Torque wrench trivia

[Hirsch <Catenary@xxxxxxxxxxxxxx>]

Paul Rollins wrote:

> Are you using a click style torque wrench? If so, check the
> calibration. They do get out of spec in time. At a recent
> tech session, the speaker said that the racecar mechanics
> with whom he had worked had their expensive t-wrenches checked
> about every six months (and the wrenches were usually out of
> spec).

For the torque wrench buffs among us, there is an article on
torque wrenches by local St Louis AROC club member Charlie
Zarek at the website:

   http://www.catenary.com/victor/isaluti

Select "Feature stories," "General Technical," and "Up Tight with
Torque Wrenches." A few excerpts:

* The torque wrench as it is know today was a development in the
  mid 1930=92s of the Chrysler Corporation and a company known as
  Micromatic Hone.

* The direct-reading bending beam type is the most rugged. While
  other types are affected by wear and fatigue, this tool will
  remain accurate so long as the beam is not actually broken
  and the pointer is set to zero.
  =

* The disadvantages of the bending beam configuration are: =

  1) The measuring scale must be visible.
  2) It is difficult to pull to exact values.
  3) Handle lengtheners cannot be used. Force must always
     be applied to the beam via the handle pivot.

* The toggle action torque wrench (click-type) has now taken
  the predominate place in the auto shop due mainly to the
  availability of inexpensive tools of this type and overall,
  ease of use.

* The advantages of the toggle action torque wrench are: =

  1) One can easily get repeatable applications of torque.
  2) There is no need to see the measuring scale of the
     wrench when in use.
  3) The drive end is fitted with a ratchet.
  4) It is relatively cheap to buy.

* While the toggle action wrench is subject to wear, the
  repeatability remains pretty consistent during a use
  session although the dialed in accuracy may degrade
  with improper care.

On this last point, I was looking at the operating instructions
(8-'79) that came with my old click-type Sears MicroTork torque
wrench and noticed the following warnings:

* When the wrench is not in use, keep it set below 25% of
  capacity. If, accidentally, you leave the wrench set at a
  reading over 50% of of the wrench capacity for more than a
  few hours, set the wrench at the lowest setting and leave
  it there for a minimum of 4 hours before using it again.

* Periodically, the wrench should be checked for accuracy.
  This should be done regularly if the wrench is used frequently
  or is subjected to abnormal handling or storage. In assembly
  line type of usage, the wrench should be checked every 10,000
  cycles (torque applications).

For more info, see the article.

Rich

Editor, i Saluti, St Louis AROC
Website: http://www.catenary.com/victor/isaluti

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End of alfa-digest V7 #298
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