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 pin restricts motion along 1 axis, or 2 degrees of freedom,
like a round pin in a slot.
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 movements 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 in locating,
select a pin with a tapered or bullet nose.
These can be used when locating radially
as the chances for binding is increased significantly
when attempting to use 2 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 minimizing or eliminating tolerance stack-up,
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 stack-up 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 into the next episode for more on locating pin mounting types.