Size, the taper angles are the same but the diameter is larger: see http://www.parlec.com/pages/bt_taper_specifications
Just from reading what people type on here I can figure out that a 50 taper spindle is more suited to do heavy cutting. I just wanna know why. What are the physical differences between a 50 and 40 taper spindle? Is a 50 taper spindle just more robust and rigid then a 40 taper spindle? Also are there any other advantages besides heavy cutting that a 50 has over a 40 taper spindle. Sorry if my question does not make complete 100% sense. The machine shop I use to work at taught me everything about programming and set-up so I never needed to know about the specifications of machines.
So that means that tool holders would need to be bigger for a 50 taper then a 40 taper. Ahh I see. So the fact that its larger in diameter makes it better for heavy cutting?
Hmm, seems like it, because of more surface area.
spindle RPMs are (usually) higher with smaller tapers
50 taper machines usually (almost always) have heavier, larger spindles and bearings. Also, slower spindle speeds. This more robust combination results in heavier cutting capability and the ability to employ larger tools. eg. larger dia. face mills.