Torque Wrench

skivenov

molerat wrote: »

How do you know that any torque wrench is accurate ? I have seen incredibly expensive ones that are way out.

Fairly easy really. My mate works at a large-ish bodyshop, they periodically have to check their workshop torque wrenches against a control one that gets left in a locked cabinet and only used for that purpose.

You tighten a bolt to a measured figure with the control wrench, check the workshop wrench clicks at the same tension or measure how far you have to wind it on to make it click. Then you tighten a bolt to a known figure with the workshop wrench, and check the control wrench clicks on it, or how far you you have to wind it on.

Then you repeat on a few other torque values.

Then periodically, they have the control wrench calibration checked.

I just drop mine in with a few tins about once a year when they're checking the workshop ones. It's a bit out, but not massively, and it's consistant, so I know what to set it to to get the right real world reading.

TrickyWicky

londonTiger wrote: »

I was inded trying to torque it backwards when I did my initial test.

I don't know whats worse.. cheap TWs or the idiots that try to test them not having a clue :rotfl:

One things for sure, I wouldn't trust you with a potato gun

londonTiger

TrickyWicky wrote: »

I don't know whats worse.. cheap TWs or the idiots that try to test them not having a clue :rotfl:

One things for sure, I wouldn't trust you with a potato gun

thanks a lot buddy, appreciate the kind words.

TrickyWicky

Don't take it so personally.. at least you know the damn things works right?!

londonTiger

TrickyWicky wrote: »

Don't take it so personally.. at least you know the damn things works right?!

you're an idiot, i wouldn't trust you with a potato gun, but don't take it personally he says.

colino

skivenov the test at his place was obviously set up with good intentions but cant be considered of any real value. A protocol using the tool at the correct, repeatable test temperature and after using the tool at its highest value 5 times before using whatever standard, or most common setting (in a bodyshop?) against a test piece is minimum needed after 12 months or 5000 cycles. Using it against another, though rarely used, tool plus factoring in hysterisis wouldn't point at true, accurate forces, just indicate both tools are equally inaccurate

Wig

londonTiger wrote: »

Thanks for pointing that out to me,

No problem hats off to you for admitting you made the mistake.

The test corroborates the torque wrench test certificate - i.e. torque is correct to 4% and in this case it takes a little less torques than stated to make it click

I would be satisfied with those results aswell. But I would now try to make a conversion chart, for each 10Nm point on the scale. And being a bit obsessive I would try to measure the turning force of the TW itself to add to your test weight, you won't have a gravity spring scale accurate enough, so I would....
Hold the wrench horizontal, holding it by the square drive or by a socket on the square drive.
Turn the wrench/ratchet so that the handle will drop down to vertical when released.
Then -whilst holding it horizontal- place the handle end onto an accurate scale such as an electronic one in the vegetable section in some Tescos or your own digital kitchen one.

The weight indicated should then be added onto any weight you test with. It may only be about 400 grams but I think it's worth knowing.

I think I'll test my TW too.

Norman_Castle

I checked mine with one of these
http://www.ebay.co.uk/itm/40kg-x-10g-Electronic-Large-LCD-Portable-Digital-Scale-For-LUGGAGE-FISHING-UK1ST-/330681135500?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item4cfe21b18c
hung 12" from sq drive centre (no maths). Easily checks various settings. Set wrench , pull on hook, note when it lets go. Accurate compared to post office scales. Much more accurate than uncalibrated weights checked on bathroom scales.
Absolute accuracy of all manually set torque wrenches is unlikely due to setting variables.

TrickyWicky

londonTiger wrote: »

you're an idiot, i wouldn't trust you with a potato gun, but don't take it personally he says.

Because you're prone to making blunders. Thats how many people are. It doesn't mean you're unlikeable as a person it just means I wouldn't trust you not to break something or misunderstand it.

molerat

skivenov wrote: »

Fairly easy really. My mate works at a large-ish bodyshop, they periodically have to check their workshop torque wrenches against a control one that gets left in a locked cabinet and only used for that purpose.

You tighten a bolt to a measured figure with the control wrench, check the workshop wrench clicks at the same tension or measure how far you have to wind it on to make it click. Then you tighten a bolt to a known figure with the workshop wrench, and check the control wrench clicks on it, or how far you you have to wind it on.

Then you repeat on a few other torque values.

Then periodically, they have the control wrench calibration checked.

I just drop mine in with a few tins about once a year when they're checking the workshop ones. It's a bit out, but not massively, and it's consistant, so I know what to set it to to get the right real world reading.

This is how you do it properly but a bit OTT for the average DIY job http://www.ebay.co.uk/itm/Acratork-L3-Autostop-Torque-Calibration-Analyser-500ft-lb-675-NM-/230925927597?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item35c44204ad
Had 3 in our workshop so always 2 in use with the third on cal.