Two Torque Questions
 

Question 1: Here's what my torque wrench looks like at rest:

http://bikeforums.net/attachment.php...hmentid=318609

You can see that it's not zeroed out. From my Intergoogling, it looks like I can calibrate/fix it by simply bending the pointer beam until it is at zero. Correct?

Question 2: Here's the torque info on a stem:

http://bikeforums.net/attachment.php...hmentid=318610

I think it says "TORQUE: 40 ln-lbf [4.5n-m]"

Am I correct that this means I should use my torque wrench, and apply pressure until the (newly calibrated) needle points to 40 FOOT-POUNDS?

Thanks!

Im guessing the "TORQUE: 40 ln-lbf [4.5n-m]" is referencing the 2 fasteners its pointing to.

Yes
No. It's INCH pounds. 12 Inch-lb. = 1 foot-lb.

That's interesting. But what's the "f" for?? It seems to say "40 ln-lbf" or is that some other character?

lbf might mean lbs-Force. Underwater, bouyancy may change the effects of gravity. lbf denotes force equivalent applied perpendicular to the moment arm regardless of gravitational or other considerations.

It's supposed to be "in-lbf". Inch pounds force.

Just to be sure, we can convert the number in newton meters since it's pretty clear. 4.5 n-m is equivalent to approximately 3.3 foot pounds or 38.3 inch pounds.

The "f"stands for force. The "f" isn't necessary since "pound" is a measure of force already. I suspect it's sort of a retronym because the maker is used to the metric system, where kg. is a unit of mass, so they use kgf as a unit of force. Not thinking, the maker probably added the f here too.

On the beam type wrench, hold the driver in a vise with the beam horizontal, then gently bend the needle arm back to zero.

After you zero the indicator needle, it's usually a good idea to check the calibration.

http://i42.photobucket.com/albums/e3...ps40a732ff.jpg

1. Clamp square-drive in vise with wrench-arm perfectly horizontal, might need to use some V-blocks if your wrench's square-drive is 45-degrees off
2. using a strong rope/cable, hang a weight of around 25% of wrench's max capacity from handle (use precision scale to measure this weight, such as calibrated scale at the Post Office or UPS office. Bathroom scale isn't accurate enough).
3. length = measure distance from centre of square-drive to hanging-cable in inches
4. calculated torque = weight * (length /12)
5. read off torque indicated by wrench, how closely does it match calculated torque value in previous step?

Check this Park Tool - Torque specifications page for a list of common torque-settings on bikes. The highest torque you'll typically use is around 30 lb*ft for the crankarm-bolts and cassette-lockring.

Your wrench is way too big and inaccurate for the ranges used on bikes. Heck, it's a bit much for cars unless you regularly install cylinder-heads. You may want to get something in the 0-400 in*lb range (0-33 lb*ft) to work on bikes with higher resolution and accuracy.

OK, I've got it now, thanks. You guys are great!

I'm going to buy a new torque wrench. Any recommendations on a good all-purpose one?

There is no one "all-purpose" torque wrench for bike use. You really need two; a low torque 1/4" square drive (typically 0-60 in-lb, 0- 7 N-m range) and a higher range 1/2"-square drive (typically 0-150 Ft-lb, 0-100 N-m) The first is used for things like handlebar and stem clamps and the second for bottom brackets and crank bolts.

I'm partial to beam type torque wrenches. They are less expensive and more rugged and can be "recalibrated" as FBinNY described by bending the pointer back to zero if needed. "Clicker" wrenches have a big advantage if you are working on bolts where you can't easily see the wrench, such as automobile applications, but that never applies to bikes. Sears Craftsman line and Park Tools both sell good quality beam wrenches and even Harbor Freight has adequate ones.

I'm guessing that if it doesn't match closely enough, you discard the wrench (or adjust the measurements in your head).

Right -- I'll get a 0-60 in-lb beam model.

Why would you discard a perfectly good torque wrench? Since the working part is the beam itself and not the needle which is simply a fixed reference, moving the needle has absolutely zero effect on the accuracy of the tool. And the beam itself won't ever change since the flex property (Young's Modulus) is unchangeable.

Reset the needle to zero, and it'll be fine for everything short of moon rocket work. Certainly it'll be more than adequate for bike use.

Dan was suggesting checking the calibration after resetting the needle to zero. As you say, the flex property is unlikely to change.

I was just making the point that if that calibration failed, there was no way to adjust it.

True, but OTOH, flex beam engineering is very straightforward and makers generally hit the target, or come very close. If you opt to recalibrate be aware that the exact location within the 4-5" handle area will affect the calibration.

In any case you're working on a bicycle, not a rocket ship, and there has to be a tolerance for torque values because fastener friction varies tremendously. Even if it seems to be off a bit, your torque wrench will still be far more accurate than necessary for the task at hand.

Yes. Beam wrenches have handles mounted on a pivot. When setting torque, the handle should be held so that it is putting force only through the pivot, being free on the pivot and not contacting the wrench on either end.

That is correct. Pound and Kilogram are measures of mass. Pound-force and Newton are the equivalent measures of force, e.g. the force exerted on a scale by each mass at one g (standard gravity = approx. 32.2 ft/sec^2 or approx. 9.8 m/s^2)

Dan's illustration and procedure apply to "clicker" type torque wrenches which can come out of calibration and have no pointer to indicate they have. These can be "rezeroed" with an internal adjustment if you know the error. Torque wrenches used in industrial applications are usually clicker or dial or electronic types and are frequently recalibrated for critical applications.

While the kilogram is a unit of mass, the pound is not the English system unit of mass. The traditional English unit of mass is the poundal. This has fallen out of favor (maybe favour?) and mass is normally expressed, even in English system countries as kilograms. Weight, force, is mass times an acceleration, normally that of gravity. A kilogram at the surface of the earth will weigh 2.2 lbs, in space (free fall) it weighs nothing, but is still 1 kg of mass.

While I will use feet, inches and pounds until the day I die, the whole concept and practice of English system forces and weights and masses is so screwed up I just surrender to the metric system. Someone will undoubtedly jump in and demonstrate the age of my memories here.

The next subject will be the metric unit "fig".

Wrong here. A major difference between the metric and imperial systems, is that the units are different. Kilogram is a unit of mass, while pound is a unit of weight or force.

Actually the pound is defined as both a unit of mass and a unit of force. A pound mass is accelerated at 32.16ft/sec2 by a pound force. The more "fundamental" unit of mass in the Imperial system is the seldom used unit called the "Slug". A slug of mass is accelerated at 1ft/sec2 by a pound force. On Earth under normal gravity (1.0g) a slug has a weight of 32.16 pounds force.

We both agree here. Read my post #7 where in I describe pound-force as a retronym. Pounds were historically a unit of force, as in psi, and foot pound. However in the metric system, the commonly used unit of measure is kg which is a unit of mass. Lay folks used both terms interchangeable as both mass or force, as in 1kg of cheese is equal to 2.2 pounds of cheese. To reconcile the error, we have the pound-mass, and after a while we coined the retronym pound-force to keep the facts straight.

It's analogous to baseball. We always went to a baseball game in the afternoon. By and by they invented night games, which over time became so popular that we now speak of day games. Day game being a term that was totally unnecessary until night games stopped being the exception.

I got the Park Tools torque wrench, and it works great.

I've been checking some torques from the PDF on this page, and one surprising one is for the quill nut on a threaded headset stem -- around 150 in-lbs or more! I tried that (needed the big torque wrench in the OP), and that was way more force than I would ever have used.