Read Part 1 of this project here
To recap, Delrin, Nylon, HDPE and a host of other engineered plastics can already be found in various places on many experimental aircraft. For the more adventurous among us, ABS, PETG, and even PLA are also being utilized where applicable and possible.
While I am a huge fan of Delrin, recently ABS and PETG have absorbed the bulk of my plastic component needs due to one simple reason: I can 3D print it rather than have to CNC it. 3D printing is far quicker, easier and often cheaper for short-run production needs than traditional CNC techniques.
In part 1 I set out to determine if I could successfully design a replacement for Delrin for low-heat low-load high-friction applications with PETG or ABS. In this instance, I set out to utilize a 3D printed wear surface to replace my torque tube cap.
Note the AN4 bolts securing the red torque tube cap in the below image:
The subsequent 3D model designed to replace the above 4130 part:
To provide ample safety margin, rather than rely on the layer adhesion strength of PETG to retain structural integrity (which is quite high when compared to other 3D printed plastics), I incorporated 6061 aluminum inserts and cap. This aluminum load bearing structure allows for an (unlikely) catastrophic failure of the PETG without serious consequence to the pilot or craft. This inclusion of aluminum allows for the 3D printed part to act simply as a wear surface while still being quick and inexpensive to fabricate.
Red is 3D printed PETG plastic, pressed aluminum inserts and cap are machined 6061:
Installed:
Initial Impressions
Other than the normal lubrication requirements, the tried and true 4130 torque tube cap has served Cubs well since the 1930s. That said, it is a metal on metal bearing surface often utilizes washers to set the tube compressive forces, and for many (including me) resulted in a very sloppy tolerance. My new plastic wear surface conforms to the torque tube with much tighter tolerances and the control stick sloppy feel was immediately improved with installation. If this were a Delrin part I might not even lubricate it (Delrin is an amazing material), however until the full characteristics of the PETG are understood in this application I am utilizing the aviation standard LPS 1 silicone lubricant on the internal diameter plastic wear surface.
I will check for abnormalities every 10 hours until satisfied, however the short initial testing results have been positive thus far.