Reacting high torque in a tight area, box-end wrench max torque 1

[bc1080]

We have a through-bolt joint where there is very limited access to one side of the interface. We are planning to torque from the open side using either a torque multiplier or a calibrated electronic impact driver. The other side (restricted area) is a 12-pt nut with 1.5" flat-to-flat, and the only thing we have found that will fit over/around the nut is a box end wrench. They will probably have to brace the wrench against the side of the structure or index it against something to keep it from rotating during tightening. However, I am concerned about the ability of the wrench to withstand the 1000 ft-lbs we are applying with 1-inch drive tooling on the torquing side. I have not seen any limitations or documentation on torque after researching several wrenches. Most people seem to have a "use it till it breaks" approach. A common sense basis tells me the wrench is probably strong enough for what you would expect a human operator to be able to apply to said wrench, plus some safety factor to account for abuse such as a cheater bar. So if the wrench is 22" long, and if we can assume a human can apply 200lbs of force we only get 367 ft-lbs (times said safety factor, so maybe ~800 ft-lbs?), which is still a bit under 1000. Wasn't sure if there is more to go on or if there were any experiences with using a hand wrench for high torques.

The only crow's foot type wrenches I can find are flare nut type (due to the 12pt nut), and they are 1/2" drive which I do not believe would withstand anywhere near that much torque. I can't recall seeing much else tooling that might help here.

 

[MintJulep]

Once the joints starts to get tight the wrench is not reacting the full torque applied on the bolt.

Much (most) will be reacted by friction of the nut against whatever it is tightening to.

 

[bc1080]

That's a great point! I forget about that reality sometimes because we are typically asked to "ignore the effects of friction" for reasons of conservatism in analysis. It's probably actually pretty complex to try to estimate that torque relationship with the backing tool.

 

[tbuelna]

A 1.5" across-the-flats 12pt, 3/4" drive impact socket has a torque capacity of 18,000 in-lbs according to ANSI/ASME B107.2. The socket OD is 2.28".

A 1.5" across-the-flats 12pt, 1/2" drive impact socket has a torque capacity of 5,000 in-lbs according to ANSI/ASME B107.2. The socket OD is 2.12".

The torque capacity of a similar size box end wrench would likely be a bit less than a socket.

 

[racookpe1978]

An open-end wrench .. would have a much less torque capacity than any full-wrapped (circular) wrench design.

 

[SnTMan]

How about a Hammer Wrench?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[dik]

Shouldn't be using 12pt... 6pt for high torque.

Dik

 

[Tmoose]

Hi dik,

you said "Shouldn't be using 12pt... 6pt for high torque."

But the OP said " The other side (restricted area) is a 12-pt nut"

regards,

Dan T

 

[dvd]

Enerpac makes and rents some nice and compact bolting tools.

 

[MikeHalloran]

OR you could use Superbolts and ordinary torque wrenches.


Mike Halloran
Pembroke Pines, FL, USA

 

[bc1080]

Thanks for responses everyone! Wanted to follow up with some results from this during the initial test operations.

We are using the 6-pt on the open side we are torquing from, but we did have to use a 12-pt on the nut due to requiring a smaller tool/socket there (space restricted side).
We were using a hydraulic wrench very similar to the above to apply torque, and tried several tools before they were able to get 100% torque. The "tines" on the open-ended wrenches were "spreading" under the torque load and none of the closed end wrenches would fit around the nut. Ended up having to have a special wrench laser cut out of plate, basically a closed end wrench but with a "thin spot" in the area where it would be close to the wall behind the nut. After we finished torquing this tool was starting to plastically deform in the thin spot (probably would have be fine if we used something stronger than carbon steel.)

With all the trouble we experienced, my manager is allowing me to implement the "captive nut" concept I had designed initially and was shot down due to cost.