Eric is exactly right.

Torque wrench smork wrench. What kind of accuracy do you think you are
gaining?

I'm not a certified bike mechanic but I do have over 20 years experience as
a mechanical engineer specializing in tool design.

Here is what a leading screw manufacture says:

Torque wrench +/- 25% accuracy
By feel +/- 35% accuracy

I can send you their documentation if you want it. In fact, I have not
found a recent manufactures publication that lists torque ratings. I have
some old documents that list off a number of requirements that must be met.
The most import is that it must be an unused screw with lubrication from the
factory.

-----Original Message-----
From: obra-bounces@list.obra.org [mailto:obra-bounces@list.obra.org] On
Behalf Of Eric Chu
Sent: Wednesday, July 23, 2008 1:03 PM
To: OBRA chat
Subject: Re: [OBRA Chat] Tool envy: torque wrench vs. experienced mechanic

Sure, a tool is just a tool. And component quality, surfaces and bolt prep
all affect the tension on the threads. The question, in my book, is whether
you are doing the best you can with the tools that are available?

No matter how experienced a mechanic is, torqueing fasteners to very
specific range consistently is a real challenge, especially with all the
fussy components that are on the market now.

If you took a four-bolt stem faceplate and tightened all the bolts by hand,
and then checked them with a decent torque wrench, I think you'd be
surprised at how different the tightness was from one another.

Ultimately, I think the bottom line is customer satisfaction and trust. and
unfortuanately, especially for a retail business, liability protection.
Having a reliable tool that is calibrated an established standard is waaaaay
better than saying, "it felt just right" so I don't know why the carbon stem
failed.

so..the best scenario? an experienced mechanic AND a torque wrench.

eric
------------
bikemecca.com

--------------------
Message: 3
Date: Tue, 22 Jul 2008 13:56:07 -0700 (PDT)
From: john
Subject: Re: [OBRA Chat] Tool envy: Effetto Mariposa Giustaforza
Torque Wrench

>>>>>The main issue: When torque is applied to a bolt, most of that torque
(90-95%) goes
into overcoming friction, only 5-10 % go into preload. That means if the
friction
is off a little, maybe a little galling / burr,? or maybe slippery coating,
etc,
the pre-load can be off? whole lot (personal testing, off easily by half to
double
! ).? Its actually been shown that a experienced machinist / mechanic with
just
a normal wrench can be just as accurate. <<<<
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