Accuracy of torque wrenches?

[TheOtherLeft]

Does anyone know how accurate torque wrenches are?

I have a 1/2" SWG torque wrench that I'm starting to use more and wonder just how accurate it is. I have no intention of getting it calibrated due to the cost factor though.

[DUDELUX]

For the price of them, theyed want to be as accurate as possible.

[ledgend80]

we get ours calibrated at work and was speaking to the guy who was calibrating them and he said stay away from some of the cheaper ones as they are not the accurate and some he cannot get back into spec (including the new ones)

[drr]

Yep, comes down to quality of torque wrench. We just bought some at work for $450 each, they are 1/4" drive and are permanently set to 1Nm. They are accurate to about 3% going by the calibration certificates. Others are meant to be about 6% I think.

[Ice]

unless your the one thats taken it out of the box with the calibration certificate, you dont know whats been done with it

[drr]

unless your the one thats taken it out of the box with the calibration certificate, you dont know whats been done with it

One of those new ones I was talking about got dropped from 20m up in the scissor lift, first time it got used. When they lowered the lift there was a loud bang. Found the torque wrench in the base of the scissor, not too bad but the socket off it had been crushed by the scissor arms. May need a new calibration certificate.

[sprungupcruiser]

I've picked old snap on torque wrench, made in 1986 i think, it came with original box and instructons. It's got the dial in middle of it which i'd never seen before, i don't really need it calabrated, but i'd like to see how accurate it is. Is there an easy way to do this?

[DamTriton]

I've picked old snap on torque wrench, made in 1986 i think, it came with original box and instructons. It's got the dial in middle of it which i'd never seen before, i don't really need it calabrated, but i'd like to see how accurate it is. Is there an easy way to do this?

Send it back to Snap-on. If it is out of calibration they should supply a new one as a part of their lifetime guarantee. Check with them first, but they are usually pretty good.

[-Scott-]

Torque = Force x radius

Force = mass x G (gravitational constant = 9.81 or thereabouts)

Find largish wheel (27" bicycle wheel?) , mount solidly to axle. Mount axle in "frictionless" bearings, so that axle & wheel spins freely.

Run rope around wheel, and tie to weight on ground.

Use torque wrench to turn axle to lift weight. Determine the setting/reading at which torque wrench can no longer lift weight.

Torque = mass (in kg) x radius (in metres) x 9.81

That's the theory. Test it for me?

[chunderlicious]

For the price of them, theyed want to be as accurate as possible.

SWG isnt an expensive torque wrench.

if in doubt put a drop or 2 of 243 on the thread. bolts have a torque allowance for the torque wrench, not the bolt.

[-Scott-]

if in doubt put a drop or 2 of 243 on the thread. bolts have a torque allowance for the torque wrench, not the bolt.

Huh?

To quote our (in)famous ex-pat, "Please explain?"

[sprungupcruiser]

I've picked old snap on torque wrench, made in 1986 i think, it came with original box and instructons. It's got the dial in middle of it which i'd never seen before, i don't really need it calabrated, but i'd like to see how accurate it is. Is there an easy way to do this?

Send it back to Snap-on. If it is out of calibration they should supply a new one as a part of their lifetime guarantee. Check with them first, but they are usually pretty good.

Thats a good idea, might be $40 well spent. haha

Torque = Force x radius

Force = mass x G (gravitational constant = 9.81 or thereabouts)

Find largish wheel (27" bicycle wheel?) , mount solidly to axle. Mount axle in "frictionless" bearings, so that axle & wheel spins freely.

Run rope around wheel, and tie to weight on ground.

Use torque wrench to turn axle to lift weight. Determine the setting/reading at which torque wrench can no longer lift weight.

Torque = mass (in kg) x radius (in metres) x 9.81

That's the theory. Test it for me?

Stuff that, I like the first idea better. You lost me torque.

[phippsy]

We've had ours recalibrated at work in the last few weeks, I'll check the invoice too see how much we paid for interests sake.

[mick80]

Torque = Force x radius

Force = mass x G (gravitational constant = 9.81 or thereabouts)

Find largish wheel (27" bicycle wheel?) , mount solidly to axle. Mount axle in "frictionless" bearings, so that axle & wheel spins freely.

Run rope around wheel, and tie to weight on ground.

Use torque wrench to turn axle to lift weight. Determine the setting/reading at which torque wrench can no longer lift weight.

Torque = mass (in kg) x radius (in metres) x 9.81

That's the theory. Test it for me?

i got a headache now better get another beer
lol
cheers mick

[drr]

I've picked old snap on torque wrench, made in 1986 i think, it came with original box and instructons. It's got the dial in middle of it which i'd never seen before, i don't really need it calabrated, but i'd like to see how accurate it is. Is there an easy way to do this?

Find someone with a nice new calibrated one, do up one bolt with yours and one bolt with theirs. Then see if either one will tighten the other bolt at all. Repeat this a few times to get consistent results. Should give a rough indication of how accurate your wrench is.

[thehanko]

can you not just get bolt, put it in a vice, so it will not move.

fit the torque wrench to the bolt head.

measure out a nice neat number from the center of the head to somewhere on the handle (further out the better for greater accuracy). attache a fish type set of hanging scales to this point on the handle.

lets use the example of 400mm as mine has a 400mm handle - 0.4m

get a fish weight, say 5kg.
f=ma
f=5 x 9.8
f=49N

T (torque) = md Where d is the perpendicular distance from the point of rotation. in this example 0.4meters

T = 49 x .4
= 20Nm

or with 10kg pull? 40Nm

this might be too low for your torque wrench to test. but the idea is that you set it to 20Nm and see it it clicks when you pull on the fish scale and it reads 5kg.

Should give you a fairly good idea of its accuracy, i.e if it clicks at 4.5kg its 10% out. if it clicks at 4.9 or 5.1kgt then its 2% out.

[BlueSuzy]

We drop ours all the time at work..

[ANDREWGQ 351]

Get a callibrated torque wrench and a bit of hex bar, put your torque wrench with socket on it onto one side of the hex bar and do the same on the other side of the hex bar with the callibrated torque wrench,
set both to 100 N.m.
Pull both together then match your setting to the callibrated one at 100 N.m so yours goes off when it does, the difference of yours to the callibrated one is the percent difference.
I just got mine checked at a local engine reco shop and found that my 10 yr old snap on was 4% high, the guy tested for free and only took 2 mins

[WRXZook]

If you are going to check the calibration of your torque wrench, don't just check it in the lower range because it may not be all that consistent across the range. When I was doing calibration of flight line tension wrenches they were tested every month and at every 10 ft lbs right across the range and some can be much less accurate down low and up high. I have 4 tension wrenches (all different ranges) and only use one that is most suited for the tension being applied, ie. don't use a 200 ft lb wrench if only tensioning to 25 ft lbs etc. Yours may be accurate in that instance, but many aren't.

[KiwiBacon]

First question is why? What are you doing that is that critical?

The reason I ask, is that torqueing up bolts isn't an exact science, attempting to completely control the torque can still result in bolt tension being wildly different.

[hulsty]

According to my little engineers black book, using a torque wrench yields bolt torque results of + or - 25% !!

To get somewhere accurate + or - 4% check bolt elongation.

The wrench itself may be accurate but what about the installation technique etc?

[dogbreath_48]

According to my little engineers black book, using a torque wrench yields bolt torque results of + or - 25% !!

To get somewhere accurate + or - 4% check bolt elongation.

The wrench itself may be accurate but what about the installation technique etc?

What does your little engineers black book have to say about lubricated threads vs. dry threads?

[chunderlicious]

if in doubt put a drop or 2 of 243 on the thread. bolts have a torque allowance for the torque wrench, not the bolt.

Huh?

To quote our (in)famous ex-pat, "Please explain?"

243 is medium strength loctite blue in colour , it is the one that should be used on bolts that MAY be needed to come undone in the future.


EDIT: lubricated vs. dry threads is something that manufacturers of different bolts decide for themselves. CAT bolts are a non lubed bolt where as some of the hitachi bolts MUST be oiled before tensioning. But lubricated bolts do tighten/elongate something rediculous like 25% more than a dry bolt at a certain tension.

[-Scott-]

if in doubt put a drop or 2 of 243 on the thread. bolts have a torque allowance for the torque wrench, not the bolt.

Huh?

To quote our (in)famous ex-pat, "Please explain?"

243 is medium strength loctite blue in colour , it is the one that should be used on bolts that MAY be needed to come undone in the future.


EDIT: lubricated vs. dry threads is something that manufacturers of different bolts decide for themselves. CAT bolts are a non lubed bolt where as some of the hitachi bolts MUST be oiled before tensioning. But lubricated bolts do tighten/elongate something rediculous like 25% more than a dry bolt at a certain tension.

My bad. I should've been more specific. This bit:

bolts have a torque allowance for the torque wrench, not the bolt.

And now, this bit:

But lubricated bolts do tighten/elongate something rediculous like 25% more than a dry bolt at a certain tension.

[KiwiBacon]

According to my little engineers black book, using a torque wrench yields bolt torque results of + or - 25% !!

To get somewhere accurate + or - 4% check bolt elongation.

The wrench itself may be accurate but what about the installation technique etc?

Pretty much my point. There's no point having a torque wrench that's accurate to +/- 1% when the final result is still +/- 25%.

Unless you're installing helicopter blades, it's probalby not necessary.

[oldmate]

measure out a nice neat number from the center of the head to somewhere on the handle (further out the better for greater accuracy). attache a fish type set of hanging scales to this point on the handle.

That works in theory, but your fish scales would have to be equally accurate

[thehanko]

measure out a nice neat number from the center of the head to somewhere on the handle (further out the better for greater accuracy). attache a fish type set of hanging scales to this point on the handle.

That works in theory, but your fish scales would have to be equally accurate

are you saying that last 60 pound jew might have only been 50? you bastard! or you could be saying it might have been 70 - lets roll with that.

good point, compounding inaccuracy.

[chunderlicious]

if in doubt put a drop or 2 of 243 on the thread. bolts have a torque allowance for the torque wrench, not the bolt.

Huh?

To quote our (in)famous ex-pat, "Please explain?"

243 is medium strength loctite blue in colour , it is the one that should be used on bolts that MAY be needed to come undone in the future.


EDIT: lubricated vs. dry threads is something that manufacturers of different bolts decide for themselves. CAT bolts are a non lubed bolt where as some of the hitachi bolts MUST be oiled before tensioning. But lubricated bolts do tighten/elongate something rediculous like 25% more than a dry bolt at a certain tension.

My bad. I should've been more specific. This bit:

bolts have a torque allowance for the torque wrench, not the bolt.

And now, this bit:

But lubricated bolts do tighten/elongate something rediculous like 25% more than a dry bolt at a certain tension.

All information told to me by loctite and drilled into my head by CAT at various times. both companies said to ask manufacturers of the bolt as to lubricate or not. both said lubricated bolts stretch a rediculous amount more than dry for a set torque and both said (but mainly cat) that the torque range of a bolt (e.g. 1/2" is 75lb. ft. +/- 10 lb. ft.) is because A. not every bolt will be at the right tension at that exact spot and B. because every torque wrench is slightly different.

if im wrong, so be it, i wont comment on anything like this again but this is the info myself and 20 others are getting on a yearly basis from these companies and our main equipment is CAT so why would they lie?

[-Scott-]

All information told to me by loctite and drilled into my head by CAT at various times. both companies said to ask manufacturers of the bolt as to lubricate or not. both said lubricated bolts stretch a rediculous amount more than dry for a set torque and both said (but mainly cat) that the torque range of a bolt (e.g. 1/2" is 75lb. ft. +/- 10 lb. ft.) is because A. not every bolt will be at the right tension at that exact spot and B. because every torque wrench is slightly different.

if im wrong, so be it, i wont comment on anything like this again but this is the info myself and 20 others are getting on a yearly basis from these companies and our main equipment is CAT so why would they lie?

Calm down. I'm not suggesting you're wrong. I couldn't understand what you were trying to say. I'm starting to understand now.

[KiwiBacon]

But lubricated bolts do tighten/elongate something rediculous like 25% more than a dry bolt at a certain tension.

All information told to me by loctite and drilled into my head by CAT at various times. both companies said to ask manufacturers of the bolt as to lubricate or not. both said lubricated bolts stretch a rediculous amount more than dry for a set torque and both said (but mainly cat) that the torque range of a bolt (e.g. 1/2" is 75lb. ft. +/- 10 lb. ft.) is because A. not every bolt will be at the right tension at that exact spot and B. because every torque wrench is slightly different.

if im wrong, so be it, i wont comment on anything like this again but this is the info myself and 20 others are getting on a yearly basis from these companies and our main equipment is CAT so why would they lie?

The long and the short of it is:
The goal is bolt tension, torque wrenches can only measure torque.

The relationship between torque and tension depends on a lot of factors, lubrication and bolt finish being the major ones.

Bottomline. Torque wrenches are only a guide.