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rickmellor

Well Known Member
I feel like a total dork for this one. I was doing final assembly on the aileron bell crank in my 7A QB wing and I managed to twist the spar attach bolt off in the hole. It turns out that my fancy new inch pounds torque wrench doesn't work. :mad: I had it set to 20 inch lbs and I snapped the bolt off without even thinking about it (blindly trusting the tool). Now I've gotta figure out how to recover without destroying the platenut. The leading edge skin is on so I can't reach it to replace it.

Do you guys have any tips for this? I've got a tap set on the way from Avery but I've never done this before and this is a bad place to be learning.

-Rick
RV7A QB (emp done, working on the wings)
 
broken bolt

I hope you get some better answers, but here's what I'd do. Drill a small hole in the center of the bolt, and get after it with an ez-out.

Avery sells them, and I'll bet you can get them at your local hardware store.

http://www.averytools.com/p-427-alden-x-out-damaged-screw-remover.aspx

427.jpg
 
If I understand you correctly, you were installing the aileron bellcrank bracket in the wing, and broke one of the attach bolts. If so, the broken bolt is threaded into a nut plate that is riveted to the tie-down bar, and the tie-down bar is bolted to the font side of the spar. With the fuel tank removed, you have easy access to the tie-down bar, so you can remove it and replace the nut palte.
 
Yes, this is exactly the problem. It doesn't look like the x-outs will work because the bolt head twisted off. However, I'm going to pick up a set of these and see if it'll work. They'll come in handy anyway, I'm sure.

I hadn't thought about getting at it with the tank off. I haven't done anything with the tank yet so it didn't even occur to me. Thanks for the suggestion, that'll work beautifully and I won't have to worry about the integrity of the fix.

-Rick
RV7A QB (emp done, working on the wings)
 
How many foot pounds?

Do you think you must have put on the bolt?....To snap the bolt you must have put several times the torque required on the bolt...Or are these bolts weak?

Not critisising, just wondering how weak the bolts are??

Frank
 
It's an AN3 bolt so it's not too large. However, I'm a pretty strong guy and I have no sense for what 20 inch pounds feels like. After this my feeling is that it's not too much ... probably not much more than 'snug'.

I'm going to contact CDI and see if they can repair the wrench (or tell me how I'm using it incorrectly). The pic below is the wrench that I'm using. $149 from Avery.

608.jpg
 
Rick:

Are you new to using a click torque wrench? If not, disregard, if so, you may have just missed the indication. It can be very subtle depending on the wrench. Some give an audible click but most just give a small "yield" as you are pulling on the wrench. Make sure you use a VERY smooth and SLOW pull on all torque wrenches so that you can "feel" the subtle give.

Jekyll
 
Yes, this is my first attempt with one. I was expecting something like a ratchet effect once the set torque level had been exceeded ... kind of like the torque setting on my drill.

This model wrench is supposed to make a click sound when you reach the proper level ... I didn't hear one. After the nut broke I wanted to find out what was up so I put an extension in the vise, set the wrench down to the lowest level and tried to turn it. The thing would have broken before it clicked.

On a good note, I called Avery and they said to just return it for a full credit. They've never had one fail before, but maybe that's just my luck. :rolleyes:
 
That wrench looks awfully big, are you sure it wasn't 20 ft-lbs you were applying :rolleyes: . What is the torque range of the wrench? For reliable accuracy, the value should fall between 25% and 90% of the wrenches maximum value.
 
rickmellor said:
Yes, this is my first attempt with one. I was expecting something like a ratchet effect once the set torque level had been exceeded ... kind of like the torque setting on my drill.

This model wrench is supposed to make a click sound when you reach the proper level ... I didn't hear one. After the nut broke I wanted to find out what was up so I put an extension in the vise, set the wrench down to the lowest level and tried to turn it. The thing would have broken before it clicked.

On a good note, I called Avery and they said to just return it for a full credit. They've never had one fail before, but maybe that's just my luck. :rolleyes:
Click to expand...
Rick,
If you've never used one of these wrenches before, the "click" at the lower torque settings can be barely audible and often is felt as much as heard.
The wrench does not have a clutch like your drill and if you continue to increase force after the torque setting is reached you can certainly break the fastener.
It might be best to set the wrench at a fairly high setting and try using it against a large fastener in your vise to get a feeling of the operation. The click will be more pronounced at the higher torques. Keep testing at progressively lower settings until you get used to what to expect when the setpoint is achieved.
Just remember, 20 in-lbs is only 2 lbs force on a 10 inch lever (2x 10).
That is not much.

-mike
 
Been there, done that, had to call Van's

Jekyll said:
Rick:

Are you new to using a click torque wrench? If not, disregard, if so, you may have just missed the indication. It can be very subtle depending on the wrench. Some give an audible click but most just give a small "yield" as you are pulling on the wrench. Make sure you use a VERY smooth and SLOW pull on all torque wrenches so that you can "feel" the subtle give.

Jekyll
Click to expand...


This is exactly what happened to me when I was torqueing some bolts on the HS. I was expecting a ratchet-like action when I reached the setting. I just kept going and twisted the head off. I drilled it out and went up to a AN4. Fortunately, mine was easy to access. Good luck!
 
The extractors shown above are more applicable to removing philips head screws that have damaged slots. The cutters dig into the slots and tend to extract the screw.... if the screw doesn't back out, then the cutter will remove the head, and a pair a vice grips can then remove the stub of the exposed screw.... :)

The extractor for broken bolts probably should be like this....

20643.JPG


Called Extractor, Screw, Spiral Flute, 5/32" - 7/32" by Snap-On

....and a mere $3.40 in the Snap-On web site.... I think Sears has them as well...

gil in Tucson
 
Sears has them, but the snap-on ones break off in the bolt less often, and let me tell you, you DON'T want that to happen, tool-steel is a bitch to drill.

Guessing that that is a 15-200inch pound wrench, which most likely puts your 20" pounds in the part of the wrench where the click is very subtile, if you have trouble torquing AN3's buy smaller 1/4 drive torque wrench, one that is a lower range (say .5-75 inch/lbs if you can find one)
 
This wrench is pretty small, about 10" long. It's a 20-150 inch lb, 1/4" wrench... it's actually pretty nice.

So, I swung by the hangar tonight to check out some of the suggestions. It turns out you guys were right on. At 20" there is no click at all ... just deflection of the handle. On this wrench I don't get any click until around 80". This is surprising to me because the instructions that come with the wrench only describe a 'click' sound as the indication. Kind of weird that this is the key indicator but it's nearly non-existent. Oh well.

What I need to do is just go slowly and pay attention to the handle deflection. Once the set torque level is passed the handle will deflect about 3/4" at the end. I can't rely on a click at all.

For grins, here's a shot that shows the amount of deflection in the wrench.

wrench.jpg


Thanks for all the suggestions guys! I now know exactly what went wrong and how to recover.
 
It's fixed now

I pulled the tank off today and got at the tiedown bar. Once I had that out I was able to just twist the bolt the rest of the way through with a pair of vicegrips. After that I crimped the nutplates a bit to get them snug again and put it all back together ... using new AN3-6's for the brackets. It's good as new.

All in all, I'm kind of glad that this happened. I don't think I would have removed the tank otherwise, and now I know what that's all about. I think every quickbuilder should remove their tanks just to see how everything fits together. :)
 
Grainger sells this dial type torque wrench by Proto, a division of Stanley tools. The gauge to me is more reliable then listening or feeling for a "click".

 
A torque wrench made for bicyles works great. They are small, light weight and help you calibrate the feel for when you cannot get a torque wrench on the nut. Be careful pinching the nutplate as it will increase your running torque. For those just starting out, 20 inch-pounds is a 1-2 pound pull on a big torque wrench, a 3-4 pound pull on a 1/4 ratchet.
 
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Most people are startled at how little torque an AN3 plastic stop nut takes. 20 to 25 in-lbs is probably about 1/3 or so what most people would put on that size bolt if simply tightening it by feel.
 
Most people are startled at how little torque an AN3 plastic stop nut takes
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I agree. After learning how the torque wrench works I'm very surprised at how little torque is required for an AN3. This is one of those places where you have to trust the numbers.

The gauge to me is more reliable then listening or feeling for a "click"
Click to expand...
I'm more comfortable with the 'click' type now (although, the guage type seemed very appealing to me when I was having difficulties). And in some cases, I don't now how you could even read the guage. I'm thinking about when I have to set the torque on the fuel tanks. Some of those bolts are out of sight and I don't know if reading a guage would be possible. I think you'd want a tool that works on 'feel' in those types of situations.
 
AN3 torquing

Before I did any torquing of bolt and nut assemblies, I made up several dummy assemblies using scrap aluminum pieces. I torqued 4 or 5 bolt and nut assemblies to failure. The AN3's all failed by breaking the bolt and all larger sizes stripped the nuts. So AN3"s must be carefully torqued. You can check the "feel" of your snap action torque wrench by gripping the socket in a vise and the slowly applying force to the handle to feel the release action. Also it is important to center your hand on the handle when applying the torque for accuracy. Some torque wrenches have pivoting handles and you must have the handle "free floating" when torquing. I used the lower side of the torque range for AN3 fasteners just to be safe. Also all specified torque values are for "dry" assemblies (no lubrication). Wasting a few fasteners on test samples is well worth while and rather inexpensive. You will gain confidence in your workmanship! Norman Donaldson N214JD RV6 almost ready for final inspection.
 
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crimped nutplates

rickmellor said:
.... After that I crimped the nutplates a bit to get them snug again and put it all back together....

So why are nutplates crimped when many bolts use back nuts?
(just wundering).
Click to expand...
 
Nutplate needs replacing

rickmellor said:
I pulled the tank off today and got at the tiedown bar. Once I had that out I was able to just twist the bolt the rest of the way through with a pair of vicegrips. After that I crimped the nutplates a bit to get them snug again and put it all back together ... using new AN3-6's for the brackets. It's good as new.

All in all, I'm kind of glad that this happened. I don't think I would have removed the tank otherwise, and now I know what that's all about. I think every quickbuilder should remove their tanks just to see how everything fits together. :)
Click to expand...


I would strongly recommend that you remove the tank again and also replace the relevant nutplate. The stress on the first 3 engaged threads of a nutplate account for approximately 70% of the total engaged load. Therefore if you have overtorqued the bolt to the point of actually causing it to exceed it's Ultimate Tensile value (snapped it) then it is highly likely that the nutplate threads will have exceeded their Yield value. This could result in a sudden and unfortunate failure of the nutplate at any future time.

The nut holding the bolt that holds the aileron bellcrank is not something that you want failing in flight....high probability of complete loss of control.
 
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