ppytprs wrote:Hard to spring convincingly!
The trick here is to use rather soft and long springs that are highly commpressed when installed. This minimises the difference in pressure between the top and bottom of the key travel and, in my view, gives the best feel. Personally, I think this is better than weighting the backs of the keys which achieves the same aim to some extent but also increases the inertia which makes them heavier for fast depressions and can compromise the maximum repetition rate.
I make my own springs using piano wire and a lathe; this allows for quite a lot of experimentation but assumes you have lathe to start with. It would be an expensive route otherwise.
Given the lengths of the keys each side of the balance rail, and the desired pressure it should be possible to calculate the required rate and uncompressed length of suitable springs.
Nick