Torque wrench calibration

[bmwmike]

Hi

I've got two torque wrenches; a cheapie Drapet one bought about 15 years ago, and a Snap-On one my old man used to use when he had a commercial garage which must be at least 30 years old, maybe closer to 40.

Can I get these serviced and calibrated? If so any recommendations for south Wales area please.

Or is it better to buy a new one?

Thanks
Mike

[Strudul]

Can't see why not, though it may be cheaper to just buy new.

For reference, a place in Sheffield quoted £45 and £50 for a calibration up to 400 and 700Nm respectively.

[trickywoo]

What do you need to accurately torque between 400 and 700nm?

To me anything over 300 is simply bd eye popping tight.

Genuinely interested.

[E-bmw]

He didn't say HE needed to do that, he said that is what they quote to calibrate a torque wrench at anything up to that as in 0 - 200 would come in the up to 400 bracket of charges.

[Strudul]

Centre lock nuts.

[Strudul]

We have a Britool HVT5000 rated up to 560Nm, but the Carrera GT and some 911s that have centre lock nuts require 600Nm.

[finishing touch]

Hang a weight on it.

Slide a length of tube (exhaust ? ) on the handle, say 4 foot, and hang 25 lb on it. 100 ft/lb job done.


Naturally if you have a 100 lb weight then you can dispense with the tube.


Paul G

[tapkaJohnD]

Like this

John

[bmwmike]

Thanks. I am going to try calibrating it myself with the weight. I think I've even got an old flywheel laying around but failing that a brake disc or two would work.

[227bhp]

Well don't do it like that, the weight is in the wrong place.
The best way is to find out locally who does it, ask at engine builders or good quality tyre fitters and send it there for doing.
It's a precision tool which is rendered useless by back street, garden shed antics.

[Greg_D]

227bhp said:

Well don't do it like that, the weight is in the wrong place.
The best way is to find out locally who does it, ask at engine builders or good quality tyre fitters and send it there for doing.
It's a precision tool which is rendered useless by back street, garden shed antics.

well all of what you wrote is basically wrong.
if someone has a 50lb weight suspended 2 feet from the fulcrum, then the force it exerts will be exactly 100lb ft. as a quick check to +/- a couple of % it is a perfectly valid test to see if the tools remain fit for purpose. noone is proposing evidential levels of calibration.

OP: just hang a weight off it, it'll give you a decent shout...

[tapkaJohnD]

227bhp,
Greg was most polite, so I had better be the same.

Please tell how you would check a torque wrench. Where would you put the weight?

John

[227bhp]

tapkaJohnD said:

227bhp,
Greg was most polite, so I had better be the same.

Please tell how you would check a torque wrench. Where would you put the weight?

John

On the end of a crankshaft where it should be
It's just not accurate enough for me that's all.

[finishing touch]

To calibrate the calibration equipment they hang a known weight at a given distance.


I do admit that a flywheel may not be an accurately known weight.

A cube of steel 100mm x 100mm x 100mm would weigh 7.752kg and that would be a known weight.


Paul G

[Greg_D]

finishing touch said:

To calibrate the calibration equipment they hang a known weight at a given distance.


I do admit that a flywheel may not be an accurately known weight. it is if you put it on the scales first ;-)

A cube of steel 100mm x 100mm x 100mm would weigh 7.752kg and that would be a known weight.


Paul G

[227bhp]

Greg_D said:

finishing touch said:

To calibrate the calibration equipment they hang a known weight at a given distance.


I do admit that a flywheel may not be an accurately known weight. it is if you put it on the scales first ;-)

A cube of steel 100mm x 100mm x 100mm would weigh 7.752kg and that would be a known weight.


Paul G

And the scales have been accurately calibrated and also the hanging material isn't 2" wide.

After you've done all that you might as well just paid someone to do it and sat and had a beer.

[finishing touch]

By all means quote what I have said, but please do not add your words to my quote making it look as if I said it.


Don't understand the "2 inch wide" bit. Why's it relevant ?

A 20 tonne double decker bus suspended from a crane hook weighs 20 tonne, regardless of its width.

Paul G

[E-bmw]

I think what he is trying to say is that the webbing that it is suspended by in the picture looks like it could be 2" wide at the torque wrench.

Whilst the effect may be minimal (the only way to check is to do it differently to see) but if a load is spread over a distance it isn't the same as being at a precise point in the length of the torque wrench.

So, if your 12.5kg is spread over 2" of the handle it won't actually be the same as being at exactly 0.5 metre which I am guessing is what you were trying to replicate in the pic.

[MB140]

Where abouts are you op, I work in aviation and we have a couple of calibration machines we use every time we use a torque wrench.

I don’t mind popping them on our testers if your near by free of charge. Regarding servicing them though I can’t help.

[Mignon]

The method shown in the photo is perfectly acceptable although I'd suggest a couple of changes. You want to suspend your weight by a single strand of thin nylon rope which will give a more precise distance from the fulcrum where the force is being applied. Also I wouldn't be keen on heavy chunks of metal hanging there which might damage themselves or the foot they land on if they slip off. A good way of making up heavy weights is with 2 litre PET bottles from the supermarket which will weight 2 kg each filled with water. Most people have digital kitchen scales to check weights to a gram or so. Pinch a metal shopping basket from Tesco and hang that on your wrench and you can fill it with PET bottles until the ratchet clicks. It's still not going to allow calibration up to a very high torque unless you use a really long extension to the wrench handle though. A 4 foot length of scaffold pole and 25 kg of weight would do the trick though.

Having said all that the errors in torque wrenches tend to pale into insignificance compared to the lubrication value and cleanliness of the threads being torqued. Very critical fasteners like big end bolts in race engines are better fastened by the stretch method with a stretch micrometer or dial gauge.