sidsel.svein(at)oslo.onli
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 Posted: Sun Sep 10, 2006 8:46 am Post subject: Prop. bolts |
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WARNING: Only for the keenly interested!
Philip,
I take it that the chart you refer to is unique for each torque wrench (or rather, wrench handle length), and that it gives adjusted torque setting as a function of spanner length.
You are correct in that the angle of pull makes no difference, PROVIDED the wrench handle is on a straight line extension of the spanner. Pulling at
any angle other than at right angle to the handle will then set up only an axial force in the wrench/spanner combo and a shear force on the bolt head,
not an added torque. If the wrench handle is at an angle to the spanner, however, it will matter which angle you pull at and the correction factor in
the table cannot be used. Any handle angle away from straight line makes the effective distance from your pull to the bolt shorter (reduced moment arm),
i.e. reduces the torque on the bolt even if the wrench torque setting remains unchanged.
Wrench and spanner at right angles: As you will see from my attached illustration, the spanner length becomes immaterial, as it does not contribute
to the torque acting on the bolt if you pull parallel to it (it does not contribute to the pull's moment arm). The advantage of the method I described
is that you do not need a correction table, you can set the prescribed bolt torque directly on whichever suitable wrench you have at hand.
If you decide to change to a different length spanner you do not have to remember to re-set the torque limit. The only thing to remember is that your pull must be
parallel to the spanner. It makes no difference if the wrench is not at right angle to the spanner, but it is more natural to pull at right angle to the wrench handle
and therefore right angle orientation of the two tools is recommended. An illustration of the result of not pulling parallel to the spanner is attached, to emphasize the importance of this point.
Best regards,
Svein
PS: In case anyone should question why it does not in itself matter if the wrench is not at right angle to the spanner as long as your pull is parallel
to the spanner: The moment arm does become smaller, but as you are still pulling parallel to the spanner (Rule 1 and the only rule!), now at an angle
other than 90 degr to the handle, your pull must be correspondingly stronger to reach the torque limit set on the wrench. Once the limit is reached, the
moment "travelling" down to the prop.bolt is the same as set on the wrench.
Example: If the wrench is at 45 degr to the spanner but your pull is still parallel to it, the effective moment arm (effective wrench handle length) is
1/1.41 of the handle's actual length, and you must pull 1.41 times harder to reach the torque limit set on the wrench. Can of course be proven
mathematically, but trust this suffices!
----- Original Message -----
From: "philip george" <philipgeorge347(at)hotmail.com (philipgeorge347(at)hotmail.com)>
To: <europa-list(at)matronics.com (europa-list(at)matronics.com)>
Sent: Saturday, September 09, 2006 12:44 PM
Subject: Re: prop bolts
| Quote: |
Rowland I was at one time a Snap on tools dealer and Snap on used to
produce a chart for use with torque adaptors for use in this situation ie.
any adaptor offsetting the torque length as used on for example . V12 Jag
cylinder heads when the casting overhangs the head bolts . the angle that
the torque wrench is pulled makes no difference (unless someone corrects
me)
|
| Quote: | >>principle.
>
>Svein - your diagram is excellent and clearly shows what you mean to do -
>but I'm having trouble understanding how this ensures correct torque at
the
|
| Quote: | >prop bolt.
>
>Initially, I thought it was fine, but when I try to analyse what is
>happening in terms of the forces that are being applied at various
points,
|
| Quote: | >I don't seem to be able to extract a sensible answer.
>
>I also imagined a different geometry - such as the torque wrench in line
>with the ring spanner - and it seems that wouldn't work unless the torque
>setting was adjusted to allow for the relative lengths of the torque
wrench
|
| Quote: | >and spanner.
>
>Can you (or anyone else) offer an explanation of why the 90-degree
geometry
|
| Quote: | >works?
>
>regards
>
>Rowland
>--
>| Rowland Carson PFA #16532 http://home.clara.net/rowil/aviation/
>| 750 hours building Europa #435 G-ROWI e-mail <rowil(at)clara.net (rowil(at)clara.net)>
>
>
>
>
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torqueing_force_at_angle.pdf |
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