LBS and Torque Wrench

[Profpointy]

Good point, I should have expounded. Whenever there is a single bolt in a stem, it is usually a 6mm bolt and over torquing it is less critical than over torquing bolts in pairs or double pairs, because the latter are invariably much smaller, with 4mm diameters. The larger the bolt, the less critical its torque becomes (wrt to the bolt, not the device it is clamping) because the margin of error is so much larger.

Even this may not be so obvious, but the area of a 6mm bolt is 114 mm2 whereas the area of a 4mm bolt is 50mm2. That 2mm makes a huge difference. Strength is analogous to area.

On some stems, there are 4 x 4mm aluminium bolts. Those are super critical.

Can I ask what you mean by area in the numbers above ?

 

[Yellow Saddle]

Can I ask what you mean by area in the numbers above ?

The area calculated from the diameter of the bolt.

 

[Profpointy]

The area calculated from the diameter of the bolt.

I wondered if it was sonething more complicated but if not, I think your numbers are a bit out. It was pi r^2 when I was at school.4

 

[Yellow Saddle]

Duh! Thanks for pointing out, I'll fix it.

Edit: Now fixed.

 

[minininjarob]

So you would advocate reusing cylinder head bolts when the manual says not to due to them stretching

Cylinder head bolts are specifically designed stretch bolts which are single use only and must be torqued up very accurately in a set pattern, completely different to normal bolts used in cycling.

 

[minininjarob]

If you are earning a living mending bikes, then the comment that you know what a certain torque feels like wouldn’t stand up in court in the event of a failure that caused an injury, anyone that is in this line of work needs to cover their back.

That wouldn't really work either, as if the prosecution went that far they would just go further and ask when the torque wrench was calibrated, what the calibration schedule was, was the wrench ever dropped, how was it stored, what engineering training did you have in the use of TR's, did you ask the manufacturer what specification of lubricant should be used (if at all) when assembling the component to the advised torque.....

 

[PhilDawson8270]

That wouldn't really work either, as if the prosecution went that far they would just go further and ask when the torque wrench was calibrated, what the calibration schedule was, was the wrench ever dropped, how was it stored, what engineering training did you have in the use of TR's, did you ask the manufacturer what specification of lubricant should be used (if at all) when assembling the component to the advised torque.....

This is when it does get serious.

I got involved in some off shore oil rig pipeline system design, as a Mechanical Design Engineer. Every bolted joint required a joint certificate, and every certificate contained the following:

Torque Wrench Make and Model
Torque Wrench Serial Number
Torque Wrench Calibration Date
Torque Wrench Calibration Certificate Number
Joint size and rating
Type of gasket used
Bolt size and length
Nut size
Bolt material
Nut material
Bolt coating
Nut coating
Lubrication used (Manufacturer and Product)
Coefficient of friction
Tightening sequence of bolts
Each torque stage
final tightening torque
Residual bolt stress (clamping force)

As you say, somebody simply saying they use a Torque Wrench ain't gonna stand up when the stuff hits a fan.

 

[Nigelnightmare]

That may well be the case, but both of mine have a reverse rotation switch, presumably for some purpose. Both have 3 point hand-written calibration certificates too, but I don't suppose that's going to convince the "finger-in-the wind-experienced-old-timer" lobby.

Left hand thread!

 

[DRM]

That wouldn't really work either, as if the prosecution went that far they would just go further and ask when the torque wrench was calibrated, what the calibration schedule was, was the wrench ever dropped, how was it stored, what engineering training did you have in the use of TR's, did you ask the manufacturer what specification of lubricant should be used (if at all) when assembling the component to the advised torque.....

Not really, once the HSE get involved, you are in deep bother, unless you show that you reasonably took the correct actions, anyone wanting to do engineering work for a living has to cover their back by getting it right every time, nipping a fixing up by hand does not cut it where a manufacturer specifies a torque range & if or what lubricant/threadlock is required, it goes without saying that torque wrenches need to be calibrated at the recommended intervals too, as well as keeping a record of calibration too, as well as to be stored correctly with the wrench not set to any torque.

 

[DRM]

Cylinder head bolts are specifically designed stretch bolts which are single use only and must be torqued up very accurately in a set pattern, completely different to normal bolts used in cycling.

The original comment was that used bolts are ok to use, I put that as an example that not all bolts can be reused safely, I know how to do a cylinder head gasket thanks.

 

[subaqua]

Unfortunately the torque wrenches and torque values that are bandied round the cycling world nowadays I think are just a way of manufacturers getting out of warranty claims. The torque wrenches sold to the cycling public are cheap things, inaccurate and are nothing like the sort of torque wrench you'll see a decent engineer using. My father was an industrial engineer all his life and laughed at torque values for bike stuff. Correct torque depends on so much, the type of fastening, the lubrication, the type of metal used, the thread pitch. ALso the TR's need calibrating, you can't drop them or they go out of calibration. So picking up your £30 TR and tightening to 10Nm means absolutely nothing.
Much better to have a good feel for components and your tools. A good rule is that your controls only need tightening until they don't slip in normal use.
In the OP if the mechanic tightened the post just enough to stop it moving when you were riding it then it was perfect. In that way if you crash things are likely to move rather than snap or bend. Seatposts/brake lever/gear levers/stem can all be treated this way.
I am so thankful my father taught me how to use tools properly. Yes I broke stuff when I was a kid but I was an idiot.
All you need are quality tools and an understanding and sympathy of how mechanical things work.

Oh, and a Park workstand, I should have bought one of those 20 years ago.

Surprisingly enough some of the torque wrenches we use in work are “ cheap ones sold to the public” and they tend to stay accurate longer than the horrendously expensive ones wheeled out for client witness testing.

Dropping them doesn’t automatically put them out of calibration. Based on years of engineering in practice.

That said if you look after stuff it won’t break as quickly.

I can tighten crush terminals on MCB to manufacturers torque without my Torque driver . The @Sea of vapours test proved that when a client rep with more letters after his name than in it, but with no practical experience pulled me on it once. The look on his face was priceless.

Wet and dry torque values are different . If you loctite a thread then it can act as a lubricant so it may not be as tight as you think.

Finally the torque setting isn’t for the bolt it is for what’s being clamped by it. Copper busbars have a higher torque setting than aluminium busbars as the Aluminium is softer and gets squeezed out easier

 

[subaqua]

That may well be the case, but both of mine have a reverse rotation switch, presumably for some purpose. Both have 3 point hand-written calibration certificates too, but I don't suppose that's going to convince the "finger-in-the wind-experienced-old-timer" lobby.

Left hand threads ...

 

[randynewmanscat]

I made a light-hearted joke with him about it and he says he never uses one and knows exactly what 4Nm feels like.

😂

 

[weareHKR]

I once asked the guy in our local Halfords to tighten up the stem bolts on a bike I was collecting for a friend.
When he emerged with an Allen key, I suggested he should use a torque wrench... "naaa, no point mate, the lads just use them as a ratchet" 😲 ....

 

[Ian H]

As mentioned somewhere above, the correct torque for a seatpost clamp bolt is just enough to stop it slipping in use. That'll be rather less than the maximum, unless you have the wrong diameter post.