Torque wrench help

Hi everyone I'm in the process of accumulating tools for the motorbike maintenance of my pointy. In the Haynes manual the torque settings vary from minimum 11nm to max 100nm. A 10-10nm torque wrench seems really expensive what does everyone use here

[Nutsinatin]

I have a 1/4" 5-25Nm, a 3/8" 20-100Nm and a 1/2" 40-200Nm. The 1/2" gets used for rear axle nut and front sprocket nut (145Nm) and maybe a few other one off jobs. The 3/8" gets the most use and I would use it for the rear axle nut if I didn't have the 1/2" (more leverage so easier job). The 1/4" gets used mostly for spark plugs and a few other small bits.

[timwilky]

torque wrench for a spark plug!

You need to learn some feel for fasteners etc. Otherwise one day something will snap/strip

When I was a commercial fitter I only ever used a torque wrench for internal engine components. You really don't need one for axles nuts, brake callipers etc.
As timwilky says, if you rely on a torque wrench something will invariably give one day.

[millemille]

tojo82 - ignore those who say don't bother with torque wrenches and do fasteners up by feel. I've investigated enough quality lapses/incidents/accidents to know that anyone who says they don't need to use torque wrenches is talking out of their fundament. If a torque is specfied, tighten to it.

As per Nutsinatin's post - ideally you want to be using a torque wrench that's in the middle of it's operating range so a selection are needed.

Originally Posted by millemille

tojo82 - ignore those who say don't bother with torque wrenches and do fasteners up by feel. I've investigated enough quality lapses/incidents/accidents to know that anyone who says they don't need to use torque wrenches is talking out of their fundament. If a torque is specfied, tighten to it.

As per Nutsinatin's post - ideally you want to be using a torque wrench that's in the middle of it's operating range so a selection are needed.

Maybe some people do then. !
I've never had a fixing fail because of overtightening or undertightening, due to not using a torque wrench, in all my years of spannering.
You also need to remember that torque wrenches need calibrating regularly, even if you don't use them.
By all means use one but don't just keep applying pressure just because you haven't heard the click. You still need to use common sense.

[timwilky]

As I own 4 torque wrenches 1/4", 3/8" 1/2" and a feck off 1" drive giving me an across the range of 5-950NM I do think I know the place of a torque wrench.

I am by profession a Mechanical Engineer and have worked for a number of racing teams, vehicle builders, on both gas and steam turbines. So know just a little about applying fasteners. As an R&D Engineer I once undertook a study of clamping force vs torque under different conditions/steels/washer types/ thread lubrication/sealants etc. for one vehicle manufacturer.

I agree you should never use a torque wrench at either extreme of its range. Hence my over the top range of wrenches above. (Yes, I have worked on commercial, that is why I own the feck off one)

My comment about use of a torque wrench for spark plugs I think is valid. You need to seat the plug, sufficiently to seal the crush washer, over tightening will damage the washer causing a leaking seal if you are lucky, or a snapped plug/stripped head if not. This is where "feel" is the best. Perhaps as I must have fitted in excess of a 1000 spark plugs I am confident of my preferred choice.

Yes, if you are not use to it, a torque wrench is better than over doing it. But never have blind faith.

I have seen plenty of fasteners fail before they achieve the specified torque. Better to be able to sense you are at the yield point and back off, rather than continue to failure.

[ophic]

Originally Posted by timwilky

I have seen plenty of fasteners fail before they achieve the specified torque. Better to be able to sense you are at the yield point and back off, rather than continue to failure.

But if you're using feel rather than a torque wrench, you wouldn't know that it hadn't reached the specified torque.

So you're saying the best approach would be to use both?

[Craig380]

Originally Posted by ophic

But if you're using feel rather than a torque wrench, you wouldn't know that it hadn't reached the specified torque.

So you're saying the best approach would be to use both?

When using a torque wrench you can still feel the resistance as the nut / bolt tightens. When doing things like cylinder head nuts etc I usually do all the nuts finger-tight first (using my fingers to grip the socket), then torque to half the specified setting, then torque up to the target figure.

As an experiment I recently checked the calibration on my cheapo Draper micrometer torque wrench, which I'd never done before. It was over-reading by 10% (i.e. 20lb-ft on the scale was a true 18lb-ft). So now I'm using it loads more

[embee]

I agree with timwilky. I have over 35yrs in automotive design/development, and fastener load is a major topic, it's what holds the world together.


A big point to be aware of is that very often the torque figures given are for dry (or essentially dry) assembly. In the big wide world we all put some sort of lubricant on threads. As a rough guide I usually allow about 10% reduction for an oiled/greased thread.


Use a torque wrench intelligently, don't just set it and go for it. If in doubt, work up towards the value in steps and be prepared to stop early. I find caliper mounting bolts with fine threads in alum are rather touchy, I always err on the side of caution.


Most critical fasteners in automotive use are now tightened to yield using electronic sensing systems (SDS etc), it monitors the torque and angle and detects when the fastener starts to yield, i.e. the torque doesn't increase as the angle increases. This is in fact a very useful method since the clamping load can be engineered very precisely using the yield characteristics of the material and the cross sections. You can usually do this 2 or 3 times to a fastener, it's not usually necessary to replace even these critical fasteners every time providing you stop tightening at the right time.


Out in the real world we don't all have these systems in out tool boxes, so torque it is.


Best advice I can offer is to get hold of a few nuts&bolts and tighten them until they fail, then you get the "feel" for how they yield. When you feel that in a real situation, stop tightening.


Spark plugs are an odd case, the washers are designed to yield (to conform and thus seal), and it can be tricky to differentiate between the washer crushing and the thread yielding. Experience is what you get just after you needed it.