I plan on trying to make a live center sometime this winter. I was going to use three angular contact bearings 7204 with a needle bearing on the end.
Do i want three single row or two double and one single?
Back-to-back I think is the setup. Is a double row also called a duplex?
Are single row made to be mounted as pairs or three?
Explain the factory preload.
Are all angular contact bearing preloads set?
Consider this to symbolize a center and one angular-contact bearing, with the center bearing on
the inner race and the outer race held stationary: " < ) "
As I understand it, identical bearings stacked back-to-back "< ( )" (or is it face-to-face?)
will take on the factory preload (the inner races being optimally resistant to both directions of thrust).
Preload just means that the 'slack' in the bearings is taken out (it takes some pressure on the
BBs to put their contact track in the correct part of the bearing race, and that force is the preload).
The preload then determines the centering accuracy of the bearing when it is not under thrust load
from the workpiece. The leftmost takes on extra load (thrust) only when you PULL on the center.
For LOTS of thrust, the addition of a third bearing in the correct orientation "< ( ) )" will share the load
in its resists-thrust direction. The bearings, to share, must be identical and in contact on
the outer races (i.e. not just slip-fit, but pressed, glued, or tightly clamped in a housing) as
well as on the inner races.
A double-row bearing is a "( )" or ") (" pair that cannot fail to have the races in the
factory-set preload. Adding a third race to the double-row means using a non-identical
thrust bearing, so maybe you don't want to do that. Two double-row would be good.
Non-angular-contact ball bearings (6200 seris) are accurate regardless of load, and can be put into the mix
just about anywhere (they have matched race lengths, so thrust just goes through to the next bearing
in line). Matched spacer rings (inner-race and outer-race with same length) can be tossed
in without changing the preload.
Needle bearings don't have races that match diameters with a stack; those confuse me.