Torque Wrench questions?

[Bret]

Ok not directly related to LBCs but I do have a tool question for a work project I am investigating right now.

Specifically "torque wrench calculations” when using extensions and/or adapters, will they affect the selected torque settings?

Here is what I am dealing with – we are getting some failures of a slip torque limiter that is required to protect a boom from collisions and over extentions. Rather than breaking something under those conditions it is intended to slip. Problem is when it slips it should be easy to release the bolts and realign the boom and then torque the bolts again. However what is happening is it is seizing up and making resetting a real pain. I suspect one of the following conditions is the root cause – the bolts have been over-torqued one too many times (i.e. stretched) and need replacement. Or they are not being “evenly” torqued by the operators and techs.

The procedure requires a setting of 40lbs on 9 bolts. Using a mechanical (“click type”) torque wrench with a 1/2” drive with a 3/8” adapter and a socket. However sometimes other things get in the way during the procedure and require a 4” or a 6” extension to reach the heads of the bolts.

I realize that extensions do have some affect, but I ain’t that sure how much or how to calculate it. Moreover at 40lbs I’m not even sure it really matters.

Oh & before someone asks the wrenchs are calibrated regulary and the cal reports indicate all came in well within specs.

Thoughts?

 

[John Loftus]

Hi Bret,

Extensions will make a big difference on the actual torque applied. A 12" wrench with 6" extension will only need 26.66 ft/lbs to reach an actual 40 ft/lbs. There's a good overview and calculator at:
https://www.norbar.com/faqs.php

Also if you search Google for "torque wrench extension calculations" you can download converter programs for your computer or palm. The math is pretty simple though.

Cheers,
John

 

[PC]

Cool link John! A company that was created to make torque tools for assembling Merlins, /ubbthreads/images/graemlins/england.gif

Bret, does the procedure for reassembly specify the pattern and sequence for torquing the bolts? I find that operators must be trained to do it and have a written procedure and/or diagram. It's not a natural behavior (unless you're an engine guy I guess). Most people just start at one point and move to the next closest, tightening to full torque each time unless they're trained otherwise.

If the extension is an open-end, length or offset extension like the one shown in the Norbar diagram the calculations are appropriate. A socket extension won't change the torque value but it's critical to hold it square with the wrench drive feature centered on the bolt axis.

I presume that the bolts are holding tension on some kind of friction surfaces, whether a traditional friction material or simply metal. If the planes of the bolting seats and slip faces aren't perfectly parallel any slippage will cause changes in load tension. Since bolt stretch is normally thousandths or tenths it doesn't take much out-of-parallel to make a huge change in tension in an all metal assembly. If a layer of friction material is providing the preload it would depend on the ratio of out-of-parallel to material compression.


PC.

 

[gonzo]

These post are very informative, but I have a related question that's less technical.

The ratchet mechanism on my “off-brand” torque wrench has failed after about 25 yrs of service. Purchased for $32, it carried a life-time guarantee and was probably one of my first serious tools. I’m attached to this thing and rather repair than replace, but removing the ratchet mechanism is not intuitive – there’s no C clips or pins etc. It may be time to replace.

The ½ in. drive from Sears is a disappointment (1 yr limited warrantee) has plastic components and not to their typical standard. Two wrenches from SK have ranges of 20 to 150 FTLB and 25 to 250FT/LB, respectively. The max 150FT/LB should be fine for most general work, but for our LBC, would there an occasion to torque something beyond 200? Any suggestions would be appreciated. Thanks, GONZO

 

[John Loftus]

[ QUOTE ]
The max 150FT/LB should be fine for most general work, but for our LBC, would there an occasion to torque something beyond 200? Any suggestions would be appreciated. Thanks, GONZO

[/ QUOTE ]

Hi Gonzo,

The highest value I see in the workshop manual (torque wrench setting section) is for the Pinion bearing nut. 1680 lb/in which is 140 lb/ft. The next highest is main bearing nuts 900 lb/in or 75 lb/ft. Sounds like a 150 would cover everything.

Cheers,
John

 

[Steve_S]

I have one Sears torque wrench and one Snap-On. I will never buy a Sears again, and when I've finally had it with the Sears, it will get replaced with a second Snap-On. Yes they are expensive but they are the last torque wrench you will ever buy, and they will be around in 40 years should it actually fail.

I was going to answer the original question but it's definately been covered. PC said everything I was going to say and more.

 

[gonzo]

Hi John and Steve S.

Hi John!
Thanks for the references - 140FT/LBS - right on!

Steve S.
Thanks for confirming my suspicions about Sears product: certainly not to standards.

Did a search and found The Tool Warehouse featured quality SK Torque Wrenches at discounted prices, so two were purchased: 3/8 in. drive @ 10 to 100FTLBS and 1/2 in. drive @ 20 to 150FTLBS. No state tax and free shipping sweetened the deal.

And speaking of sweet, told my wife I bought one just for her. We're both so happy! GONZO

 

[78Z]

[ QUOTE ]
[ QUOTE ]
The max 150FT/LB should be fine for most general work, but for our LBC, would there an occasion to torque something beyond 200? Any suggestions would be appreciated. Thanks, GONZO

[/ QUOTE ]

Hi Gonzo,

The highest value I see in the workshop manual (torque wrench setting section) is for the Pinion bearing nut. 1680 lb/in which is 140 lb/ft. The next highest is main bearing nuts 900 lb/in or 75 lb/ft. Sounds like a 150 would cover everything.

Cheers,
John

[/ QUOTE ]

The torque needed for the flywheel nut on my Rx-7 is a eye popping 350 ft-lbs with a 54 mm or 2-1/8" socket! /ubbthreads/images/graemlins/eek.gif

I hope I never have to mess with that one.