What would be a bigger load, the load of driving the belt or the radial load of a 7mm doc/1mm woc cut? The torque at 12k rpm is enough for the cut itself, wouldn't it be enough when underdriven via a set of pulleys?

It is quickly becoming apparent that the most demanding aspect of the design is the part I overlooked the most, the bearing arrangement. I spent hours and hours reading up on it and it's still kind of a mystery to me. I've narrowed it down to two possible designs.

The one is a couple of back-to-back universally matchable angular contact bearings at the bottom and a common deep grove up top. The inner races of the bottom set will be held together by a KM nut (top portion of the 35mm dia part of the R8 shaft will need to be threaded), and the outer races by a flange on the bottom of the housing, which will incorporate a radial oil seal as well. How much will the bearings will be preloaded and how the preload can be measured is still unknown to me.

The other design is sort of a clone of the Tormach spinle, ie a couple of angular contact bearings at each end of the shaft. The tormach design incorporates preload washers at each end for the bearings, but weather they are used to have the best possible contact on the inner races or as a seal (or indeed anything else) is unclear to me. Again, how much the bearings need to be preloaded is a bit of a mystery to me.

If anyone has any ideas, please share. I'll try to post a drawing of each design soon.