Turnbuckle Initial Installation: AC 43.13 confusing

[haribole]

I was trying to interpret AC 43.13-1B, section 7-166. It states:

"When installing cable system turnbuckles, it is necessary to screw both threaded terminals into the turnbuckle barrel an equal amount. It is essential that turnbuckle terminals be screwed into the barrel so that not more than three threads on the terminal are exposed. (See figure 7-23A.) On initial installation, the turnbuckle terminals should not be screwed inside the turnbuckle barrel more than four threads. (See figure 7-23B.)"

This is confusing to me. When a turnbuckle is turned to tighten the cable, the number of threads exposed decreases as the cable end goes into the turnbuckle body. The circular states that initially there should not be more than threads "inside" the turnbuckle and finally not more than three threads exposed. Not sure how the threads will start exposing after being tightened.

How have others placed their turnbuckles initially?

Thanks
Hari

[jaredyates]

Hello Hari, it is great to see that you are getting so much done on your project! I agree that the wording is not very good. The way I interpret it, and please don't consider me to be any kind of authority, is that the four threads they are talking about are the female threads. So they are saying make sure your initial setting is between three male threads exposed and four female threads exposed. As you tighten the turnbuckle to a point where the male threads have passed inside of the end of the barrel, further tightening will increase the number of exposed female threads. Does my description make sense?

[haribole]

Thanks Jared. Sorry, but this is still not clear, feeling dense

I checked a few other FAA and Vans publications where it states that after tensioning there should not be more than three threads exposed. This makes sense, since if there were more threads exposed there may not be enough engagement.

Ah!! I think I got it now: It is like a eureka moment!

The second part just states that in the initial position the terminals should not be screwed in more than four threads. I can start with a good number of threads exposed, ( more than four threads screwed in) and tighten the turnbuckle such that in the final position not more than three threads are exposed. Now, what this good number has to be a trial and error I guess.

Yes Jared, things are moving along and the bearhawk is growing on me! Thoroughly enjoying the build process.

Thanks
Hari

[Craig C.]

You are close Hari... The initial setup should be that no more than three threads on the cable end are to be exposed when you start to tension it. Final tension on the cable should be where no more than the four end threads of the barrel are exposed. Remember the terminal shank is reduced after the threaded portion, and when screwed deep enough into the barrel, the outer barrel threads will no longer be engaged I don't have a barrel and fitting here to check, but that is something like 7 turns when tensioning. If you go much deeper than the four threads, then the terminal may not have full thread engagement with the barrel. You also run the risk of bottoming the two terminals into each other.

[haribole]

Yes Craig, this is the most logical explanation, but clearly the way this is described in AC 43.13 is exactly opposite.