Questions regarding mounting of small Rod-End bearing

[John2004]

Hi Everyone,

I need to mount a small rod-end bearing as accurately as possible. The rod-end has a male stud, externally threaded. The rod end is part # POSB4 from IKO. The 1/4-28 threads are Class 3A.

I want to thread or press the male stud into the end of a round steel 1/2" diameter shaft (bearing shafting, probably 303 stainless, or perhaps case hardened steel)until the rod end housing OD bottoms-out on the end of the shaft. The shaft is adjustable up & down and is supported by a hardened jig bore bushing pressed into a 7075-T7 aluminum support base.

The bearing loads are radial to the rod-end bearing ball or race, but perpendicular to the rod-end mounting stud. There is no thrust loading on the rod end bearing ball / race.

I want the rod end bearing ball rotation axis (center of ball ID) to be on center with the center of the round adjustable shafting. There is .0012" maximum radial clearance between the ball OD and the race, but that is negligible.

Would I be better off threading the male rod-end stud into the end of the round shafting, or would I be better off pressing the rod end stud into the end of the round shafting ? I think the OD of a 1/4-28 class 3A thread OD has an overall tolerance range of .0065", which would be a heavy press. Even if I get it pressed in, it would probably distort the shaft OD to a point where it would not slide through the jig bore bushing.

Does anyone have any idea as to what type of positional accuracy tolerance range I might expect for the location of the bearing rotation axis, relative to the center of the adjustable round shafting ? I guess it depends on the tolerance of the part and how concentric the class 3A threads are (along with how accurate my tap is of course). I don't have any standards for rod-ends but I'm awaiting some feedback from IKO.

Any feedback, suggestions, or experiences would be appreciated.

Thanks
John

 

[unclesyd]

As you have a means to change out the rod end bearing I don't believe another screw connection isn't needed though if you have the precision nothing prohibits it.

I would go for a light press fit depending on the precision of the shaft and depth of the hole.

Can you comeback with a few more dimensions like the depth of the hole to be used and the precision of the rod?

If you use SS can you use a PH grade like 17/4?

 

[byrdj]

I hope I am visioning our discription correctly.

a method to ensure a threaded piece is centered to the end of the rod is to have a fitted collar (OD larger than the threads) that would engage with the last few threads. the threaded shafting would be chucked up and the size to size counter bore for the collar cut.

I don't think there was sufficient material between the ball and the threads. however if there is, make a jig to hold the inner ball to the outer race/stud, chuck the jig and cut some of the outer race to make the collar at the end of the stud.

you could put an oversized thread collar on and force it up to the ball and lock it. then chuck up on the threaded end, center the lathe jaws taking runout on the ball inners hole and faces, then cut the collar to size. Pretty involved process, but it should allow the alignment of less than 0.001 TIR.

 

[MikeHalloran]

You are stressing the ball end shank in bending. They're not designed for that, so I hope your loads are small.

Consider an alternative: Buy the rod end ball/socket only (I think you can get them that way), and press and stake it into a custom eyebolt- like piece with the 1/2" shank you need.




Mike Halloran
Pembroke Pines, FL, USA

 

[John2004]

Hi everyone,

Thanks for your replies.

>Can you comeback with a few more dimensions like the depth >of the hole to be used and the precision of the rod?

I was going to use a thread depth of at least 1.5 X the major diameter of the 1/4-28 thread. The rod the shank is threaded into would be ground shafting having an OD within .0002" & I would try have the rod going through a 1" long hardened drill jig bushing.

>If you use SS can you use a PH grade like 17/4?

That's no problem, I was trying to find stock shafting to use & I did not see that grade in my catalogs. The stock non-hardened stuff I found seems to be held at a little better OD tolerance than the case hardened stuff I found, otherwise, I would go with a case hardened shaft.

>You are stressing the ball end shank in bending. They're >not designed for that, so I hope your loads are small.

It is true that the shank is stressed in bending, but the entire shank will be surrounded by the material of the shaft it's threaded or pressed into (I want to press or thread the shank into the shaft until the ball housing OD bottoms out on the shaft end). The maximum load will be 148 pounds.

I may just do what Mike suggested as it would be more accurate, I just thought that since the rod end comes with a shank and housing, it would be easier to use it as opposed to making a custom part. Due to space constraints, I may have to use a .75" OD shaft to surround the spherical bearing, and then step down the OD where it enters the drill jig bushing.

Thanks again guys,
John