RV-12 control column bearings too tight

[JimMac]

When I fabricated the control column bearing brackets in which the control column pivots, the bearings would not turn freely. I guess when I squeezed all those an470-4's around the bearing, the bearing got stressed some way. I put an AN3 bolt in it and could swivel it around but it was stiff. I (mistakenly, I think now) decided to go ahead and rivet the brackets onto the bulkhead, which has now been installed onto the seat ribs, thinking that it is the bolt that will be turning inside the bearing. But now I realize that the bolt will be jammed up tight against the bearing and it will be the bearing itself that will be turning - not the bolt inside the bearing. (I hope this isn't too confusing). Now my question: Is it VERY important that there is no binding in these bearings? If it is, then I should try to drill out all 16 LP4-3 rivets in each bracket where they are riveted to the seat-front bulkhead (if I can still reach them) and refabricate those bearing brackets.
I don't want to find out on the first flight that my stabilator control has a "stiff" spot. Has anyone else encountered this and are there any any suggestions???

 

[joedallas]

Bearings ?

Jim my control columns bearings also got a little tight when I installed the rivets , however they still can be tuned by my fingers so I think they will be OK.

Can you turn the Bearings by Hand

I just installed them on friday.


Put a long Bolt in the bearing and lift it up and down forward and back this should free up the bearing it worked on mine.

When I fabricated the control column bearing brackets in which the control column pivots, the bearings would not turn freely. I guess when I squeezed all those an470-4's around the bearing, the bearing got stressed some way. I put an AN3 bolt in it and could swivel it around but it was stiff. I (mistakenly, I think now) decided to go ahead and rivet the brackets onto the bulkhead, which has now been installed onto the seat ribs, thinking that it is the bolt that will be turning inside the bearing. But now I realize that the bolt will be jammed up tight against the bearing and it will be the bearing itself that will be turning - not the bolt inside the bearing. (I hope this isn't too confusing). Now my question: Is it VERY important that there is no binding in these bearings? If it is, then I should try to drill out all 16 LP4-3 rivets in each bracket where they are riveted to the seat-front bulkhead (if I can still reach them) and refabricate those bearing brackets.
I don't want to find out on the first flight that my stabilator control has a "stiff" spot. Has anyone else encountered this and are there any any suggestions???

 

[videobobk]

First, I don't think that it would be possible to get the bearings so tight that you couldn't over power them, but this is an area where smoothness is important. Also, if they are under stress, they are going to wear. Somewhere down the line, they will wear out, although that may be a long time. This is a case where it is better to fix a problem when you first notice it, rather than build around it. I would suggest biting the bullet and doing it right. Make sure everything fits without binding, and be sure you have deburred the mating surfaces. It doesn't take much here...

Also, in the answering post, painting (or priming, in this case) may be your only problem with stiffness. It is good practice to mask the bearings, or prime before assembly (a better option.)

Bob

 

[JimMac]

RV-12 Control Column bearings too tight

Joe,
Thanks for the response.
No, I don't think I can turn the bearings by hand. I think I'll have to order new bracket parts and remake them. I'll try to drill out the rivets to separate the brackets from the bulkhead and hope I can put them back in without detaching the bulkhead. Thankfully, they are all LP4-3 rivets which are a little easier to drill out cleanly than some of the others. Maybe I can take a dremel tool with a cutoff disc and cut the back of the rivet off first and then drill it out from the head side. Is there some technique I'm missing about how to sandwich bearings properly? Is the trick to squeeze the rivets around the bearing a little at a time going from rivet to rivet?

 

[joedallas]

Baring ?

Try to free them first

Put a long Bolt in the bearing and lift it up and down forward and back this should free up the bearing it worked on mine.

Joe,
Thanks for the response.
No, I don't think I can turn the bearings by hand. I think I'll have to order new bracket parts and remake them. I'll try to drill out the rivets to separate the brackets from the bulkhead and hope I can put them back in without detaching the bulkhead. Thankfully, they are all LP4-3 rivets which are a little easier to drill out cleanly than some of the others. Maybe I can take a dremel tool with a cutoff disc and cut the back of the rivet off first and then drill it out from the head side. Is there some technique I'm missing about how to sandwich bearings properly? Is the trick to squeeze the rivets around the bearing a little at a time going from rivet to rivet?

 

[joedallas]

Squeeze the rivet not the bearing

These are double flush rivets, when you squeeze the rivet use a small diameter flat die in both sides of your squeezer and don't let it hang over on the bearing side of the Rivet.
Squeeze the rivet not the bearing.

Also like bob said

Deburr the Bearing seat in the Brackets.

Joe,
Thanks for the response.
No, I don't think I can turn the bearings by hand. I think I'll have to order new bracket parts and remake them. I'll try to drill out the rivets to separate the brackets from the bulkhead and hope I can put them back in without detaching the bulkhead. Thankfully, they are all LP4-3 rivets which are a little easier to drill out cleanly than some of the others. Maybe I can take a dremel tool with a cutoff disc and cut the back of the rivet off first and then drill it out from the head side. Is there some technique I'm missing about how to sandwich bearings properly? Is the trick to squeeze the rivets around the bearing a little at a time going from rivet to rivet?

 

[Mich48041]

Page 21-10

In some of the early kits, the manufacturer had problems milling the bearing recess to the proper depth. When the parts were riveted together, the bearing was squashed because there was not enough room for it. When you get the new parts, use a micrometer or calipers to make sure that there is enough room for it.
Joe Gores

 

[JimMac]

Re:Control Column Bearings too tight

Thanks Joe and Mich for your inputs.
I Scotch-Bright'ed and primed the middle piece of aluminum so maybe that was my mistake. I might have made that piece just a tad thin so that the outside pieces of the sandwich pressed in too tight on the bearing housing. I have ordered new parts for these brackets and I will remake them.

One more question: If I run into this problem again with the new parts, is it permissible to not torque the nut down all the way and leave it just loose enough so that the bolt can turn in the bearing even if the bearing itself won't rotate? Will the lock nut stay on even if not torqued to 25 in-lbs?
Thanks,
Jim

 

[joedallas]

Free the Bearing

jim

I Scotch-Bright'ed and primed the middle piece of aluminum also
That is not the problem.
The bearing needs to be free rotating, rotating on the bolt is not a good idea
I think you over squeezed the rivets or the bearing recess was not deep enough of had a burr like joe Gores said

Or your counrersink was to deep and you squeezed the bearing not the rivet

Thanks Joe and Mich for your inputs.
I Scotch-Bright'ed and primed the middle piece of aluminum so maybe that was my mistake. I might have made that piece just a tad thin so that the outside pieces of the sandwich pressed in too tight on the bearing housing. I have ordered new parts for these brackets and I will remake them.

One more question: If I run into this problem again with the new parts, is it permissible to not torque the nut down all the way and leave it just loose enough so that the bolt can turn in the bearing even if the bearing itself won't rotate? Will the lock nut stay on even if not torqued to 25 in-lbs?
Thanks,
Jim

 

[Mich48041]

Any bolt subject to rotation should have a castle nut and cotter key. But like Joe Dallas said, rotating on a bolt is a bad idea. The parts will wear quicker compared to a free turning bearing.
Joe Gores