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Torque Wrench Testing
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buzzy bee
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PostPosted: Tue Feb 20, 2007 11:17 am    Post subject: Torque Wrench Testing Reply with quote

Hi

I was wondering if there is a reliable way to test a torque wrench?

Can you do it on a torqued up nut?

Can you link 2 wrenches together with some bar on the same setting and turn in opposite directions to see if the "click" together, but wouldn't the force be halve on each wrench? I supose it would still test?

Also to do these tests you would have to have a wrench set off a master, who is to say a new wrench is acurate? (I used to test pressure gauges to a large master and new ones were very often worse than old ones)

Or is there a specialist piece of equipment to do this test for us, if so who has one and would they test our gauges, how much would it cost etc?

Cheers

Dave
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Brian M
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PostPosted: Tue Feb 20, 2007 1:35 pm    Post subject: Reply with quote

Dave

When I updated from the old style torque wrench with the pointer and plate with the settings on it, to a snap type, I tried them on various engine bolts to see how close the settings were.

I reckoned they were within plus or minus 5% of each other so considered they were accurate - but of course they could have both been giving wrong readings!
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magic9r



Joined: 13 Dec 2008
Posts: 33

PostPosted: Sun Dec 14, 2008 7:21 pm    Post subject: Re: Torque Wrench Testing Reply with quote

buzzy bee wrote:
Hi

I was wondering if there is a reliable way to test a torque wrench?

Can you do it on a torqued up nut?

Can you link 2 wrenches together with some bar on the same setting and turn in opposite directions to see if the "click" together, but wouldn't the force be halve on each wrench? I supose it would still test?

Also to do these tests you would have to have a wrench set off a master, who is to say a new wrench is acurate? (I used to test pressure gauges to a large master and new ones were very often worse than old ones)

Or is there a specialist piece of equipment to do this test for us, if so who has one and would they test our gauges, how much would it cost etc?

Cheers

Dave


The torque would be the same on both so yes, clamp one down to eliminate twist & check they are close to each other in calibration.
You could use a bar, pivot and a spring balance to test quite accurately,
Regards,
Nick
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buzzy bee



Joined: 23 Nov 2007
Posts: 3382
Location: South Cheshire

PostPosted: Sun Dec 14, 2008 9:35 pm    Post subject: Reply with quote

Hi

Since posting this a guy comes round to work and tests them, or tries to test them every year, we have to limit him to once every other year or simmilar. hehe

Cheers

Dave
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Jim Walker



Joined: 01 Oct 2008
Posts: 124
Location: Chesterfield, Derbys.

PostPosted: Mon Dec 15, 2008 12:53 am    Post subject: Reply with quote

Quite simple.

Grip the square sideways with the shaft horizontal in a vice. Set the scale (say 50 lbf ft) and hang a 50lb weight at 1ft from the square or 25 lb 2 ft from the square. If the wrench clicks below this it is weak and if it is not on the point of clicking it is too strong, but that is very unlikely. Of course if the lb ft scale is ok the Nm scale will be also.

If you do not want to buy another torque wrench, it is not difficult to determine which setting suits the job you are doing. Nor would it be difficult to compile a correction table for future use. Trying one tool or instrument against another is never a good idea and can even be dangerous with pressure gauges etc.
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buzzy bee



Joined: 23 Nov 2007
Posts: 3382
Location: South Cheshire

PostPosted: Mon Dec 15, 2008 10:05 pm    Post subject: Reply with quote

Hi

I like your idea with the torque wrenches, I supose a spring balance would work the same way, but then I supose you never know what the Spring has been calibrated to.

I have to correct you, on the pressure guage front though. Testing against a large master guage is the correct way for testing guages in industry.

It is a requirement for NSTS Testing. Smile

Cheers

Dave
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Jim Walker



Joined: 01 Oct 2008
Posts: 124
Location: Chesterfield, Derbys.

PostPosted: Tue Dec 16, 2008 1:33 am    Post subject: Reply with quote

Sorry to disagree. There is only one foolproof way to test pressure gauges and that is to use a 'Dead Weight Pressure Tester'. That resembles a weigh scale into which the gauge is screwed and the effect of any test weight placed thereon is tranferred hydraulically to the gauge. Even a 'master' pressure gauge would need testing that way frequently.

About Torque Wrenches. It occurred to me that covenient weights might not be readily available. It does not matter what weight is used as long as the distance in feet from the square x the weight in lbs agrees with the setting. I realise small torque wrenches are in inch lbs, but the same principle applies.
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Quote from my Late Dad :- "You only need a woman and a motor car and you have all the troubles you are ever likely to want". THAT was pre-computers!
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magic9r



Joined: 13 Dec 2008
Posts: 33

PostPosted: Tue Dec 16, 2008 1:57 am    Post subject: Reply with quote

There is no foolproof way, I have met hundreds of examples of evolution's ability to breed a better fool Very Happy .
No one can test a click bar type torque wrench with absolute precision as in use they are subject to feel & technique, a bar with a torque guage is a more accurate way to do it but again, not if a numpty is using it.
If you really want to get technical the only way to accurately set the force holding parts together is to measure the stretch in the bolts hence the modern practice of low torque followed by turning a number of degrees to more accurately tension the bolts. so for the purposes of most users of this board a spring balance will confirm if your wrench is reading close enough or is scrap,
Nick
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Jim Walker



Joined: 01 Oct 2008
Posts: 124
Location: Chesterfield, Derbys.

PostPosted: Wed Dec 17, 2008 10:04 pm    Post subject: Reply with quote

There is another consideration about 'degree' tightening, but I don't think that will concern anyone dealing with the cars etc. mostly dealt with on this site. That apart from the fact that data for 'degree tightening' will be hard to find for those cars.
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buzzy bee



Joined: 23 Nov 2007
Posts: 3382
Location: South Cheshire

PostPosted: Wed Dec 17, 2008 11:44 pm    Post subject: Reply with quote

magic9r wrote:
There is no foolproof way, I have met hundreds of examples of evolution's ability to breed a better fool Very Happy .
No one can test a click bar type torque wrench with absolute precision as in use they are subject to feel & technique, a bar with a torque guage is a more accurate way to do it but again, not if a numpty is using it.
If you really want to get technical the only way to accurately set the force holding parts together is to measure the stretch in the bolts hence the modern practice of low torque followed by turning a number of degrees to more accurately tension the bolts. so for the purposes of most users of this board a spring balance will confirm if your wrench is reading close enough or is scrap,
Nick


I have done a day on testing stretch in bolts, that was enough for me! Got the equipment to do it though, although I hope I never have to do it again, it is not my cup of tea.

Cheers

Dave
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buzzy bee



Joined: 23 Nov 2007
Posts: 3382
Location: South Cheshire

PostPosted: Wed Dec 17, 2008 11:50 pm    Post subject: Reply with quote

Jim Walker wrote:
Sorry to disagree. There is only one foolproof way to test pressure gauges and that is to use a 'Dead Weight Pressure Tester'. That resembles a weigh scale into which the gauge is screwed and the effect of any test weight placed thereon is tranferred hydraulically to the gauge. Even a 'master' pressure gauge would need testing that way frequently.

About Torque Wrenches. It occurred to me that covenient weights might not be readily available. It does not matter what weight is used as long as the distance in feet from the square x the weight in lbs agrees with the setting. I realise small torque wrenches are in inch lbs, but the same principle applies.


No need to apologise, Discusion is good in my eyes. Smile

This is the last I am going to comment on pressure gauges as I don't want to go on, you are correct a master guage will need to tbe calibrated, but it is made to a given and accepted tollerance. This is then quite sufficient and the most commonly used method for testing pressure gauges in industry. I have only ever seen testing done against a master gauge for normal use of gauges, but maybe you are thinking of testing the master guages. The master gauge is treaded in to a rotational valve as it the smaller gauge to be tested and then you couple this to the compressor, this can then be done in the service van.

Hope this has cleared up any confusion.

Cheers and all the best

Dave
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