| Subject: | Re: Tool envy: torque wrench vs. experienced mechanic |
| Date: | 07/24/2008 12:24 AM |
| From: | john <twotiretinker-obr..@yahoo.com> |
|
well the way i wrote it, i left it kind of open.. and never said that wasn't a nice torque wrench... and it is specifically made for bicycles,... i wouldn't see accuracy as the main advantage, but the other features, as you pointed out. Mainly wanted to add, to be aware, that the end result wanted is bolt tension, not torque. and this being a large function of friction, which can vary, depending.. In the case of most 5 mm / 6 mm bolts.. the bolts are pretty standard, the bolt threads are hard chrome or something, the other threads are aluminum, and the guys that come up with the torque values hopefully tested it (they probably torqued to strip then halved or something like that..) so a known situation.. so anyway the end result in this particular situation is probably fairly accurate. so just wanted to raise awareness... Its hard to write this stuff and cover all bases, all situations.. words like "sometimes", "probably" and "might", "maybe" and "can-be", "in my opinion"get heavily used. and seriously, large books have been written on this subject. In most bolting situations (non bicycle), Its pretty simple: you tighten the shit out of them. Almost to where they bust. Most good machinists/mechanics can feel when the bolt starts stretching (ie yielding) and that's where they stop. This is good and thats good bolted joint. But of course the clamped components need to be accounted for too! One aspect of good design is typically such that a bolt can be broken before clamped components are warped or stripped or in some other way damaged (in my opinion). But of course not all design can consider only that factor, and not everyone has the time or the money to do perfect design, and most of the time it probably just doesn't matter and who the hell cares, kind of like all this stuff i am writing. Now, this bicycle stuff, especially it appears with this new lightweight stuff, as I am only now realizing / learning about, is quite the opposite in that the bolts are often stronger then the components... Too much torque and you strip threads, crack carbon, etc. And then there are things on a bicycle where threads (pedals, bottom bracket) are used that really aren't used in a manner to hold a preload. they are still a holdover from before bolted joints were understood. (bolted joints really weren't widely used ("understood") and thus specified in design of say a bridge until 1950's or so.. i think the Mackinaw bridge in michigan was one of the first big structures to use bolts rather than rivets. (Obviously the physics was probably understood decades before). One reason I suppose was that the bolts weren't mass produced until until they figured out how to roll the threads. Prior to that the threads were cut on a "screw-cutting lathe", much more expensive and not near as strong. Its amazing how much we take them for granted, and few of us realize how much work it took and takes to make those damn little things with the accuracy that they have. Anyway yes you are right, if someone drops $200 plus or whatever on carbon handlebar / stem or etc.., I sure as hell will be using the torque wrench too. but first i would try to hand it to hand it off to you. --- On Wed, 7/23/08, Eric Chu wrote:
I think you meant the other guy is right. although I think we're both right to some extent. a lot of things
Having been in retail as a certified tech and having worked for
For the record, the Effetto Mariposa wrench has a stated accuracy of
If a leading screw manufacturer says torque wrench's only have +/-
(and I have not been hired to flog this product) eric
> Eric is exactly right.
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