Hi everyone,

Does anyone know if there are any standards that apply to the accuracy
of spherical rod-end bearings ? I would be using a rod end such as the
6072K21 from www.mcmaster.com or the POSB4 from http://www.ikont.com/.

The IKO bearings have a class 3A thread on the male threaded mounting
shank. I mainly need to know how accurate the rotation axis of the ID
of the rod end ball or inner ring is, compared to the center of the
male threaded mounting shank. How concentric the threads are & the
tolerance on the OD of the shank threads is also a consideration. I've
sent emails off to three rod end companies but have not received a
reply as of yet.

I have a small, thin rectangular plate, that will pivot or oscillate
on two rod end bearings located at each end along the front edge of
the plate. The male threaded rod end bearings will be screwed into the
ends of two 1/2" OD round steel posts (bearing shafting) that are
adjustable up and down inside of a hardened drill jig bushing that's
pressed into a 7075-T7 aluminum base. I want to thread the rod-ends
into the round posts all the way until the rod-end housing OD bottom's
out on the end of the shafting. Since only one post can be adjusted at
a time, (the adjustment point cannot be in the middle of the posts) a
spherical bearing is needed to allow for adjustment, otherwise, the
bearings & shafting would bind or bend during adjustment.

After adjustment, there is no significant mis-alignment of the
bearings. My loads will be radial to the rod end bearing or ball,
(there are no axial loads) but perpendicular or at a right angle to
the threaded mounting stud. The maximum load on each bearing will be
148 pounds. The oscillating speeds are very slow and all forces can be
considered static. I want very low friction at the bearings so I'm
going to press a drawn cup needle roller bearing into the ID of the
rod-end ball. The bearing shaft will rotate inside of the needle
roller since this will be the low friction point, and the rod-end ball
should not rotate in it's race as the rectangular plate oscillates.
The rod end ball will only provide for periodic adjustment of the
mechanism, & shaft rotation should take place inside of the needle
roller. I know they make ball bearing spherical rod ends, but the
cheapest I found was about $80.00 bucks each, so it's much cheaper for
me to press in a drawn cup needle roller into the ID of a standard rod
end , especially since I have no axial loads to worry about.

If I thread the male mounting stud of the rod-end into the end of the
round steel shafting / adjustment post, what type of positional
accuracy and tolerance would seem reasonable to achieve relative to
the center of the post ? I would want the bearing rotation axis to be
in the center of the round steel post. The shafting OD is ground to
within .0002", so it's mainly just a matter of how accurate the rod
end is and how accurate my tap is.

I mainly need accuracy along the Y axis, as the X axis is more
forgiving and the Z axis does not matter since it's adjustable along
the Z axis.

I would appreciate any feedback, advice or suggestions.

Thanks
John

On Aug 7, 11:26 am, John2005 wrote:

... I mainly need to know how accurate the rotation axis of the ID
of the rod end ball or inner ring is, compared to the center of the
male threaded mounting shank.

If its not detailed on the manufacturers drawing then its not
guaranteed. Rod ends are usually used for transmitting forces and not
used for locational accuracy. I would be surprised if the bore
aligned with the mounting any better than 0.01 inches.

... The maximum load on each bearing will be
148 pounds. The oscillating speeds are very slow and all forces can be
considered static. I want very low friction at the bearings so I'm
going to press a drawn cup needle roller bearing into the ID of the
rod-end ball.

The needle bearings are overkill. Teflon or UHMWPE inserts would be
just fine and would probably be lower friction.



If I thread the male mounting stud of the rod-end into the end of the
round steel shafting / adjustment post, what type of positional
accuracy and tolerance would seem reasonable to achieve relative to
the center of the post ?

That's what aound here they call making a silk purse out of a sows
ear. Though I think a sows ear purse would be pretty cool. You
could make them up and sell them at the hippy fairs. Call 'em
'organic'. Give 'em cute names like Little Bacon, or Miss Piggy.


starbolin

Thanks for your reply Starbolin,

I think I'm just going to use a precision spherical bearing (bearing
only, not a rod end with a mounting stud) and press it into a custom
made adjustable post, that way I can control the positional accuracy
and not rely on the tolerance of a stock part. I doubt the rod-ends
have a specified tolerance for the location of the inner ring ID
relative to the mounting stud ID, and even if they do, I agree with
you that it's probably no better than .01" max.

John