torque wrench and extensions

I have a lot of bolts on my car that are completely inaccessible with a standard torque wrench. If I put a 3" extension on the wrench, I can access them. How much will this mess up the reading? Is it better to use the torque wrench with the extension, or no torque wrench at all?

Do torque wrenches with built-in extension heads exist? Man would that ever be useful...

Reply to
Ryan Underwood
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Reply to
Shep

A straight extension makes no difference and technically, I can't see how a universal swivel would make a difference either. If you think about it, take a long pipe and stick a 1' long wrench on one end and hand 1 pound from the end. That is 1 foot pound. Go to the other end of the pipe and assuming no friction (pipe on smooth running rollers) you will have to put another 1 ft. wrench on the other end with a 1 lb weight twisting the other way to counteract the first wrench and weight.. so you have 1 foot lb being exerted on the far end.

Reply to
bob

Hmm, from further study on this, it looks like extensions between the wrench head and the socket, like regular ratchet extensions, do not affect the torque applied to the fastener at all, unless the extension causes the force to be applied off-center (for example, by wobbling). This seems a little counter intuitive because the extension bar would experience at least some torsion, wouldn't it? Then you'd have to subtract the amount of torsion from the reading on the torque wrench to get the torque at the fastener.

As I understand it, with the above caveats, only extensions that modify the planar distance between the handle of the torque wrench and the fastener (such as a crow's foot) would severely mess up the torque at the fastener (by increasing it). Hopefully someone can confirm or correct this.

Reply to
Ryan Underwood

from the reading on the torque wrench to get the torque at the fastener.

You are correct. The trick in successfully using an extension on a torque wrench is to use both hands, one on each end of the wrench, to ensure the socket end stays aligned with the bolt/nut being torqued. And, of course, the wrench MUST be moving when it clicks (or the pointer reaches the desired value).

Reply to
Jerry Foster

Uh, no. It is exactly the same as pulling a rope with 100 lbs of force. This applies 100 lbs of force at the other end regardless of the rope.

Reply to
Brian Stell

Actually IF your doing any high torque measurements you do need to factor in any extensions you have added to the wrench. ALL of them will twist somewhat depending on the torque applied, size of the extension, and type of steel they are made from. Want an example of how this is used look at a set of torque sticks used with an impact gun to set wheel lug torque. They are steel extensions with the socket formed on the end, when the reach the correct torque they twist and absorb the torque from the impact gun instead of passing it to the lug nut. The different torque levels are controlled by varying the thickness of the steel between the coupler and the socket head. The higher the torque transferred the thicker the steel. Same thing occurs with normal extensions as well. Want to test your extensions, put one end in a vice and a ratchet on the other and see how far they deflect.

That is why you use bolt stretch and angle gauges for real critical torque figures.

Steve W.

Reply to
Steve W.

I am not on board with you totally on this one, Steve.

If you have a solid extension, it doesn't matter if it twists or not, the torgue at the driven end will be essentially the same as the torque at the drive end. It transmits the torque just as a fluid transfers hydraulic energy.

The extension deflects, or twists, and then stops twisting and equilibrium is reached. During the twist, a small amount of heat is mechanically generated and that is why I used the word 'essentially' above.

If the extension were to continue deforming (bending), then this would not be true, but if it just twists and comes to a stop, the torque is conserved.

Reply to
<HLS

"Steve W." wrote

Doesn't matter. 100 lb/ft applied at one end will be 100 lb/ft at the other end. (Ask an oil rig worker, with their 3-mile-long drills).

Totally different concept. Discrete impacts versus sustained force.

Irrelevant. Just move the handle a bit farther to get the reading you want.

It's still 100 lb/ft, whether the wrench handle moves an inch or a yard.

Want to test this? Get 100 feet of extensions, put a torque wrench on one end, you grab the other end with your bare hand, twist the wrench until it reads 100 lb/ft. Can you keep the extension in your hand from slipping? How about with 200 feet of extensions? 300?

Reply to
MasterBlaster

!!!!!!... glad your not workng in the engineering division of any car I buy

Reply to
Virgil Caine

I hate torque tubes, went to my tire dealer to have tires rotated, they used torque tube, later found that some lugs were torqued OVER 150ft/lbs, some were around

100ft/lbs. s> Want an example of how this is
Reply to
JR

You are correct about the torque sticks to a point. Torque from an impact wrench is generated by impact inertia or the shock of the internal hammers. Torque sticks are designed to absorb and dissipate this inertial energy thereby limiting the torque to the value of the torque stick. The energy is dissipated in the form of heat. You can feel this heat in a torque stick that has been pounded upon for a few seconds. If you use a torque stick with a regular torque wrench where the torque load or force is constant, it will work just like any other extension and transfer the torque at 100% right up to the point where it fails. For it to be said that a properly aligned extension reduces torque with a constant force torque wrench, you have to believe that energy is simply disappearing into thin air without being transferred or transformed.

Lugnut

Reply to
lugnut

A straight rope, pulled between two fastening points, will exert the same amount of force on each end in an ideal world. If you run that rope over a post, pulley block, etc the force can be altered. That is, friction in all its forms can effect the force applied. Energy is still conserved, when frictional (heat) losses are added.

Using a steel extension, if you do not rest the extension on a beam, or get the extension out of line with the bolt, or some other sort of frictional interaction, will transmit the torque without losses other that the minor and temporary heat lost in twisting. (The couple does not continue to generate heat as long as it is in torsion...Only during the deflection)

Consider it like this...you have a 20 mile piece of wire connected to nothing. Apply a voltage at one end (12V). Instantaneously, that end has 12 V potential. The 12V does not appear at the other end instantaneously, and when it does appear (at light speed after Tø), it will not immediately assume the value of 12.0000000 volts. Almost but not quite. The current effect experienced some friction and there was some loss of heat, decreasing the voltage until equilibrium can be reached. As soon as equilibrium is reached, the voltage at the end of a 20 mile wire is the same as at the start, since no current is flowing, no heat is being generated. (We neglected field effects, but the answer is still the same.)

Reply to
<HLS

IOW, if you apply 100.000 foot-pounds of torque at your handle of the torque wrench it'll probably be within 1 ft/lbs at the socket end. Not _exactly_ the same, but if it's a good torque wrench and a quality socket and extension it's essentially the same - and definitely close enough for attaching the wheels. I'd use as short as an extension as possible for engine components, but in "the real world" where people reuse dirty head bolts and don't suffer immediate catastrophic failure,

+-1% is probably good enough. Besides, when was the last time most mechanics tested or calibrated their torque wrench? :)

Ray

Reply to
ray

if it make "no" difference why do you need a short extension? hell just use a 24" 1/4 drive after all it "doesn't matter" right? or does it?

Reply to
Virgil Caine

Something like that. Your torque wrench is not accurate to 1% anyway. But if you could apply 100,000 pound feet of torque to an extension at the wrench end, and the extension did not exceed the elastic limit...that is, it does not shear off and the twisting displacement stops, then you will transfer that same 100,000 pound feet of torque to the bolt end.

Reply to
<HLS

Sure and a hundred mile rope will also have lots of side friction.

But the question was about an extension in the 4" to 2' range where there is unlikely to be any significant side friction.

Swivels are a different and much more complicated story.

Who uses 100 feet of extensions?

Reply to
Brian Stell

Longer extension makes it easier to get the torque wrench out of alignment (pivot point of the torque wrench not inline with the bolt).

If one gets the torque wrench out of alignment then the torque can vary because the force is not at the angle the torque wrench is calibrated for. The farther out of alignment the more the variance and if far enough it can be significant. Also at angles there is side friction between the bolt and the socket. It's not the extension absorbing force but a misalignment issue (same problem a swivel often has).

And a long extension can often interfere with other parts (eg: too big to fit the available space).

Reply to
Brian Stell

Exactly. Out of alignment or physical interference can effect torque transfer, but not the length of the extension as such.

Reply to
<HLS

As long as you keep the extension perfectly in-line with the axis of the bolt, it will be EXACTLY the same.

People get confused on this point because of those "torque sticks" for impact wrenches. That's a completely different scenario. Since a torque wrench applies millisecond-long pulses of torque, the torsional springiness of the torque stick will limit the observed torque at the nut. If you take the SAME torque stick and use it as an extension for a manual torque wrench, it will have absoutely no effect whatsoever on the torque applied to the bolt head, becuase the torque you apply is a constant force, not an impulse. The torque stick will twist slightly, but after its done twisting it will apply the full torque value.

Reply to
Steve

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