When I started working on VW's, I was told by a very competent mechanic that whenever one uses an extension on a torque wrench, to set the wrench to 5 lbs higher than you would normally. 5 lbs for each extension.
Later, I asked him about deepwell sockets. He looked at me for a minute, then said he saw no reason to change for them. The 5 pounds is not for the length, but for the flex that happens in each socket joint.
I've been using this for a few years now with no noticed problem...anyone have any comments?
david · keen_at_finally.atlasta_dot_net
Raistrick put you guys up to this didn't he . . ? :-)
First he goes by with the bait, then a couple of you throw rocks.
Then you get "physicsdude" AKA "thingguy" to light a smoke pot near my hole . .
OK . . . I'm awake and totally pissed off . . . ! :-)
That A/A+B = Torque is if you put a crows-foot on the end of the torque wrench . . . "old handle/new handle . . ? a ratio
Another example is the "slugging wrench" for the rear axle nuts. It has a 1/2" drive socket in it that is 3-1/2" from the center of the nut. . . . need to do that ratio thing that "thingguy" brought up . .
Assuming the 6" from "thingguys" example, a 200 ft-lb torque on a 6" extension would give you 285 ft-lbs . . . It's a way to get more torque from your wrench than it's rated for.
Putting an extension or "cheater bar" on the handle end is not the same . . for that, you continue to read the gauge . . (bad)
David, however, was talking about an extension for the socket . . That which gives you an offset position for the wrench from the socket . .
For that we would have a torque loss equation . . .
You apply 50 ft-lbs of torque to a six inch extension to the socket . . the extension is steel and steel is still the most "elastic" material we have . . . .
Elasticity is defined as the amount of load that can be applied to a material under certain constraints and the material will return to its original shape . . .
So that extension is a spring . . . in our case, it is a "torsion spring" . . .
When you apply your force, the "spring" starts to wind up . .
When the spring rate reaches equalibrium with the force required to move the nut, then torque will be applied to the nut . . As it gets harder to turn the nut the spring must first "wind up" or deflect radially until a new equalibrium is reached. . .
The amount exerted to the nut will always be "less the amount used to deflect the shaft around it's axis" . . .
The torsion spring rate is relative to material spring rate times the cross-section of the shaft times the length of the shaft. .
You notice this when you are trying to loosen a nut with a long extension . . you get a lot of angular movement before you get the damn thing wound up enough to break that nut loose. . . Makes it almost impossible to use an extension on a impact-wrench.
I have this friend who is a power tool freak . . he's pulling a tranny from a ford SUV . . . he's clear behind the car, with about a four foot extension made up of about five pieces and he'e got an impact wrench on it to break a bolt loose up on the tranny. . . :-) Might as well beat it with a flower . . . :-) He doesn't take well to criticism so I left him to it . . :-)
So the spring is relative to the material of the extension and the diameter of the shaft and the length of the shaft times the force.
Going thru the numbers for a standard 1/2" shaft and 6" long, 5 lbs might be a good number for the 50 lbs in . . .
Only when you apply ten pounds or 150 lbs . . the number needs to change . . .
Without resorting to math, I'll tell you how to figure the spring rate for your extension . .
For a 1/2" drive torque wrench, get a 1/2" bolt and nut . . Get some lock washers and flat washers, 2 or 3 . . . If you have a pipe spacer, throw that in too . . Get a bolt about as long as you can set in the jaws of your vise.
No vise . . ? well you're SOL aren't you . . ? :-)
The idea of the longer bolt is that it's a spring when it's pulled too . . the longer it is the more movement for a given force . .
Put the nut in the vise . . thread all that garbage on the bolt, put a flat washer between each lock washer and the faces of the nut and bolt-head . . .
Get a pair of calipers and your 12" extension bar . .
Put the extension on the torque wrench and torque the bolt down to a good number for a 1/2 or 13mm bolt . . . 50-80 ft-lb . .
Now take a measurement over the head to nut with the calipers.
Take the extension off and using the same number for tightening, see if you move the nut . . . bets are you will . .
If you can't tell if it moves, mark it with an index mark, nut to bolt . . .
Also take another measurement over-all. . . it got shorter.
Now start adding a pound or five to the reading/extension and testing with the real number w/o extension till it stops moving . . the measurement stays the same . .
You will have to do a series of tests relative to the torque to work out a sliding scale you can use. As in "add a pound for each 20 lbs of torque" . . .
Let's forget the whole thing and go get big heavy extension.
I have this maybe six inch extension for wheel nuts, etc. . .
It's 3/4 inch and looks like a nose-tackle . . :-)
Then I got a 3/4 X 1/2 short adapter to get me to my socket.
Has a spring rate of about 150 lbs on an 8 ft cheater bar. .
Oh, the number of socket connections is just slop to a torque wrench, no big deal other than the thing wants to bend all which way . . To an impact wrench it would be important if the spring rate didn't already defeat its purpose . .
None of this could be categorized a "sin" . . A sin is if you cause another un-necessary pain . . causing yourself pain is just stupid. :-)
west :-)