While speed is key with most prototyping projects, taking a few minutes to consider the best way to connect your multi-piece part during the design stage could save you the hassle of having to commission the job all over.
Direct assembly with screws is a common option, but rarely a good one. Depending on the material, tapping the hole can result in worn threads in no time making your otherwise solid prototype useless. What to avoid at all costs? Self tapping or thread forming screws. These fasteners can crack or damage your prototypes before you’ve managed to even assemble it once.
Threaded brass inserts work well when the prototypes must be assembled and disassembled multiple times, keeping your part in excellent condition for as long as possible. There are two types ProtoCAM recommends for most jobs—standard or expandable—and the holes should be designed specifically to one or the other.
Standard threaded brass inserts work well with most types of prototyping materials, especially SLA prototypes, but are only held in by epoxy glue adhesive that won’t stand up to high torque applications. Recommended minimum wall thickness around the insert is 0.060”.
Expandable threaded brass inserts work great with durable prototyping materials, such as urethane castings, that will see a lot of wear and tear. These inserts are pressed into an undersized hole and as the machine screw penetrates the insert, it expands slightly. This expansion allows the insert to bite into the sidewalls, resulting in a more secure connection. Recommended minimum wall thickness around the insert is 1/2 the hole diameter, or a minimum of .060”. While these inserts provide a slightly higher pull out force when compared to the standard inserts, they still might not be suitable for high torque applications. Contact ProtoCAM and our engineering staff can make recommendations based on your specific high-torque requirements.
Choosing the correct insert for your application is just as critical as determining the right material and method. Still not sure whether standard or expandable brass inserts are best for your job? Contact ProtoCAM and we’d be happy to help.