I made the rocking chair in the picture about 20 years ago. It's not quite right comfort-wise, and I threw away the jigs years ago. I now want to make another one, and am having a bit of a job with the ergonomics. Does anyone have any knowledge/ideas regarding the basics, like the angle of seat to back, etc?
Thanks for looking!
Always good to see someone tackling a chair. The bible for the ergonomics of chair and furniture design is Human Dimension & Interior Space by Panero and Zelnick.
The standards for office or dining chairs (ie chairs where you need to remain alert when seated) are that the seat itself slopes backward 2-5 degrees, and the back is at 95-105 degrees to the seat. However an easy chair can slope back much further.
But rocking chairs tend to be special cases, in that as well as the question of comfort you also have the practical issues of getting in and out of the chair. Ideally you want the chair to recline quite a lot for relaxation, but to swing more upright when the sitter leans forward to allow them to get out of the rocker without facing the classic dilemma of being "trapped in a deck chair"!
I was at a workshop when this particular rocker was first being developed,
The chosen solution to the dilemma was in the shape of the rocker, it didn't conform to an arc of a circle, instead the curve changed radius throughout its length.
Best rocking chairs ever made were the Thonet. I know this from having one. Very relaxing - even the heel bar is exactly right for rocking it with just a twitch of your big toe. The geometry is perfect compared to others I've tried, including a posh Swedish job.
You could copy the basic geometry but make it without bent wood.