September 2004 Design Tip

Simply Side Actions

In case you haven't heard, rapid injection moulding can now support simple undercuts in your part design. The details of what we mean by a "simple undercut" can be found in an updated version of the Protomold Design Guide, but in summary our definition of a "simple undercut" is as follows:

1) It is on the outside of the part geometry - not the inside.
2) It is on the parting line.
3) It fits within certain size constraints (see below).


A side action used to create
a through-hole undercut feature

As you are probably aware, undercuts in your part design are implemented through the use of what are called "side actions" in the mould. The animation to the right illustrates how a side action can be used to implement a through-hole type of undercut, and the following table describes the maximum dimensions of the side actions that the Protomold process can currently support.

Width Height Pull
≤ 3.188 in ≤ 1.640 in
≤ 1.140 in
≤ 0.640 in
≤ 1.500 in
≤ 1.700 in
≤ 1.800 in
Size constraints for mould side actions

Due to mould size constraints we can have up to two side actions per part. As always, your ProtoQuote® will identify an undercut and let you know whether or not a side action can be used to accommodate it.

However, we can handle some pretty interesting geometries within these constraints (see illustration), so feel free to leave in some of those undercuts in your next part design.


Example double undercut part courtesy of Vascular Solutions, Inc.

You can visit the Protomold Design Guide for other helpful Rapid Injection Moulding design information.