Hello
I want to buy a torque wrench and I have read a car mechanics article recommending the halfords one.
However, I see the draper one is half the price and the error rate is 2.29% compared to 1.14% that Halfords one achieved. Also, the screwfix one has an error rate of 3.09% but only costs £14.51.
I have listed the sites below. Can anyone advice me please?
There is a Draper one on this site:
www.amazon.co.uk/Draper-30357-micrometer-adjustmen...m
www.screwfix.com/prods/18289/Hand-Tools/Spanners-W...h
Thanks
Greg
Edited by Dynamic Dave on 08/05/2009 at 13:29
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Buy the best you can afford - Halfords sell some good tools at a good price (that doesn't mean that all their tools are good though!)
I have one old torque wrench that looks identical to the draper - including the box. I would be amazed to find its accuracy to be better than 3 percent.
How many torque wrenches of each type did Car Mechanics test ?
If it was only one of each, then the test is not that meaningful - also that accuracy may not be maintained over multiple uses, or time.
I also have a newer torque wrench than my old one - I must get them calibrated some time :-) The newer one was more expensive and much easier to use than the old draper - it's also much smaller which can an advantage where space is at a premium.
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Where do you get torque wrenches calibrated?
Are there any specialist firms?
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Did the Car Mechanics article even mention that in installing a fastener you're trying to preload it, to stretch it, and that the bolt torque is just an indirect way to measure that?
My guess, considering the standards of that particular publication of late, would be not.
Unless you're a pro, and working on lots of cars, don't worry too much about getting the last degree of accuracy from a torque wrench - it's not a good way to spend your money. Anything less than 5% will be fine.
Despite involving the use of a seemingly precise instrument, the process of torquing bolts up isn't a particularly precise way of installing fasteners. There's so much variation caused by friction in the threads, and under the head of a bolt that a bit off error in the torque wrench is truly trivial.
Even with a top quality wrench, calibrated imediately before use, and a very well trained and experienced operator, I've measured scatter of over 25% between installed fastener preloads.
If the preload of a bolt is really critical, it gets a torque plus angle tightening specification.
The main thing to get right is the range of the device. Look at the bolts you're going to be tightening, and see what torque they are set to, and make sure these values fit well within the range of the wrench.
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Where do you get torque wrenches calibrated? Are there any specialist firms?
Yes there are, but usually they deal with companies only. Most garages with any sort of quality system,will have a "master" torque meter which is used to compare readings before the torque wrench is used. This master is usually calibrated by a specialist company every year or so. It's worth a call to your local garages, to ask them to test yours for you. It takes only a minute to test at 25%, 50% and full capacity. As a private individual, you will not require a certificate. The price of a pint would do. I could sort you out if you were local to me.
Regarding makes, "Norbar" are good robust wrenches, I have one 25 years old, and never needed adjusting.
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Does it really matter?
As NC pointed out, measuring the tightening torque is a very crude way of accurately deciding how tight a fastener should be, but it's perfectly acceptable for the crude mechanics of a car.
When I was a lad (eyes raise mistily) an old mechanic taught me the correct torque was what you could apply with two fingers around the end of the proper spanner for the job.
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The old ways still work for me, I can "set my elbow" and get the tightness about right on lots of fasteners.So does it really matter? Yes it does. Compare a mechanic with 40 years experience to an amateur who wants to DIY to save a few quid. The amateur will make a better job using a torque wrench. Lots of stretch bolts, aluminium castings and modern gasket materials really demand accuracy and a decent torque wrench will give this. Ever tried to remove a wheel at the side of the road, when the bolts have been "razzed" up by a tyre fitter with his air wrench? Using a torque wrench will ensure the wheel bolts/ nuts will come undone, even with a standard manufacturers tool. When having tyres fitted, I ask them to just "touch" the bolts down, then use my trusty Norbar.
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>>really demand accuracy
If they really demand accuracy, the fastener will have a torque plus angle specification - where it's the angle which really matters.
Edited by Number_Cruncher on 09/05/2009 at 22:56
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I got on the wrong thread but I have used a Striking wrench on occasion.
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