What's the best torque wrench?

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sansouci
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What's the best torque wrench?

Post by sansouci »

I've got an old Craftsman bending beam wrench and 3 HF (1/4, 3/8 and 1/2") spin the handle types. I've never had a digital or electronic wrench and was wondering (a) how do you test the wrench for calibration (b) are some types better than others (c) who makes the best for accuracy and durability?

--Ken
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Brucey
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Post by Brucey »

it all depends.... and it depends on lots of things.... and there is more than one way to skin a cat.

Just to give you an idea I took a trip round a local aircraft repair and overhaul facility recently. They work on civil and military stuff, and have an impeccable reputation.

They use mechanical torque wrenches. The wrench is checked at a static torque checking station, used, then checked again at the static torque checking station. If the wrench fails the second check then the job is re-done.

The checking station has two identical torque meters built into it, and it is bolted to the wall. These meters cannot be dropped, knocked, vary wildly in temperature, get oil/coffee/rainwater spilt into them, or any one of a hundred other things that tend to happen to hand-held tools. This way the day to day vagaries and changes in hand-held tools are almost eliminated as a source of inaccuracy in the torque setting procedures that are used on the aircraft.

Now you can spend a small fortune on a digital (or mechanical) torque wrench and it can come with a proper calibration cert and everything is fine... but if you drop it or knock it, what then? What if you simply leave it on the shelf for six months, and the grease in it goes a bit dry, or the spring backs off inside...?

So yes I think you ideally need a means of checking the calibration of a torque wrench. I quite recently built a dead-weight checking tool which uses various weights on a sliding beam to set the torque value. Without too much difficulty I was able to make the checker accurate to with a few percent; this turned out to be more accurate than any of my torque wrenches!

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Post by GripGreg »

Ken
Maybe go to a large diesel truck repair facility & ask questions? :-k
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Post by Da_Hose »

Ok, there is a ton of information in the world and you will need to research this for yourself to discern what is best for you.

In a nutshell.

Beam torque wrenches are wildly inaccurate in use because you have to pull on them, however in static measurement tests they are very accurate. If all you have is a beam wrench it will work fine for most things.

Depending on brand, clicker type wrenches with the spinning handle can be in excess of 10% off in the middle of their torque range and worse as you go toward either end of its limits. So a 100 lb/ft bolt could be 10 or more ft/lb too heavy or light.

Split beam torque wrenches are roughly 4% accurate in the meat of their range and are more resistant to being thrown off their adjustment than clickers. A really high quality clicker could cost more than a split beam and is about as accurate. I think a split beam is ideal for most production shop work.

Digital torque wrenches can be .05% accurate in the meat of their range and I don't recall seeing one in excess of 2%. Digital torque wrenches are for the very careful and fastidious and will last a lifetime.

I have/use a clicker for most knockaround stuff. I use my digitals for finer detail stuff like compressible gaskets or engine assembly. I also use my digital to calibrate my clicker periodically. Just use short sockets a bolt and a wide nut. My 3/8 (2 ft/lb to 50 ft/lb) is an AC Delco, my 1/2" (25 ft/lb to 175 ft/lb) is a Gearwrench. I sometimes wish I had purchased the 1/2" with a flex head though.

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sansouci
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Post by sansouci »

Brucey wrote: I was able to make the checker accurate to with a few percent; this turned out to be more accurate than any of my torque wrenches!

cheers
Now that seems like a great idea. Isn't this the mechanics of a typical sliding beam weighing scale? A known weight offset a known distance? Or am I missing some of the physics?
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Re:

Post by Brucey »

sansouci wrote: Thu Aug 13, 2015 2:43 pm
Brucey wrote: I was able to make the checker accurate to with a few percent; this turned out to be more accurate than any of my torque wrenches!

cheers
Now that seems like a great idea. Isn't this the mechanics of a typical sliding beam weighing scale? A known weight offset a known distance? Or am I missing some of the physics?
late back to this ( :shock: :shock: :shock: :oops: ) but that is exactly correct.

BTW I do wonder about electronic torque wrenches. I am sure they are wonderful when they are new but I do worry about them surviving in a typical workshop environment. I'm sure in some places workshops are warm clean and dry but in other places they are often nothing of the sort.

The basic technology of an electric torque wrench is not dissimilar to that of a digital weighing scale (a mess of strain gauges and electronics), and in terms of 'electronics in a hand tool' a set of digital Vernier calipers is probably comparable. I think that neither instrument is really good enough to survive in a typical workshop environment without there being some risk that the thing won't work right when you need it. I have taken to using only 'disposable quality' electronic verniers in my workshop, and I try to bring them indoors when I'm not using them; otherwise they don't work well when they are cold, and the slightest damp just slays them. I think that similar considerations would apply to an electronic torque wrench.

I am no big fan of clickers BTW; they are not especially accurate, and can dangerously overtorque stuff after a period of storage. But they are handy and easier to use than a typical beam type torque wrench.

FWIW the main source of error with a beam wrench is undoubtedly the bloke using it, but there is a (usually unacknowledged) secondary source of error which is simply how you hold the handle; the assumption is that you will exert a purely tangential force through the grip by hand (and with a passive wrist) but the reality is that you won't do that, not quite, and that this can make a noticeable difference to the torque measurement, because it bends the beam differently. Some models of beam wrench have tiny rounded handles to mitigate this effect, and others have a grip that is free to articulate a little instead of being bonded to the main shaft. Both help of course but can still leave you exerting a radial component of effort that must bend the beam differently and will therefore affect the calibration.

So called 'split beam' wrenches (which in essence use a short beam to flex, and then have a mechanical linkage which multiplies the small deflection into a measurement/clicker mechanism which works at low load ) almost certainly have the same problems, but they are mitigated to some extent because a) the grip is more remote from the part of the beam that actually flexes and b) the beam is very short and flexes little; this means the possible effect of a radial force component is lessened.

I suspect as in most things in life, there is no such thing as unalloyed 'perfection', only different sets of compromises that suit some better than others..... :wink:

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Re: What's the best torque wrench?

Post by sansouci »

Brucey and Jose,
Thanks for the thoughtful discussion.....

I guess the automated assembly equipment for bolt tightening is self calibrating or requires constant QC.
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Re: What's the best torque wrench?

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Re: What's the best torque wrench?

Post by Brucey »

one thing that is common to all reviews is that they cannot simulate the conditions of your use. In particular if you are an amateur spanner twirler, your torque wrench will spend lengthy periods unused. This causes clicker wrenches to dry out and once that has happened if it bad enough, you may as well take the calibration certificate and burn it. I would certainly recommend checking the calibration after any lengthy period of non-use.

BTW we don't get craftsman stuff much where I am (in the UK) but IIRC it has a good guarantee and spare parts are available. If you could get your old wrench fixed it might be a better job than a new budget quality wrench...?

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Re: What's the best torque wrench?

Post by redrumm3 »

I've been using Precision Instruments for years and have been very happy with them. They used to make the torque wrenches for Snap On, maybe they still do.

Here is the link: http://torqwrench.com/

They are available in a lot of places.

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Re: What's the best torque wrench?

Post by bpoliakoff »

Most accurate is a dial wrench
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Re: What's the best torque wrench?

Post by Brucey »

despite being sceptical of the ability for such things to survive in the rough and tumble of my cold damp workshop, I'm quite tempted by one of these

Image

or similar which converts any 1/2" drive to give a measured torque value. You can set it to give an audible alarm when the set torque is reached ( it also records the peak torque in case you overshoot), and (being small) it is easy enough to store it indoors in the warm and dry so that it doesn't suffer in the workshop.

According to the manual

https://dccf75d8gej24.cloudfront.net/do ... 215238.pdf

it should work from 0C to 40C and be accurate to +/-1%. It uses 2x CR3032 batteries. It will display in Nm, in.lb, lb-ft, and kg.m.

Potential snags are that it has batteries (that go flat, and don't like the cold) and the range of torque measurement isn't as wide as I'd like (30-360Nm). I'd quite like one with a 1/4" drive for doing really low torque stuff but I can't find one that goes down to 1Nm.

Not too expensive though; as pictured £43 inc VAT from machine mart, with comparable E-bay cheapies starting at about £33.

I can't help but think that if used with the right set of extension arms, you could turn a (say) 30-360Nm device into a 3-1000Nm device...

cheers
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