When screwing your prototypes together, using the proper technique is critical. Tapping the hole is an option, but the threads can wear relatively quickly in certain prototyping materials. Using self tapping or thread forming screws should be avoided with most prototyping materials, because these fasteners can crack or damage the prototypes. Threaded brass inserts work well when the prototypes must be assembled and disassembled multiple times.
ProtoCAM can assist with the installation of threaded brass inserts into our stereolithography prototypes, as well as SLS nylon prototypes, Polyjet parts, and cast urethanes. There are two types of inserts that can be used in our prototypes, standard and expandable threaded brass inserts. Choosing the correct insert for your application is critical. Please make sure the holes are designed per the tables below.
Standard Inserts 
The standard threaded brass inserts work well with all types of prototyping materials, especially SLA prototypes. The inserts are installed into the prototype with an adhesive. Keep in mind that these inserts are only held in by epoxy glue, and should not be used for high torque applications. Recommended minimum wall thickness around the insert is 0.060”. For high torque applications, it would be best to contact ProtoCAM's engineering staff for recommendations. See the chart for the design guidelines when using the standard threaded brass inserts.
Expandable Inserts
The expandable threaded brass inserts works great with durable prototyping materials, such as urethane castings. These inserts are pressed into an undersized hole. As the machine screw penetrates the insert, it expands slightly. This expansion allows the insert to bite into the sidewalls. Recommended minimum wall thickness around the insert is 1/2 the hole diameter, or a minimum of .060”. These inserts provide a slightly higher pull out force, when compared to the standard inserts. For high torque application, it would be best to contact ProtoCAM's engineering staff for recommendations. See the chart below for the design guidelines when using the expandable threaded brass inserts.
Ryan Schmidt
Engineering Manager
rschmidt@protocam.com
ProtoCAM will be exhibiting at Atlantic Design & Manufacturing tradeshow next week, June 3-5, 2008 at the Jacob K. Javits Convention Center, 655 W. 34th St. (West 34th Street at 11th Avenue), New York, NY.
