oscillating shaft design 1

[Oespusaur]

I am working on creating an oscillating shaft system. Oscillation speeds are very low and it only moves +/-5 degrees, but rigidity of the system is crucial. This is a cantilevered system, and the load is approximately 150 mm from the closest bearing (150N - very light), and the overall system length is 500mm (cannot deflect more than .075mm at the end). Bearing spacing is 100-150 mm. Shaft size that the load is connected to is 20-25mm. I would like to use a plain bushing b/c of the oscillating motion, but there would be too much clearance. I am skeptical that ball bearings won't have the rigidity even with preload, but am worried that with line contact, I will see premature failure due to the oscillating motion. Under the described oscillating conditions, what is an appropriate bearing - or should I be seeking a special lubrication to prevent fretting/premature failure for a needle, tapered or cylindrical product?

 

[diamondjim]

Most bearings are designed for
complete rotation kind of ensuring
grease will be carried from the
non loaded to the loaded zone.
For the small oscillation of plus
and minus 5 degrees rotation, getting
grease to the loaded zone will be
your greatest problem. Some kind
of preload would help to ensure non
fretting. I do not know if you can
design some type of ratchet device
that would allow or ensure that one
of the races continually turns
thru 360 degrees. Or possibly you
can design a grease port or groove
to get the grease to the loaded zone.

 

[Hippo41]

Try using a full complement needle roller bearing like a NADELLA drawn cup unit.

The small diameter needles used in these are suited to osciallatory motion.

Lester Milton
Telford, Shropshire, UK