Locating Pins Pt. 2: Types of Locating | Engineer to Engineer | MISUMI USA

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Locating Pins Pt. 2: Types of Locating | Engineer to Engineer | MISUMI USA

Locating pins are used in workholding fixtures and jigs to secure workpieces during the production of parts. If you’re new to workholding concepts, check out our first episode for an introduction to the basics. This episode will take a look at the main types of locating pins, head shapes, and the primary uses for each one.

There are two classifications of locating pins, 2-way and 4-way. A simple method to remember the difference between them is to consider the 3 axes of translational motion, and the 6 corresponding directions or Degrees of Freedom. A 2-way locating pin restricts motion along 1 axis (or 2 degrees of Freedom), like a round pin in a slot [show example]. Likewise, a 4-way pin restricts 4 degrees of freedom along 2 axes. A round locating pin located concentrically in a hole is a common application of a 4-way pin, and helps to further secure the piece. In order to sufficiently locate a part, a minimum of one of each type of pin is required to prevent excess motion of the workpiece, and more locating components may be used as needed.

Depending on the application, 4 common head shapes provide options to a fixture designer when selecting locating pins.

The most basic type of locating pin head shape is the flat nose, and as such, is used for the most basic type of locating: uni-directional external surface locating. This is effective at limiting movement using straight edges on the pin’s side or on the top (as a way to position a surface to a specific height). These may also provide lateral guidance when sliding a part onto a fixture, and can be used in conjunction with a datum edge to ensure correct positioning. The main disadvantage of this locating pin head type is its lack of versatility… drop-down concentric locating is not recommended as the sharp corners and tight tolerances can damage the workpiece in some cases.

In order to prevent binding when locating, select a pin with a tapered or bullet nose. This can be used when locating radially, as the chances for binding is increased significantly when attempting to use two round pins.

While tapered and bullet nose pins help prevent binding, changing to a spherical locating pin head can prevent or minimize the possibility of damage to the part when locating by drop down method.

Finally, locating pins with a diamond head shape allow for additional clearance on one side compared to a round pin. This is useful in eliminating or minimizing tolerance stacking, especially when combined with a round pin for radial or concentric locating applications.

A key component in industrial automation, locating pins are a great tool when designing a jig or fixture. Whether locating on an edge with a flat nose pin, avoiding tolerance stacking by using a diamond pin, reducing binding with a bullet-nose head, or preventing workpiece damage with a spherical tip, each head shape and pin type serves its purpose. Tune in to the next episode for more on locating pin mounting types.

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Locating Pins Pt. 2: Types of Locating | Engineer to Engineer | MISUMI USA