Because something has to arrest the strip!

Purpose of Die Stops

The main purpose of a die stop is to stop the feeding movement or advancement of the stock strip. Just keep in mind that we have discussed similar components like pilots, may also arresting the feed of the stock.

Basic Stop Principles

There are two definitions associated with the fundamental principles of a stop:

1. Stop position: This is where the surface of the stock strip is stopped or the actual location or stopping point of the strip.
2. Register position: This is the exact location where the stock strip must stop to achieve a good part meeting all dimensional requirements. The registry position may or may not be the same as the stopping position, according to the text.

Stops may act as gauges in some applications. In other situations, the stop acts more like an approximation gauge and the pilot does the actual registry of the part. This was a difficult concept for me to grasp as I don’t work in a tool and die shop making stamping dies, instead we maintain moulds. The concept is that there is a time when the work may be registered by a pilot or a component acting as a pilot. When a stop acts as a  true gauge, then the stop and registry positions are one and the same.  Stops and pilots are basic concepts or tools for a toolmaker that are used to arrest the work strip. In many cases, there is a difference in feed distance or a strip is allowed to travel more or less than the progression because of the kind of pilots used. This is called overfeed.

Optimum Overfeed

Overfeed is the difference between the stop positions and registry positions.  

There are two major factors that determine optimal overfeed and they are interrelated.

1. Pilot size
2. Thickness and hardness of the stop

This is a general rule, but small pilots require a minimum of overfeeding. This is the same for light material, and generally, the rule states that with large pilots and heavier stock the overfeed travel increases.

There is something to keep in mind other than primary stops, automatic press feeds eliminate the need for stops. So all this article info depends on the feed being used.

Stop Categories

There are three categories for stops and they are mostly self-explanatory, they are:

1. Primary
2. Secondary
3. Final

The primary is the first stop and called primary because it acts as a true gauge and registers the stock strip. Their secondary stops are more of approximation gauges and final stops may or may not register the strip.

Stop Type

There are several stop types and even more variations on each type, so the rest of this article will be a very general description of some types and their applications or build qualities. These parts of the article may grow in time so please feel free to come back if this interests you.

Solid Stops

This is really as the name sounds. Solid stops are a block of metal machined and located to stop the piece part before maybe a bend operation. Sometimes a solid stop, because it is a block, will have other features or components machined into it, such as retaining a spring. The text does make a point to state that solid stops may be made hardened for 3 reasons:

1. Their process of feeding the stock strip and arresting it can wear or erode the stop location changing the accuracy.
2. Stops experience friction from the motion of the spring pad.
3. Solid stops often also act as a thrust block and experience very high forces during the motion of the chop off the punch.

Some variations on solid stops are solid stops mounted on a hardened die block, end mounted solid stops and adjustable solid stops. These are better explained using graphics that I may add.

Plain Pin Stops

Just as the name suggests these are one of the simplest types of die stops. This stop is just a plain cylindrical pin sometimes even a readily available dowel.  The pin is mounted in an accurately placed hole in the die shoe or component. Clearance should be provided for pin type stops.

There are 3 reasons for this:

1. To allow the height of the pin stop to be adjusted without having to remove the die shoe.
2. To allow ease of pin removal for punch sharpening.
3. To allow the pin to be driven down if there is a misfeed thus reducing damage to the die.

Headed Pin Stops

Headed pin stops are a variation on a pin-type when the stop is close to a die edge. Using this style of pin stop allows the location hole to be a safe distance from the die edge, but the effective arrest location is achieved.

Disappearing Pin

Just like the name suggests, the pin will disappear into the die as it cycles down. This type of pin normally sits on a spring that allows it to move into the die. One advantage of this kind of pin is that starting an opposite clearance hole is not necessary.

Finger Stops

Finger stops almost look like a pusher with a coil spring. They can be quite simple or very complex depending on if they are activated. There are many variations on finger stops and material requirements.

Pivoted Auto Stops

The pivoted auto stop is a little more complex than even a finger stop as they have multiple components and are also normally timed for the pivoting action.  A pivoted auto stop assembly consists of the stop, pivot pin, spring, and an activator or tripper.  Pivoted stops operate by having the die action as it descends before the tripper contacts the stop, the tripper is tripped to pivot the stop in order to arrest the strip having a double action. The tripper mechanism at the time can be quite elaborate with several variations depending on the application.

Conclusion

The text has several variations and types of stops that I do not mention at this point, simply because these articles are summaries of the chapters that I am using to prepare for my C of Q test. If you’re interested in a more in-depth reading on the topic, I encourage you to get the text. If you liked what you just read, please share and if you want more subscribe to our mailing list.