How might a PhD-holding physicist submit independent research after leaving academia, without appearing to be a crackpot? There is a no dearth of crackpottery in the world of amateur physics research, nor in the world of independent research done by PhD-holding physicists. If I want to continue physics research in my own time after graduating and moving on to industry, what would be the best way to share my research with the physics community?
Actually, you just write and submit papers just as if you were in academia. They will be reviewed in the normal way and published if they are seen to have merit. But if the reviewers tell you that you are a crackpot, then try hard to come up with better (or more acceptable) ideas. 

But I think that physics research must be pretty hard without labs and a circle of collaborators, etc, that you find in academia. Theory can, perhaps, be done while you are a functionary in the Patent Office, but you need to stand out to make a name. 

But if you have a supportive advisor you can, perhaps, get connected to a research group and work with them even though not employed. 

But don't publish your work in venues normally associated with crackpots.