NOTHING 11" in diameter is going to be inexpensive - those are essentially custom made bearings.
Generally, slewing ring bearings are custom made bearings and pricey.
4 point contact bearings are often LBNS - listed but not stocked. See prior sentence
Some bearing mfrs applications engineering depts can give you design assistance with moment stiffness but it can be hard to get thru to someone who knows what and how to do.
A/C's get pricey, especially in 50mm sizes due to the economies of scale involved.
A simple deep groove ball bearing can serve as a slewing ring bearing. However, if you apply a moment to it, stiffness is pretty much non-existant.
There is a book written by Harris (I believe) that goes into the mathematics of calc'ing pretty much all the stuff you discuss about bearings.
Keep this simple axiom in mind - you need a heavy preload to make a bearing stiff. A high net contact angle (60 deg for example in a ball screw bearing) with a bunch of preload will give the most axial stiffness. Add to this that moment stiffness is further enhanced by an INCREASE of the ball pitch and a ball bearing will roll easier than a tapered roller.
Simple case of packaging, economics and geometry.  |