Talk to me about torque wrenches...
Discussion
A cheap torque wrench will be fine... no need for a Teng or Halfords Pro.
Draper beam-type torque wrenches are on eBay for £11.50 delivered, or a cheap micrometer (click type) torque wrench is £18.
I've got a cheap micrometer torque wrench I use for wheel nuts, etc and a Halfords Pro for engine work. The cheap torque wrenches are, in my experience, just as accurate as the branded stuff... certainly accurate enough for non-critical stuff like wheel nuts and the like. I've actually baselined the accuracy of a couple of bargain basement torque wrenches against a freshly calibrated Teng wrench and there was no notable difference between them.
For engine work, where accurate torque is critical, I prefer the psychological comfort of using a decent torque wrench like the Halfords Pro
If you get a micrometer torque wrench, make sure you store it properly (torque set at minimum) and don't drop it or use it for tightening stuff. Use it only for what it's designed... setting final torque.
Draper beam-type torque wrenches are on eBay for £11.50 delivered, or a cheap micrometer (click type) torque wrench is £18.
I've got a cheap micrometer torque wrench I use for wheel nuts, etc and a Halfords Pro for engine work. The cheap torque wrenches are, in my experience, just as accurate as the branded stuff... certainly accurate enough for non-critical stuff like wheel nuts and the like. I've actually baselined the accuracy of a couple of bargain basement torque wrenches against a freshly calibrated Teng wrench and there was no notable difference between them.
For engine work, where accurate torque is critical, I prefer the psychological comfort of using a decent torque wrench like the Halfords Pro
If you get a micrometer torque wrench, make sure you store it properly (torque set at minimum) and don't drop it or use it for tightening stuff. Use it only for what it's designed... setting final torque.
Edited by ian_uk1975 on Saturday 6th April 11:41
my neighbour purchased a small draper torque wrench for use on his bike. He did an oil change then decided to torque up the sump plug and sheared it clean off, we found out by putting it in the vice that it was way out of calibration.
Not saying every wrench is like this but just a warning.
Not saying every wrench is like this but just a warning.
Yes.
Set the wrench to say 50Nm.
Grip the square in a vice with the handle horizontal.
Hang an watertight bag off the handle.
Fill the bag until the the wrench clicks.
Measure the volume of water.
Do the maths.
e.g. you have 17lt of water which is 17kg or 166.7 Newtons force acting on the lever.
the distance from the drive square to the point where the bag was suspended is 30cm.
100/30=3.3333
166.7/3.3333=50Nm
HTH
Steve
Set the wrench to say 50Nm.
Grip the square in a vice with the handle horizontal.
Hang an watertight bag off the handle.
Fill the bag until the the wrench clicks.
Measure the volume of water.
Do the maths.
e.g. you have 17lt of water which is 17kg or 166.7 Newtons force acting on the lever.
the distance from the drive square to the point where the bag was suspended is 30cm.
100/30=3.3333
166.7/3.3333=50Nm
HTH
Steve
stevesingo said:
Yes.
Set the wrench to say 50Nm.
Grip the square in a vice with the handle horizontal.
Hang an watertight bag off the handle.
Fill the bag until the the wrench clicks.
Measure the volume of water.
Do the maths.
e.g. you have 17lt of water which is 17kg or 166.7 Newtons force acting on the lever.
the distance from the drive square to the point where the bag was suspended is 30cm.
100/30=3.3333
166.7/3.3333=50Nm
HTH
Steve
Neat, I will try that. Thanks. Set the wrench to say 50Nm.
Grip the square in a vice with the handle horizontal.
Hang an watertight bag off the handle.
Fill the bag until the the wrench clicks.
Measure the volume of water.
Do the maths.
e.g. you have 17lt of water which is 17kg or 166.7 Newtons force acting on the lever.
the distance from the drive square to the point where the bag was suspended is 30cm.
100/30=3.3333
166.7/3.3333=50Nm
HTH
Steve
eltax91 said:
Slight thread hijack. Is there an easy way to test my click type torque wrench to check how accurate it is?
Couple of years ago I had my 10/15 year old click type torque wrench tested and re-calibrated by my local tyre company - http://www.bushtyres.co.uk/They charged £10 to test and £10 to re-calibrate - paperwork and a re-test date sticker included!
As has been said always zero it after use and only use for torquing not as a breaker bar.
Just remember that it really isn't the perceived accuracy of the tool itself. Rather it's the sensible application of lubrication of the threaded components.
Torquing is all about applying a clamping force by stretching the threads of the fastener to the optimum tensile strength whilst employing the greatest clamping force using the least effort.
Generally, dry threads will require far higher torque figures to achieve the same clamping force as against a lubricated thread, washer, nut, base lubrication.
Depending on the coefficient of lubrication it is possible that a variation of 60% of clamping force can be found from "dry" to something like Copper Disulphide coatings.
Basically, never, ever "torque up "a dry fitting.
Obviously what you need to look for in any torque wrench is the abilty to repeatedly replicate the set figure within +/- .5%
Torquing is all about applying a clamping force by stretching the threads of the fastener to the optimum tensile strength whilst employing the greatest clamping force using the least effort.
Generally, dry threads will require far higher torque figures to achieve the same clamping force as against a lubricated thread, washer, nut, base lubrication.
Depending on the coefficient of lubrication it is possible that a variation of 60% of clamping force can be found from "dry" to something like Copper Disulphide coatings.
Basically, never, ever "torque up "a dry fitting.
Obviously what you need to look for in any torque wrench is the abilty to repeatedly replicate the set figure within +/- .5%
ND, isn't the point of torquing that you achieve the clamping pressure you want rather than achieving max-clamp force?
And I recall reading a poster on here saying that if you copper-slip a fixing then you need to tighten more than the specified torque.
Maybe I am misinterpreting things so I am happy to be corrected.
And I recall reading a poster on here saying that if you copper-slip a fixing then you need to tighten more than the specified torque.
Maybe I am misinterpreting things so I am happy to be corrected.
The Black Flash said:
Pretty sure that's not right. Torque settings are for dry fasteners, unless specified otherwise (i.e. it says "oil the threads then torque to xxx") AFAIK.
Competent engineering practice NEVER recommends running dry threads. Even engine oil on the threads will reduce the force required by at least 20% to achieve the same clamping force. Think about it, mass produced threaded fasteners cannot in any way reproduce a torque value within +/- 10% due to manufacturing tolerances. Apart from the nut / stud threading discrepancies ( some nuts you can spin freely all the way down the thread, some nuts may stick requiring more effort) you need to examine the landing effort.Here, if you take the example of torquing a cylinder head bolt on an aluminium head, without any lubrication between the underside of the washer you can gouge the washer into the aluminium head without achieving the neccessary clamping force, but, yet achieving the given torque figure.
Manufacturers are very casual about these figures and more thought needs to be given about this important issue. Although, again, "repeatability" is the key. Whatever value is used then the torque wrench needs to be capable of achieving this value to within 2 1/2% of repeatibility
niccis dad said:
Manufacturers are very casual about these figures and more thought needs to be given about this important issue.
Whenever you read a repair manual (even engine rebuild manuals), you'll see statements like 'torque bolt x to xx lbft'. There is almost never any instruction given on what should (or shouldn't) be applied to the threads to achieve the target clamping force at the fastener. Even in rare cases where an instruction is given (for example, use engine oil on the threads), the instruction is often vague (what viscosity of engine oil, etc). The only statement I've personally seen that has been sufficiently specific and clear was from the ARP instructions I followed when installing head stud nuts... they have a specific moly lube to use.All this makes me think there is a call for a standardised thread lubricant to be used whenever specifying torque values. This could either be a specific weight of engine oil, or a specialist lube sold specifically for the purpose. Wonder why this isn't the case already?
PS. Thread burnishing is another issue that can affect clamping force... with some fasteners, it is necessary to 'cycle' the fastener before torquing it to the specified value, presumably in order to reduce the friction coefficient of new threads to a nominal value.
Torque values are for dry threads, especially standard torque values. There are also guidelines for how to adjust the value if there is a lubricant used. Where lubricants are used in practice the engineer will allow for this and on there drawing they will specify the lubricant and torque value, to be used.
For the home mechanic this may in the service manual or not available. One must make a educated decision on what torque/lubricant to use.
For the home mechanic this may in the service manual or not available. One must make a educated decision on what torque/lubricant to use.
On car manufacturing lines, the fasteners are not lubricated. What the manufacturers do is specify a fastener to give the correct clamping force or preload when stressed to 70-80% of the fastener yeild strength. The torque of the dry fastener is determined to give the required preload; this can be calculated by T=K*D*P where T is torque, K (see footnote) in the nut friction value, D is the nominal fastener diameter and P is the prelead required.
Lubricating threads where the torque specified is determined from a dry value can result in ofer tensioning the fastener. So if you want to lubricate your fasteners, go right ahead, but ensure you have done the maths as to what the new torque value should be after lubrication.
The K value is a constant in the above formula and it in it's self is determined by
K= (1/d) x [0,159*P + 0,578*d_2*Mue_G) + (D_Km/2)*Mue_K]
d: nominal diameter of the bolt, P: Thread Pitch , d_2: Pitch diameter D_Km: Mean bearing diameter / underhead Mue_G: Thread friction coefficient
Mue_K: Underhead friction coefficient
Lukily, most K values have been calculated and tables are available.
Lubricating threads where the torque specified is determined from a dry value can result in ofer tensioning the fastener. So if you want to lubricate your fasteners, go right ahead, but ensure you have done the maths as to what the new torque value should be after lubrication.
The K value is a constant in the above formula and it in it's self is determined by
K= (1/d) x [0,159*P + 0,578*d_2*Mue_G) + (D_Km/2)*Mue_K]
d: nominal diameter of the bolt, P: Thread Pitch , d_2: Pitch diameter D_Km: Mean bearing diameter / underhead Mue_G: Thread friction coefficient
Mue_K: Underhead friction coefficient
Lukily, most K values have been calculated and tables are available.
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