Only 5Nm on a stem/handlebar clamp?

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Cugel
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Cugel » 14 Nov 2019, 10:04am

Mick F wrote:I never give it a second thought.
(snip)


No, indeed to goodness; you don't. :-) How many "its" would you see differently if you did?

Cugel in Ceredigion.

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Mick F
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Mick F » 14 Nov 2019, 10:23am

Of all my years of working on stuff, I've developed a knack I suppose.

Torque wenches I've used in my whole technical life include the steel bolts in delicate aluminium units, and working on cars........ head gasket bolts and big ends+journals and the odd wheel bearing or two.

I have a torque wrench, last used on a Mini cylinder head and that must be 15years ago or more.
I once tried it to set the fixing ring on a Campag cassette to the correct torque, but as the ring is serrated, it clicks as it tightens and it upset the torque wrench clicking ......... so I gave that up as a bad job.
Mick F. Cornwall

Cyril Haearn
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Location: Between the woods and the water

Re: Only 5Nm on a stem/handlebar clamp?

Postby Cyril Haearn » 14 Nov 2019, 10:31am

In another life you could have maintained diesel-hydraulic locomotives at Laira

'I can't torque, I have lost my Voith', bleated Western Thunderer as she limped into the depot :?
Nice one Cyrille, nice one son..
Cycling-of course, but it is far better on 49" fixed
We love safety cameras, we love life "1330"

slowster
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Re: Only 5Nm on a stem/handlebar clamp?

Postby slowster » 14 Nov 2019, 10:35am

BITD of quill stems, short handled L allen keys were the norm, and I can remember a half joking comment that the rule of thumb for tightness was to do the bolt up until the end of the handle made a red mark in the palm of your hand, and I cannot recall needing a key smaller than 4mm.

With regard to the quill stem design being stronger or more tolerant of excessive torque etc. than ahead stems, I'm not sure it's completely black and white. When Cinelli started to make quill stems and 26mm bars again recently to capitalise on the market for retro products, it had to increase the strength of the old designs to meet the current EN standards, i.e. the old design would have failed. Moreover, it only chose to make the 1R stem, not the 1A stem that MickF has, and I suspect that the 1A design was a case of form over function which could not be made to provide an adequate level of safety and reliability, unlike the simpler 1R design.

Neverthless I do think it's generally true that the quill design and older equipment was much more tolerant of over torquing. If you had a fall on a bike with a quill stem, the quill would often be twisted in the steerer by the impact of the bars against the ground. The result was that the bars were often undamaged and the stem could usually simply be brought back into alignment by grasping the bars and twisting them in the steerer. That's less likely to happen with the much larger clamping surface of an ahead stem around a 1 1/8" steerer, with the result that in a similar fall it's probably more likely that something will be destroyed by bending or completely breaking.

Interestingly Thomson switched to using 3mm allen head bolts instead of 4mm on its ahead stems because too many people over tightened the bolts, which probably reflects the fact that there are just as many ham-fisted users nowadays as in the past, and a lot of them either don't have, won't use or can't afford a torque wrench.

pwa
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Re: Only 5Nm on a stem/handlebar clamp?

Postby pwa » 14 Nov 2019, 11:13am

Just as an example of the inexpensive torque devices out there:

https://www.sjscycles.co.uk/tools/topea ... cket-5-nm/

I don't expect this is all that accurate and I won't be buying it, but if I were riding a bike put together by somebody else I would rather they had used this than an allen key on its own. At least then there is some hope of a buffer between an overenthusiastic tightener and a fragile component on which my wellbeing depends.

fastpedaller
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Re: Only 5Nm on a stem/handlebar clamp?

Postby fastpedaller » 14 Nov 2019, 11:47am

Slowster, did you get your Cinelli 1A and 1R muddled? ISTR the 1R is the wedge type (form over function) model.
The difficulty with using a torque wrench is knowing what conditions are required as far as the thread is concerned, i.e. Is thread dry (is that completely dry and devoid of any manufacturing 'oil' and therefore needs cleaning with alcohol? Or is thread greased (or indeed need anti-sieze or Loctite)? The difference between the 'thread preparation' can make a large difference to the torque needed, and is more apparent at low levels of torque.

slowster
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Joined: 7 Jul 2017, 10:37am

Re: Only 5Nm on a stem/handlebar clamp?

Postby slowster » 14 Nov 2019, 1:29pm

fastpedaller wrote:Slowster, did you get your Cinelli 1A and 1R muddled? ISTR the 1R is the wedge type (form over function) model.

:oops: You're quite right, I mixed them up.

Manc33
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Manc33 » 14 Nov 2019, 1:56pm

So are the first few people posting after me suggesting that if you clamp 4 bolts at 5Nm each, that's only putting 5Nm of total force on the part? If that were the case your handlebars would be slipping all the time and they don't, at least not on metal ones.

For anyone worried about overdoing it on carbon parts, just invest in one of these, I held off for ages because they are pricey for what they are, but it's easily my most used tool now. They are available at just about every big bike shop.

Ritchey Torque Key

Image
When two cyclists get married, they should throw anodized cable crimps instead of confetti.

Brucey
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Brucey » 14 Nov 2019, 2:01pm

Manc33 wrote:So are the first few people posting after me suggesting that if you clamp 4 bolts at 5Nm each, that's only putting 5Nm of total force on the part? ….


Anything in Nm is a torque not a 'total force'.

If in doubt, read the instructions; there may be a list of compatible/approved stems.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

DNC123

Re: Only 5Nm on a stem/handlebar clamp?

Postby DNC123 » 14 Nov 2019, 2:06pm

An engineer told me before he died...
(Hands up if you know the rest of that pub outing song!!!)
...that an allen key would tighten to the correct torque for the size of bolt being tightened if it was done up hand tight, firmly but without using undue force. Something to do with the diameter of the head and the length of the key. Obviously he was talking about "proper" workshop keys, not the cut down version carried by cyclists. No need to lean on the key or use an extender bar.

Manc33
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Joined: 25 Apr 2015, 9:37pm

Re: Only 5Nm on a stem/handlebar clamp?

Postby Manc33 » 14 Nov 2019, 2:17pm

When I got a 5Nm torque key I realised 5Nm was more than I thought.

If you have 4 bolts at 5Nm each it has to be a total force of 20Nm.

Just like if you put a 10lb weight on some scales than added another 10lb weight. It doesn't stay at 10lb because you're spreading the weights apart or whatever. I still don't know what that China handlebar means when it says 5Nm, because 5Nm isn't enough to hold a handlebar on a stem.

I use bar ends so that's what stops me getting them, although you can apparently get bung things to stop the carbon compressing, what's the point when they cost more than the handlebar. It's not saving much weight either, once those metal bungs are added you're just getting back to the weight of a metal handlebar. :!:
When two cyclists get married, they should throw anodized cable crimps instead of confetti.

tim-b
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Re: Only 5Nm on a stem/handlebar clamp?

Postby tim-b » 14 Nov 2019, 5:00pm

Hi
When I got a 5Nm torque key I realised 5Nm was more than I thought.

5Nm is a maximum, not a target. If the various components are secure at a lower torque then happy days

Torque is a measurement of the twisting force at each bolt, not the linear clamping force

The steerer bung has two functions:
It's necessary to pre-load the headset bearings before securing the assembly with the handlebar stem
It provides a degree of support to the steerer tube

Regards
tim-b
~~~~¯\(ツ)/¯~~~~

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Only 5Nm on a stem/handlebar clamp?

Postby Brucey » 14 Nov 2019, 6:23pm

Manc33 wrote:
If you have 4 bolts at 5Nm each it has to be a total force of 20Nm


No: as per my previous post Nm is torque (not force), so adding torque values from several bolts does not make a 'total force'.

What the torque is intended to produce is a certain tension in each bolt, and you can sum these tension values in various ways (for all the good it will do you).

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Samuel D
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Samuel D » 14 Nov 2019, 11:13pm

I recall trying to explain this a while ago. Where did this persistent notion of torque as clamping force come from, Manc33?

As for the Chinese bar with the 5 Nm symbol, the number was probably pulled out of thin air or copied from a brand name’s installation instructions. Still, it’s probably about right.

richardfm
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Re: Only 5Nm on a stem/handlebar clamp?

Postby richardfm » 14 Nov 2019, 11:44pm

CX-3 wrote:An engineer told me before he died...
(Hands up if you know the rest of that pub outing song!!!)
...that an allen key would tighten to the correct torque for the size of bolt being tightened if it was done up hand tight, firmly but without using undue force. Something to do with the diameter of the head and the length of the key. Obviously he was talking about "proper" workshop keys, not the cut down version carried by cyclists. No need to lean on the key or use an extender bar.

An Engineer Told Me is one of the songs we used to sing at sea when I was in the merch many years ago. That was also where I learnt that if you use the correct spanner or allen key then hand tight firm is right. I've only ever used torque wrench for cylinder head bolts and wheel nuts/bolts on cars and caravans