Mad About Wool,
spinning silk on the book charkha is for those with iron will. the book charkha has a very high spin ratio (1:65 which is why it's so great for short fibers like cotton, cashmere, angora etc), so unless the bombyx is blended with cotton,cashmere or angora, the possibility of going nuts while spinning such a long fiber on the book charkha is high.
However, spinning silk on something like the Attache charkha (a larger version of the book charkha) would be easier since it doesn't have such a high spin ratio.
I think bombyx/mulberry are best spun on a regular wheel with the lowest ratio on it.
hope that helps