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So, how do they calibrate these anyhow? I think I read somewhere that Sears would calibrate craftsman wrenches. Is this something that someone could easily do with something like a cheapy from Harbor Freight?

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

I know my military avionics friend talks a lot about "cal-ed" tools.
"Cal-ed" tools cost an awful lot more than non "cal-ed" tools or ones that can't even be calibrated.

They have a special device that costs quite a lot of $$$ that is used to determine the calibration of a torque wrench (or multimeter, or whatever you can think of....wire crimpers, etc).

My $12 Harbor Freight torque wrench is used for one thing: lug nuts

When I need one to do precision work, it'll probably have to be a Sears, at a minimum, maybe a Snap-On (ugh, I don't even want to think how much that costs).

step 1. find small child that weights around 50 lbs
step 2. let small child stand on the end of the wrench

bingo....50 lbs...adjust wrench accordingly



ahhh, the first of many smart a$$ comments i'm sure

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05 MCS

You calibrate a torque wrench by using a piece of test equipment that measures torque , duh.....(I wish I could remember what it's called). I had one in my hand a couple of weeks ago.

You set your wrench too say...oh.. 80ft lbs and torque the fitting that is attached to the meter. The meter then tells you how much peak torque you just applied. If your wrench has an adjustment you tweak that until what the meter and the wrench says are the same.

If you have a torque wrench that has no adjustment you can use the above data to create an offset factor. By which I mean, if you know that your wrench applies 80ftlbs of torque when it is set at 78 you always set it 2 low and you should be ok.

For really, really sensitive stuff, Buy a really good torque wrench. For most of the stuff we do it probably doesn't matter to much as long as it's close. (YMMV)

On an interesting related subject I read something today about angular torquing of stretch bolts in modern engines. I guess instead of tightening bolts in a series of steps up to the specified torque, in newer engines you tighten to a lower value and then add say 90 degrees of twist from there regardless of torque value. I guess the reason is because the stretch bolts require so much torque to overcome the thread friction that you can't reliably torque them to the correct amount of stretch.

Are you bored yet??

ummm, no.


I had always wondered if I was to have some calibrated true weights and a bar (like a lever, but to generate torque) with connection points at .5 ft, 1ft, etc. on one end and on the pivoting end a connection for the torque wrench. I could setup test to try to lift the bar off of a horizontal resting point using specific torque settings. This could be used to determine both repeatability as well as an adjustment chart.

known dist
=========O-------+++++ <- wrench
|
|
W <- calibrated weight

Also, I have heard that the deflection beam types are more accurate than the 'click' types. So if I had a beam type that was known to be accurate, I could mate the two wrenchs together (one again using some type of jig) and then calibrate one wrench (cheap click style) against the known beam style?

_________________
Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.com
Money can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.

Another thing to consider is that most torque specs are "dry" value. If its a fitting that you typically apply some grease to (i.e. spark plug threads) then you need to change the dry torque value by a percent thats tied to the type of grease. Typical value changes are in the 20-30% range IIRC.

And remember to keep your hand perpendicular to the the bar of the torque wrench and placed on the grip section as the "Lever arm" length *is* important .

Torque = Force X Lever arm

where that "X" (cross product) equals "1" when the force is applied perpendicular to the Lever arm. Otherwise multiply by the sine of the angle ... aw nevermind.

Probably more than you care to know, I'll go back under my rock now ....

Frank

Where you hold the torque wrench is not too important since the handle grip is located on a pivot pin. The pin determines the "length" of the lever arm (unless you tip the handle so that one end of the handle is contacting the wrench handle, in which case the moment arm is moved to the contact point).
I have used my torsion beam troque wrench to calibrate my "clicker". Just put the same size socket on both wrenches. Put a nut and bolt together so that the bolt is in one socket and the nut in the other. As I remember....I held the "clicker" handle grip in my vise (gently) and made sure that the handle grip did not touch the handle while I applied torque using the torsion beam wrench. Watch the beam indication and listen for the click. You will probably not repeat better than 2 pounds, but, hey close enough for lug nuts.

I even calibrated my air pressure gage using a digital pressure gage accurate to 0.01 psig. That was an eye opener. My gage read over by 2 psi, and Peter's gage read 4 psi under. When we started using his new gage to check his tires, he got slower....now we know why.
Charlie G

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1998 BMW Z3
1987 BMW 325is
2000 BMW
1996 F250 Turbo Diesel

Not sure I follow the "pivot pin" part. My clicker is a solid shaft at the handle end (at least I think so).
Absolute measurements are always tough. 20+ years ago I used to get to work with the National Bureau of Standards. Quite a bunch.
Frank

My bad. The pivot pin on a "clicker" type wrench is internal. The hand position on the external handle makes no difference at all to the reading on this type.
On the other hand, the torsion bar type actually uses the length of the handle for the flex beam. In this type the length is determined by the distance between the socket and the pivot pin in the handle. Sorry for the confusion.
Charlie G

_________________
1998 BMW Z3
1987 BMW 325is
2000 BMW
1996 F250 Turbo Diesel

i guess this means my 1993 VW has a modern engine sweeeeet. seriously though. the manual says to torque to X ft-lbs, then turn another 180 degrees, then another 90. there are a couple likely reasons.

1 - it's torqued in stages to keep the heads from warping. the torques are very high and with soft alloy or just plain aluminum heads, it's easy to warp it if you fully torque one bolt at a time. this way, you effectively torque things down in a gentler fashion.

2 - sometimes, the torque applied isn't an accurate measure of 'how tight' the bolts should be, particularly for stretch bolts. some bolt makers like ARP will say how much the bolt should stretch when it's at the correct 'tightness'. since we can't really measure that with all that metal in the way, they approximate what it takes to stretch the bolt X amount in terms of torque and/or rotations. now they're bored...

oh yeah, it doesn't really matter if you pull on a torque wrench perpendicular to the radius or not. the rotational action of the drive will only 'use' the tangential component of your force in turning the bolt. all the other force you apply is a radial component directed towards or away from the center of rotation, hence it's wasted. so, for a well made wrench, it don't matter none, but you'll just be wasting your breath

edit...more ideas

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1993 VW Corrado VR6 - DSP15 (RIP)
1986 MB 190E 2.3L 16v - STX (SOLD)
1997 BMW M3 3.2L - BS for now