torque wrenches with crows feet

[JackOfDiamonds]

I need to torque some HVAC lines and thought I could use crows-foot extensions on my torque wrench with a correction factor.

I found this Air Force spec online which says that no correction factor is needed:

https://www.robins.af.mil/Portals/59/documents/technicalorders/32B14-3-1-101.pdf

When a standard crowfoot attachment is used on a torque wrench, no torque correction is required. Torque to specified value or, if applicable, to center of specified range.

Should you

1--use crows foot at 90 degree angle and apply no correction facton
2--use crows foot straight, and apply a correction factor (which one)?
3--something else?

 

[SteveH-CO]

I would think that a crows-foot wrench (the typical type) incrementally makes the torque wrench longer (by maybe 5-10%) and thus the torque values should be decreased by that amount. I wouldn't lose a lot of sleep over correcting your values.

 

[vavet]

I'd think you'd need a small correction factor. It wouldn't be much, but it's not zero.

 

[Bigblue&Goldie]

I'd do 90 with no correction.

 

[BukitCase]

I'm with Bigblue on this - I would be a LOT more concerned with making sure whether your torque spec was for dry or lubed - if you lube the fastener and then use a "dry" spec, you will VERY likely be finding a way to remove a headless bolt (BTDT, got the T shirt) ... Steve

 

[Eli D]

From ac43-13.2b for torque on civilian non pressurized aircraft

 

[Eli D]

Also there’s an app for that
I think its torque adapter app

 

[InsanePyro]

That seems like a stretch to me but only because any crows foot I've ever used has had some slop to it. With that being said they sure weren't any name brand crows feet

 

[Rusted Nut]

Either choice #1 or #2, will work. #1 would be preferable if you can get the crows foot to work that way.

 

[Honch]

#1 is the simplest way, and commonly used.

 

[budget76]

at 90* no math required. if straight on math is required since you are lengthening the lever arm

LW = effective length wrench
LA = length adapter


this only works with beam wrenches, it does not translate to clickers and clickers do not have a way to calculate like this. for your application i doubt it matters, but in the jet engine mfg business we do not use clickers for various reasons, and this is one of them

 

[JackOfDiamonds]

It's interesting you make a distinction between click and beam in this way. I believe you, because even with my training in physics, this configuration is really a stumper for me. But I can't see the difference between click and beam because torque would seem to be torque...

In practice, for my 1/4" and 3/8" copper HVAC flare fittings, what I did is use the crows foot straight and torqued to the middle of the range, using my harbor freight clickers, with no correction factor. Then, since that seemed too loose for my instincts, I gave the fittings another slight tweak tighter with plain wrenches (forgive me for I have sinned) with no regrets because it was far from any kind of danger zone of cracking the fitting or anything.

I'm still glad I used the torque wrenches even though I ignored them because at least I'm confident now that they are tight enough. When I torqued the electrical connectors in my sub-panel, the situation was different because I ended up tightening those much tighter with the torque wrench than I would have done by hand.

 

[Rusted Nut]

at 90* no math required. if straight on math is required since you are lengthening the lever arm

LW = effective length wrench
LA = length adapter


this only works with beam wrenches, it does not translate to clickers and clickers do not have a way to calculate like this. for your application i doubt it matters, but in the jet engine mfg business we do not use clickers for various reasons, and this is one of them

I’m not doubting you, but can you explain why this wouk$ not apply to click type torque wrenches?

 

[Ike Carlson]

this only works with beam wrenches, it does not translate to clickers and clickers do not have a way to calculate like this. for your application i doubt it matters, but in the jet engine mfg business we do not use clickers for various reasons, and this is one of them

Please explain WHY it does not work with a click wrench. Torque is torque, and the wrench will click at the same time the beam says stop. We used both when replacing a head gasket this spring and it was interesting to see the torque climb with the beam wrench vs feeling the click from the other. Both stopped in the same place.

Torque wrench length doesn't matter because it is calibrated to indicate the correct value. You could have a 12" torque wrench and a 36" torque wrench and both would read the same or click at the same point because they are calibrated. The effort on the shorter wrench would be much higher, but it would still be accurate. The only thing that matters is the length of the crows foot and the angle from which it is being driven. 90° on a short model requires near zero correction, while any other angle will have varying degrees of correction. The actual angle for zero correction is a little less than 90°, but crows feet are usually indexed at 0, 90, 180, 270 degrees so we use 90° as the zero point.

Crows feet are normally very short, so correction is not a huge concern as it is usually within the margin of error.

 

[GoToGuy_Ron]

If your using any type of torque adapter and you are not correcting the applied torque value, your wrong. If that crows foot has 1 inch from drive center to center of crows foot your 24 inch torque wrench is now 25 inches. If you work in Aviation and don't do the math your wrong.
When was the last time you had your torque wrenches calibrated?
AC 43.13 is acceptable methods for repair service on Aircraft. All aircraft, not just pressurized jet.

 

[budget76]

I’m not doubting you, but can you explain why this wouk$ not apply to click type torque wrenches?

i don't have the packages handy, but companies such as Sturdivant Ridgemont have published documentation that state clicker style wrenches cannot be reliably used with torque adapters. It is something to do with the physics of the way the internals of the wrench react and changing the lever arm longer with an adapter does not reliably correlate 1:1 to the equation listed above like a beam does. if I re-find the document I'll scan it

At OEM jet engine manufacturing, we do not permit torque adapters to be used at any angle except straight on or 90* from the wrench handle. We ironically were shipped 6" extensions from snap on with the square drive offset 45* from the other end and had to discard them from the floor, to avoid them being used with torque adapters. We do not permit click style wrenches for use anywhere due to the extra care they require with relaxing the spring, 'stretching' it prior to use, etc.

we, for various reasons, hold ourselves to tighter requirements than the field and other sites do.


do I think it's overkill for myself in my shop? probably. Sounds like Ron's lived similar discussions in his past

 

[joe_padavano]

I'm more than a little amazed that this topic requires so much discussion. Applied torque is force times lever arm, period. Change the lever arm and you change the applied torque. You can either use a correction factor or use the adapter in an orientation that doesn't change the lever arm. And FYI, 90 degrees does NOT produce an equivalent lever arm, though for a very short crow's foot adapter it's probably close enough. Longer adapters create more of an error at 90 deg. As an example, if you have a 6" long adapter at 90 degrees to an 18" long torque wrench, you'll apply about 5% more torque than indicated. You'd have to angle the extension at less than 90 deg to achieve the same 18" lever arm.

 

[PCustoms]

I'd do 90 with no correction.

Old thread but post #4 was the answer.

Edit: completed the thread. There's some interesting "information" here. Some of you go read how wrenches are calibrated and what deviation is acceptable.

 

[budget76]

I'm more than a little amazed that this topic requires so much discussion. Applied torque is force times lever arm, period. Change the lever arm and you change the applied torque. You can either use a correction factor or use the adapter in an orientation that doesn't change the lever arm. And FYI, 90 degrees does NOT produce an equivalent lever arm, though for a very short crow's foot adapter it's probably close enough. Longer adapters create more of an error at 90 deg. As an example, if you have a 6" long adapter at 90 degrees to an 18" long torque wrench, you'll apply about 5% more torque than indicated. You'd have to angle the extension at less than 90 deg to achieve the same 18" lever arm.

the last statement is not how it is treated on OEM jet engines. 90* is treated as the same as no adapter. I have never seen otherwise in any torque wrench manufacturing specification/training package.

that doesn't mean I don't agree with your thinking that your moment arm gets wonky if the adapter length hits some ratio of the wrench length



end of the day. for a home mechanic not trying to hold torques to <2% accuracy, do the math with whatever wrench you have on hand and you'll be fine

 

[joe_padavano]

the last statement is not how it is treated on OEM jet engines. 90* is treated as the same as no adapter. I have never seen otherwise in any torque wrench manufacturing specification/training package.

Like I said, if the adapter (crows foot) is short enough, the inaccuracy is small enough to be negligible. Add to this that it's a lot easier to turn the head to 90 deg than some oddball angle. Practicality frequently is more important than 100% accuracy.

 

[PCustoms]

Like I said, if the adapter (crows foot) is short enough, the inaccuracy is small enough to be negligible. Add to this that it's a lot easier to turn the head to 90 deg than some oddball angle. Practicality frequently is more important than 100% accuracy.

I highlighted the magic part.

 

[Firebrick43]

the last statement is not how it is treated on OEM jet engines. 90* is treated as the same as no adapter. I have never seen otherwise in any torque wrench manufacturing specification/training package.

that doesn't mean I don't agree with your thinking that your moment arm gets wonky if the adapter length hits some ratio of the wrench length



end of the day. for a home mechanic not trying to hold torques to <2% accuracy, do the math with whatever wrench you have on hand and you'll be fine

The US navy, the second largest operator of aircraft in the world allows click type wrenches with offset extensions, no correction at 90.

It appears the AF does as well as long as one doesn’t try to use the ratchet head in reverse or calibrated it both ways.

Deflection torque wrench’s are more accurate in the lab but not in the field. One can not get to a point where they can see the gauge dead on when working in the field. Just because you can on an assembly line or test cell it irrelevant to the line mechanic.

There are many jobs that were done blind or with mirrors and flash lights.

 

[Wamsutta]

From ac43-13.2b for torque on civilian non pressurized aircraft

I like that formula. Thanks for posting.

 

[budget76]

The US navy, the second largest operator of aircraft in the world allows click type wrenches with offset extensions, no correction at 90.

It appears the AF does as well as long as one doesn’t try to use the ratchet head in reverse or calibrated it both ways.

Deflection torque wrench’s are more accurate in the lab but not in the field. One can not get to a point where they can see the gauge dead on when working in the field. Just because you can on an assembly line or test cell it irrelevant to the line mechanic.

There are many jobs that were done blind or with mirrors and flash lights.

I am aware they're used ALL OVER. strictly speaking for OEM engines (Pratt and Whitney if we want to point out the company) the company holds itself tighter than from what i understand any other industry anywhere in terms of accuracy requirements. Our wrenches are calibrated to 2% of max scale reading, industry standard is 4%. our customers us clicker wrenches on the flight line.

In practice, I doubt any of us ever see a difference. especially when you throw in the viewing angle/parallax factor into beam wrenches