Oversized Elevator Horn Hole

[clutch22]

The other day I was working on drilling out my elevator horns on page 11-3 of the plans. The plans call for a 3/16" dia. hole that will eventually be for the AN3 bolt. Long story short, I ended up accidentally with a #10(.193) bit instead of #12(.1875) bit. I only drilled through one horn before I realized this. So now I have a perfectly round hole that is slightly oversized about .0055". It's enough that I can tell the slop compared to the bolt going through the rod end bearing.

I saw a few others before me had welded their holes shut and redrilled when a problem similar to this had occurred. I went ahead and asked Van's for their advice. The reply I got was to TIG weld it shut, because if I stepped it up to an AN4 hole then I would have problems with having to step up the rod end bearing.
But what about this? I think I can get a rod end bearing for an AN4 bolt that has the same threads as the smaller blueprint bearing, and importantly is the same width between elevator horns. My edge margin would be decreased but I feel that it would be okay still due to the fact that it's a steel part.

On the Aircraft Spruce link below, click on "Specification Chart". I'm comparing the blueprint MD3616M bearing to my proposed MD4616M bearing.

http://www.aircraftspruce.com/catalog/appages/aurorabearings.php

 

[Jesse]

We've always welded them shut then redrilled. I don't like the idea of going oversized, but mainly for the sake of keeping it per plans on such a critical component. If you have all of the edge clearances required by the plans for the 3/16" on your 1/4" hole, that shouldn't be a problem

 

[Bill.Peyton]

Andrew,
I see you are part of the material review board at Cessna. What would you do if this was a work related issue? That's the question to ask of yourself. I would re-work the part by TIG welding it closed, and stick to the plans.... As Jesse stated, it's a critical component.

 

[DanH]

In my opinion, a perfectly reasonable substitution. One might even argue it is a desirable substitution.

 

[clutch22]

What would the edge distance be with the AN4 fastener?

I don't see a problem with your plan if:
- the edge distance is good
- there won't be any other geometric conflicts caused by the large bolt and rod end (the larger rod end seems to be a bit longer in some dimensions and also has *less* allowable ball rotation)

The minimum e/d between the two horns is measuring .35" which is slightly less than what I would normally accept at 1.5 e/d which would be .37". However, since these are steel parts, and each measuring approx. .070" thick, I feel that the lower e/d should be fine if drilled to a 1/4".
I cant think of any interfering geometric conflicts that would occur coming from the few specific areas on the bearing that are different. As far as the reduced allowable ball rotation goes, that should only be an issue of the bellcrank isn't aligned on center with the elevator horns. I haven't looked into that, but I'm assuming it definitely would be?...

I see you are part of the material review board at Cessna. What would you do if this was a work related issue? That's the question to ask of yourself. I would re-work the part by TIG welding it closed, and stick to the plans.... As Jesse stated, it's a critical component.

Welding the hole shut and re-drilling it is something that we wouldn't do. We would lose the quality control on the temper after heating it like that. It would most likely be dispositioned to remove and replace the whole horn assembly or to accept the larger hole.


Thanks to everybody so far for providing their input!