Last week I was regrinding my spindle taper and reduced runout by 3-4x now it is 0.01-0.02 depending where I measure at the distance of 100mm runout is 0.01 and for longer toolholders it increases, for short ones it reduces. there was tools that had almost 0 runout unmeasurable by my dial indicator
I spend 2 weeks on spindle first I completed ER20 grinding spindle I started to build last year and leaved it unfinished, i will post pictures later.
here is video I compiled of 10 small videos. my goal was to improve surface finish cutting aluminum and now it is much much better.