Quote Originally Posted by Robert Steinwandel View Post
I meant to ask about this much earlier, but would you mind explaining more about the spindle length issue? Im not sure I fully understand the different factors involved here
For this little lathe it may not be much of an issue, depending on how it is going to be used, how much power the Moter will have and the types of materials and cutters planned to be turned and used.
However the lathe makers of old had a general practice of placing the head stock bearings at a minimum distance of 1.5 times the diameter of the total swing, now some of this may have been due to the need for more space for the widths of the flat belt pulleys allowing for multiple speed changes, later being reserved for the transmission gears as in gearhead lathes. But a lot of it was to reduce the loading on the smaller bearing at the rear of the spindle and to help in controlling runout when turning or facing. This T reduce shaft flex due to the longer length many manufactures had spindles much thicker at one end not only because the bearing at the chuck end was larger since it sees more loading but since the forces were lower at the other end not as much material was required there,
Think of how the spindles on heavy duty truck and trailer axles are designed the outer bearing is smaller than the inner bearing because the loading is much less.
Very old heavy duty lathes had a split sleeve bearing at the big end of the spindle with a large flat thrust bearing sometimes made out of leaded bronze, and sometimes a caged ball bearing on the other end or just a smaller split sleeve bearing, Latter on the practice of utilizing tapered roller bearings on the spindles became the norm as they were easier to adjust by adding an amount of preloading the better lathes took this one step further and added a angular contact caged ball bearing between the larger tapered roller bearing and the spindle nose. Some lathe manufacturers did away with the tapered roller bearings altogether in lew of using multiple pairs of radial and angular contact bearings using an angular contact bearing facing the opposite direction at the rear of the spindle, this idea worked fine for drill presses but was very lacking in holding the spindle true as the bearings wore a little. Some car manufactures used ball bearings for their front wheel bearings that were not angular contact it proved to not be a good idea and abandoned the design. it wasn't until front wheel drive cars started becoming popular that ball bearings returned only now being angular contact.
So, since I am often accused of liking to type to summarize, when building a lathe or anything else for that matter look to the manufactures of old especially those who are still around after a 100 years and see how they have done it what they are still doing and in what way have they altered their designs to achieve their success .