Nesting locators are usually the most restrictive way to locate a workpiece. These locators normally should be avoided due to their redundant location; however, for complex castings without a machined locating surface, nesting locators are sometimes the only choice.
A nesting locator either partially or completely encases the periphery of a workpiece. It may be machined, cast, or constructed with dowel pins. A machined nest, Figure 7-22, offers complete contact with the part, but is usually very difficult to make.
Cast nests are generally used for complex shapes or for nests that hold parts with irregular locating surfaces. In Figure 7-23, a nest is cast to suit the three-dimensional shape of the part. Casting a nest requires either an epoxy-resin material or a low melting point alloy. In either case, a cast nest conforms very well to even the most intricate part shapes. In addition, since the nest is cast, the time and expense involved is only a fraction of that to machine a nest.
It is generally best to make any nest separate from the tool body. The nest is then mounted to the tool body with screws and dowels. When the nest is part of the tool body, problems may result after the workholder begins to wear. If more than one nest is made at a time, the cost of replacing nests is greatly reduced. As the need arises to change the nest, a back-up nest is ready to mount on the workholder.