Hi everyone,

Thanks for your replies,

Carl Mciver wrote:
How possible is it for you to provide a light duty thrust bearing where the
housing nears the support? It could be roller or brass (better roller, I
suspect, because of less wear and slop,) but either way it will pass some of
the load around the pin, letting you focus more on the shear load rather
than the cantilevered beam loading (you have to have a tight fit or that
will be a part of it, though.)

John2005:
I was thinking along the lines of using a thrust washer as well. A
needle bearing thrust washer would be ideal, but it's really kind of
expensive for a product like this. Brass or steel would be OK if it can
be quiet over the life of the product, and wear OK with no additional
lubrication beyond lubing at assembly. I was thinking of using a
plastic thrust washer like Delrin or PEEK.

I have a couple of choices with regards to how I mount the housing. The
dowel / shaft is a "pull dowel" with a tapped end. I was going to hold
the housing on with a screw going into the end of the dowel. I could
put a thrust washer between the housing and the cantilever support, and
put another thrust washer between the screw head and the loaded end of
the housing. I would put a little dab of loc-tite on the end of the
screw threads, then just snug the screw down to take up any axial play
in the housing, but without any significant drag. When the loc-tite
dries, the screw would never back out due to the oscillation of the
housing. I had also considered using some "long-lok" screws or some
screws with the nylon patches in conjunction with the loc-tite, so I
would not have to keep the parts setting completely still until the
loc-tite dries, i.e., the nylon patch or long-lok screw keeps the screw
from backing out while the parts are being handled during assembly, and
then when the loc-tite dries, the screw should never back out during
use. Otherwise, I could just wait for the loc-tite to dry.

It may be possible that a long-lok screw or a screw with a nylon patch
on the threads would work by itself without loc-tite, I would have to
test to see. I would not think there would be much force or friction on
the screw head to cause it to loosen and back out.

I think the thrust washer would stiffen everything up, "until" it
wears, and then when you get play, you are right back at square one. If
I can find a material that will be quiet and work well in a situation
where re-lubrication is not possible after assembly, it may go a long
way to making everything stronger, because then I would have the
stiffness of the shaft, and also the .905" OD housing, which I would
think would hold a very large force, since the overhang is fairly
short. It's just a matter of getting a thrust washer that will be quiet
and last, and be cost effective.

I used my beam program to model a torque moment between the two
bearings, in the middle of the span, and the stresses and deflections
were much less than with vertical forces. If the forces of each bearing
are purely vertical, both pushing down, then the 3/8" OD shaft deflects
about .001" further than the 7/16" OD shaft, but with slightly less
bending stress. However, if the forces are a pure torque moment, with
the rotation axis in the middle of the two bearings, then the 7/16"
dowel deflects .002" less than the 3/8" dowel, and with about 10 KSI
less stress.

Probably testing is the only way to find out, I don't think the bearing
load will be a pure torque moment, or a pure vertical force, and I am
not sure how to divide the load up between vertical and torque forces.

Thanks again,
John