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#16 croc7

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Posted 12 April 2019 - 05:26 AM

In the ‘for what its worth’ department, the certification laboratory for a major aerospace company formally headquartered in Seattle requires that torque wrenches be set at 20% of max capacity after use. Has something to do with keeping a slight amount of tension on the internal spring.

#17 Pete649

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Posted 12 April 2019 - 06:44 AM

In the ‘for what its worth’ department, the certification laboratory for a major aerospace company formally headquartered in Seattle requires that torque wrenches be set at 20% of max capacity after use. Has something to do with keeping a slight amount of tension on the internal spring.

 

I hadn't heard of that one before. I always turned the torque to the minimum setting on mine (not to say I am right by doing that).



#18 Pete649

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Posted 12 April 2019 - 06:50 AM

In regards to the accuracy of the method of using a torque wrench, I found the table I was looking for;-

 

Back in my youth I did a short stint of work experience at British Rail. Looking at the table reminded me that one day I helped to change a head gasket on a loco diesel engine. The cylinder head bolts were tightened by turn of nut using a protractor attachment and a very long bar.  (Crikey - that took me back).



#19 DeadSquare

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Posted 12 April 2019 - 06:52 AM

 

In the ‘for what its worth’ department, the certification laboratory for a major aerospace company formally headquartered in Seattle requires that torque wrenches be set at 20% of max capacity after use. Has something to do with keeping a slight amount of tension on the internal spring.

 

I hadn't heard of that one before. I always turned the torque to the minimum setting on mine (not to say I am right by doing that).

 

 

I have heard of that, but I recon it is to stop ham-fisted people slackening it off so far that it all falls apart.



#20 Ethel

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Posted 12 April 2019 - 06:55 AM

Interesting chart. Why does it cost twice as much to count flats as buy a torque wrench???

Makes me wonder if there's any worthwhile "operator procedures" to improve accuracy? Is torque wrench preheating going too far ?

#21 Spider

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Posted 12 April 2019 - 07:22 AM

Most of the Band of Accuracy Range (or error) with using a Torque Wrench is not the wrench itself, we've all seen accuracy / repeatability figures of the wrenches themselves in the +/- 3% range or better.

 

Most definitely, great in-accuracy can be 'dialed in' by haphazard use and application (technique) of the wrench.

 

But, these figures in the chart assume the Monkey on the Wrench know's what they are doing and where this wide range actually comes from is friction. Friction of the threads and friction of the the faces between the fastener and the member.

 

Further 'error' is also 'dialed in' with Bolts as opposed to Studs and Nuts. Some of the applied Torque is taken up in the twisting over the length of the Bolt, down to where the friction of the Threads is.



#22 GraemeC

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Posted 12 April 2019 - 07:34 AM

Interesting chart. Why does it cost twice as much to count flats as buy a torque wrench???

Makes me wonder if there's any worthwhile "operator procedures" to improve accuracy? Is torque wrench preheating going too far

 

I presume the 'cost' is simply looking at the time factor of installing the fastener, in which case I can quite easily see how counting the flats or a prescribed angular rotation can take longer than simply swinging on a (pre-set) torque wrench.
If on some assembly line seeing 100's of fasteners being installed a day, it would be a quite major labour cost increase.



#23 DeadSquare

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Posted 12 April 2019 - 08:02 AM

Why do we use a torque wrench ?

 

To stop the bolt/stud being stretched and thus weakened.

 

But what we are actually testing is friction along the threads and between the bolt head/nut, against the face it is gripping.

 

The Royal Radar Establishment at Malvern used Binx nuts, and so a torque wrench was useless.

 

They used precision washers with a crushable indent.

 

The thread is tightened until there is enough pressure/strain to flatten the indent, irrespective of how much friction there is in the thread.

 

A torque wrenche's only use is to limit the force applied, so that a bolt/stud does not shear when being undone.


Edited by DeadSquare, 12 April 2019 - 08:03 AM.


#24 Spider

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Posted 12 April 2019 - 09:02 AM


But what we are actually testing is friction along the threads and between the bolt head/nut, against the face it is gripping.

 

 

That does definitely occur and is probably the most part of what is being gauged against, but - theoretically - it's also measuring the force (torque) needed to shove a load up a ramp (or incline).



#25 GraemeC

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Posted 12 April 2019 - 09:07 AM

I would say a torque wrench is used to 'ensure' the fastener IS tightened to the point that it stretches, but not beyond its elastic limit and into plastic deformation.

 

A threaded fastener needs to be stretched in order to reliably maintain a clamping force.  It is this that means secondary locking techniques (such as spring washers, nyloks etc) are not needed for head nuts, big end bolts.....



#26 DeadSquare

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Posted 12 April 2019 - 09:34 AM

I would say a torque wrench is used to 'ensure' the fastener IS tightened to the point that it stretches, but not beyond its elastic limit and into plastic deformation.

 

A threaded fastener needs to be stretched in order to reliably maintain a clamping force.  It is this that means secondary locking techniques (such as spring washers, nyloks etc) are not needed for head nuts, big end bolts.....

 

Where the clamping force was the predominant need, RRE  used a dished washer, like a dinner plate, and it was crushed until the gap round the rim reached a certain prescribed gap that was measured with a feeler gauge.



#27 nicklouse

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Posted 12 April 2019 - 11:38 AM

well, 3 torque wrenches bought. 5-25Nm 10-50Nm and 40-200Nm all to DIN/EN ISO6789. will be adding one more later to cover stupid tight things.



#28 Ethel

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Posted 12 April 2019 - 12:22 PM

I would say a torque wrench is used to 'ensure' the fastener IS tightened to the point that it stretches, but not beyond its elastic limit and into plastic deformation.

 

A threaded fastener needs to be stretched in order to reliably maintain a clamping force.  It is this that means secondary locking techniques (such as spring washers, nyloks etc) are not needed for head nuts, big end bolts.....

Big ends make a good case study. The fasteners need to stay within the elastic limit, including with the extra load of the pistons trying to fly out the top of the bores at tdc. On the flip side, the closer you are to the elastic limit the better it'll resist fatigue from cyclic elongation. The free length and thickness between loading points (head and nut) are also factors.



#29 Icey

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Posted 12 April 2019 - 01:03 PM

well, 3 torque wrenches bought. 5-25Nm 10-50Nm and 40-200Nm all to DIN/EN ISO6789. will be adding one more later to cover stupid tight things.

 

What did you go for and what's the first impression? (I really need to replace mine).



#30 nicklouse

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Posted 12 April 2019 - 01:13 PM

 

well, 3 torque wrenches bought. 5-25Nm 10-50Nm and 40-200Nm all to DIN/EN ISO6789. will be adding one more later to cover stupid tight things.

 

What did you go for and what's the first impression? (I really need to replace mine).

 

nothing you will find in the UK unless someone rebadges them. made in Germany.

 

odd it is in Dutch when the language is set to English

https://www.nordwest...mentschluessel/

 

did ask Halfords if they could ship to Germany but nope.

 

will be testing them later. what is "nice" is the 1/4 drive is actually a 3/8 and 1/4 drive so I can switch it between two tools or use the 3/8 out of my old one in it.






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