Picking the right radius for the Vee jewel bearing

V-jewel and cup bearing work best with minimum contact between the pivot (shaft end) and jewel.The design rule-of thumb is that bearin radius should be about three times pivot radius.

If the radius ratio is less than three,friction increases and movement becomes uneven.Too high a ratio- that is,a point-like pivot-results in excessive sensitivitiy,poor damping and repeatablitiy,and susceptibility to damage in handling.

Material selection is usually based on load,operating confitions.and cost.Sapphire is used when the assembly is solidly mounted and movement weight exceeds 0.2 g.Glass V-jewels have lower friction and cost,and are recommended when the load is less than 0.2g.Bearing diameters typically range from 0.04 to 0.125 in.A 40g load on a 0.05-mm radius produces a stress of 1,237 kg/mm2.But increasing the radius to 0.8mm reduce3s stress to 131 kg/mm2.