Design Guide: Joints with Photoplastics

Photoplastics work best with thread forms designed for plastics or with snap-fits, however the design of the joint should match the mechanical properties of the material selected. 

Fastening with Metal Screws

  • When fastening with machine screws, use a metallic insert such as a hex nut, heat-set insert, or stand-off to avoid excess strain on the photoplastic.
  • Heat-set or press-fit inserts are best installed before post curing.
  • If using a thread-forming screw designed to screw into a thermoplastic material, select a tough material like xABS or xPP.


Tapping or Printing Machine Screw Threads

Avoid threads below M4 or #10 because they are likely to strip. It is preferred to print the thread form when you can, then chase with a tap if needed prior to post-cure. Plastic thread forms like those on bottle caps work well, or if using machine screw threads target sizes larger than M10 or 3/8".

Snap Fits

Snap fit connections should be designed for the material used. The snap length, thickness and interference should keep elongation below 50% the material’s strain limit.

At about 85% elongation, xPP material class works well for snap fits designed for molded polyamide.


Material Choice

Technical photoplastics with elongation below 5% should use fastening solutions designed for glass having elastomeric washers and gaskets (xCERAMIC3280, xPEEK147, or xPRO9400 FR).

Typical photoplastics with elongation in the range 5-20% are somewhat brittle and machine or fasten similar to cast acrylic. (xMODEL15, xMODEL35, etc).

Tough photoplastics with elongation in the range 20-80% (xABS3843, xPP405-Black) fasten using similar to many commodity plastics like ABS, PS, PA, PC, PS, or PP.

Elastomeric photoplastics with elongation over 100% don't work well with traditional fastening methods similar to butyl rubber.



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