Pneumatics: Air cylinders or cushions
2. Hydraulics: Normally cylinders or cushions
3. Rubber pads
4. Springs
5. Through some kind of mechanical knockout

As an apprentice, learning about shedders and knockouts was extremely confusing. The main reason for that was that in most books I have read, they do a poor job of explaining that a shredder isn’t always an individual component, but can be a label for almost any component that expels the piece part. For good practice, components are normally called by their primary function name.  An example would be a spring-activated forming pad. A forming pad supports the piece part during the forming process and it also expels the part at the end of the cycle because of the spring load and the timing. So in spite of being an actual forming pad, it can also be considered a shedder or knockout.

Positive Shedder

A positive shedder can be activated, as stated before, by springs or by mechanical movement, and also by a knot or rod. These are very useful in inverted dies. There are rules when using a knockout rod, so paying close attention to the drawing is important. A knockout rod cannot be in constant contact with the shredder. It should be a minimum of 0.005in, but up to 1/64 is better in particular applications. In an inverted die, the shedder should move from 1/64th to 3/64th to have the desired effect.

When using a knockout rod, it’s good practice to have a 30° chamfer on the thrust end, to eliminate peening while providing good contact. Normally the shedder’s contour will determine the locations of the shedder flanges. Flange location should be balanced around the peripheries of the chamfer, but keep in mind how one is going to machine this and allow for grinding. A very simple and effective shedder design can be achieved using a transfer pin knockout with two nuts jammed on it with wrench flats. Using drill rod can be a good idea because it is readily available and easily and cheaply replaced, also the two jam nuts can be used to adjust the shredder.

Many shedders are coupled with shedder pins and there are two very common mistakes when using shedder pins:

1. The shedder pin placement is often misplaced in the center of the punch. Shedder pins should be placed to the side so that it also utilizes leverage in ejecting the piece part.
2. The toolmaker will make the shedder pin too short so it won’t have the appropriate length to functionally eject the work.

Shedder Activated by a Spring

In order to use a spring to activate the shedder, the spring is normally confined in the punch holder. The way it works is the spring applies pressure on the plunger, then the transfer pins transmit the shedder. The plunger must be a slip fit in the spring pocket. The tail end of the shank and of the plunger must also be a slip fit. This will be stabilizing the spring action eliminating cocking or tilting.

Conclusion

This article is a summary of the chapter on shedders and knockouts in the text that we used for the course. For more in-depth information or more detailed examples, I encourage you to look at the text. The purpose of these articles is to act as summary study aids as I am preparing for my C of Q. Thank you for taking the time to read to this article and I hope this has been helpful. Feel free to subscribe to our email to be notified of more articles as they come out.