MRA, there's a Workshop Practice Series #27 book called Spindles by Harprit Sandhu that contains a lot of different spindle designs; various OD & length sizes & bearing type/configurations. (My opinion) on the plus side the book is good in that its orientated to the practical hobby machinist. You can pick a drawing, adapt it to your machine & build it from his dimensions. But aside from 'conversational enlightenment', pretty light on engineering details as to why you would select one configuration over another. Mostly I was looking for specific guidance on bearing play setup & adjustment which is probably where the magic happens, but probably also at the expense of bearing life/heat etc. I see commercial spindles with adjustment nuts and wavy washers, but I don't see similar assembly components in the book designs, so I'm not sure what to make of it. Maybe a different path to the desired end result, or? It almost looks like the machining effort is about the same for all the spindle designs in the book +/- intended shaft details like whether it has a taper socket end to match some tooling purpose. Unless you go with uber precision AC bearings, I figure the overall materials cost doesn't vary too much so may as well build the best design - whatever that is.
I'm still on the hunt for a compact spindle design suitable for light but precision grinding using big wheels. There's lots of pictures & videos on the net that show a shiny part. But like the polished potato analogy, that's not the same as hitting a dimension to X decimal places with appropriate finish. I do think there is merit in a standalone spindle driven by external motor because a) you gain independent control of runout vs an integrated motor repurposed from another tool b) it removes a big bulky motor from the working area.
The reason is that I've done my spindles earlier!
