I need to design a simple thrust bearing to support a vertical load. I want to keep the diameter as small as practical, ideally about 3/8 inch or less. The static load will be up to 500 pounds, and the speed of rotation will be around 4 RPM, but the shaft will only rotate 180 degrees and stop for a while, then rotate back 180 degrees. The number of rotations per day will likely be around 10, so 40,000 cycles would probably last 10 years. Initial lubrication can be performed (high pressure grease?), but periodic lubrication is not feasible. The working environment should be reasonably clean, but it may collect some dust over time as it will not be fully sealed unless required.
I am considering a single hardened bearing ball in a Delrin spherical socket. If my calculations are correct, a ball of diameter 1/4 inch with a contact area of about 50% of the sphere would have a surface area of about 0.2 in^2. Delrin has a Young's modulus of 450,000 PSI. Based on these criteria the force of 500 pounds on the ball should produce a pressure of about 2546 PSI. This is far under the yield strength of Delrin. Am I missing something here? I have not been able to find anything on designing such a simple thrust bearing. Attached is a CAD model showing the concept.