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Torque wrench types (was: Re: Tightening head bolts onenginestand?)

Toby,
  Yes, the clickers should be calibrated, but unless you use this type on a daily basis (and how many of us do?), an annual calibration is sufficient....and good peace-of-mind that's worth the cost.
  I agree with you on the beam-type not going out of calibration; unless you bend the 'pointer' or REALLY abuse the beam (I can't imagine most people being capable of bending that thing unless they do it deliberately), it should never need calibration.
 And, by the way, if you like to "see" the torque coming up on the beam's scale so you can back off before you get to the prescribed torque value....why use a torque wrench at all?
 As you said, the clicker is more consistent as it takes more of the human element out of it.
Whereas the beam-type takes more of the mechanical element out of the equation and puts the burden on the human.

 I'll take consistency over "accuracy".  Consistency is usually more important.
  For instance:  you are torqueing ten head bolts down.  Recommended torque is 100ft/lbs.
With the clicker, you set it for 100ft/lbs, put you are only getting 98 in actuality (accuracy is usually +/-2% on these things)...BUT you are getting 98ft/lbs on all ten head bolts.  Results: happy engine.
Now, do the same thing with the beam type.  You get 99, 98, 100, 101, 100, 100, 102, 98, 99, and (distracted by the neighbor girl walking by in her new bikini) 87ft/lbs.  ....you AND your engine will be unhappy.
See my point?  ...and I defy you to eyeball within 2-3ft/lbs on the scale of most beam types. If you have one, you'll agree with me.
Parallax enters into the picture as well.
 I believe the overall advantage goes to the clicker.  
I'm not trying to bring you over to the "other side", I don't expect you to change your mind, just want to point out some valid arguements.

Larry  




  I chose "after a long time and/or a lot of use" because I think this
  describes a typical scenario. If you have money to burn getting your
  torque wrench calibrated on a monthly basis, go for it. I'd rather save
  the hassle and have a little less precision.

  Have a look at:
  http://www.wildwestcycle.com/f_torque.html

  (Scroll down to the "Torque Wrenches" heading.)

  > Those pointer types get weaker and weaker with use, so therefore the more you
  > use it, the likely you are to be under-torquing...

  I disagree. The principle is simple.. I'm not an ME but I'll throw
  out my explanation. Metals have an elastic region, and a plastic region.
  Elastic means that it can be bent, but only so long as the force holds it
  as such.. after the force is removed, it returns to its original shape.
  Plastic means that it changes shape as a result of the force. I think
  that's pretty clear. Anyway, the elastic region happens before the plastic
  region. Kinda like how things get hot (which is undoable) before they burn
  (permanent).

  The (simplified) idea behind the pointer type is that you have a bar that
  bends within the elastic region, and a bar that doesn't bend at all. The
  relative difference between them is proportional (and hence, a scale can
  be drawn) to the torque applied.

  Now, if you exceed the elastic region and go in to the plastic region, the
  torque wrench will look like a bent golf club. But the deformation will be
  obvious..

  > At least, this is what I have been told (by folks much smarter than I)...

  I told you that?? :))

  But seriously..

  The clicker type works on friction and springs.. and is thus subject to
  wearing of the friction surfaces and aging of the springs.

  I've stripped and broken many bolts by trusting the clicker type. Since
  then I've switched to using the pointer type almost exclusively because I
  can see when I'm getting close and if I decide to compromise (not tighten
  as hard as I had planned), I can see by how much.

  To me, the clicker type is like having a "Engine overheated" led on your
  dashboard versus having a coolant temperature gauge.

  My 2 cents..

  -Toby

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