Protomold: Rapid Injection Molding
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We Reexamine Cammin’

Since 2003, Protomold has been offering the option of side actions (often called “side pulls” or “cams” or “cam actions”).  Starting with a few here and there, Protomold now produces thousands of molds with side actions each year, allowing us to mold more complex parts and support your geometry even better than before.

The purpose of side actions is to enable undercut geometry; in other words, to mold parts that could not otherwise be made in a straight-pull mold. In straight-pull injection molding, the A-Side and B-Side of the mold open and the completed part can be removed by pulling it straight out of either side. An undercut is a feature in the part design that would prevent the part from releasing out of the mold (part of the mold cavity is undercut in such a way that it grips the molded part). To release a part whose design includes undercuts, the mold surfaces that create the undercut geometry in the part must be pulled out of the part before it is ejected – otherwise the part will be stuck in the mold. A cam device in the mold is used to pull the side-action mold surfaces away from the undercut features allowing the part to be released from the mold (see Fig. 1).

Fig. 1 – Side pulls must be perpendicular to the primary (A-B Sides) pull direction.

Fig. 1 – Side pulls must be perpendicular to the primary (A-B Sides) pull direction.

Protomold produces parts using linear side actions that move perpendicular to the mold’s opening and closing axis.  Angle pins (cams) on the A-Side guide the cam carriage closer to the mold cavity on the B-side of the mold as the mold closes.  When opening the mold, the angle pin pulls the cam carriage away from the cavity and out of the part, allowing the ejector system to advance and push the part off the B-Side of the mold.

Currently, Protomold can use up to 4 side actions on a part. These side actions must be on the exterior parting line of the part, and there are some restrictions to the size of the cam feature and length of travel.  These size requirements can be found in our Reference section. Cams will increase the cost of the mold, but they also increase your design options and reduce secondary operations, thus potentially reducing the cost of your overall project.

While side actions are primarily used for forming undercuts such as holes for cables, vent holes for internal fans or slots for assembly, there are some additional applications for them such as making tall, thin parts with a core—a test tube with minimal draft, for instance.  If you were to mold a test tube using just a core and cavity (see Fig. 2), the mold might require additional draft and wall thickness to permit it to be milled and to allow for ejection.  On the other hand, if you lay the test tube down, placing the parting line down the length of the test tube (see Fig. 3) and form the inside core of the tube with a side action, you can eject the part on its side and reduce the required draft. This also allows the gate to be placed on the closed end of the test tube allowing for a uniform fill of the cavity and balanced pressure around the side action core pin.

Fig. 2

Fig. 2

Fig. 3

Fig. 3

Additional uses of side actions may include creating sharp edges on outside corners and reducing draft requirements.  You can also add text or logos to the exterior shell of your part, or add recesses for decals.  Side actions can be a valuable addition to your parts design tool chest, allowing you to produce parts with more function.

Protomold uses software that automatically helps to decide if a side action is needed for your part, and how to design it, so you need only upload a part with your desired geometry – you don’t need to know how to make a side action to take advantage of this capability. For general information on side-action cam requirements or Protomold capabilities in general, go to our design guidelines page, or call your Proto Labs account manager at 877-479-3680 with questions.



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Design Guidelines

As always, you can visit the Protomold Design Guide for helpful Rapid Injection Molding design information.

Plastics Trivia Question

POLL (Trivia will be back next month.) How familiar are you with the use of side actions in injection molding?

 A. I regularly design injection-molded parts that require side-actions.

 B. I am comfortable with design that requires side actions, but I only use it occasionally.

 C. I think I could design parts that require side-actions but I haven’t actually done so.

 D. I’m still not sure how to use side actions.

 E. I just got here. What are side actions?

Last month's question/results:
According to, how many single-serving plastic bottles of water are consumed each year in the U.S.?

A. 500 million

B. 1 billion

C. 6 billion

D. 15 billion

E. 30 billion

The correct answer is:
E. 30 billion

The responses are represented in the following chart:

Last Month's Results


Please e-mail suggested topics for future Design Tips, questions for future Designer Surveys, and obscure bits of Plastics Trivia to