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@hotmail.com>
Sent: Saturday, September 09, 2006 12:44 PM
Subject: Re: Europa-List: prop bolts
<philipgeorge347@hotmail.com>
>
> 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)
> any Snap on dealer should be able to supply the chart . Philip George
>
>
> >From: Rowland Carson <rowil@clara.net>
> >Reply-To: europa-list@matronics.com
> >To: europa-list@matronics.com
> >Subject: Re: Europa-List: prop bolts
> >Date: Fri, 8 Sep 2006 11:00:01 +0100
> >
> >
> >
> >>I have attached (I hope it comes through!) a rough sketch
illustrating
the
> >>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
> >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,
> >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
> >and spanner.
> >
> >Can you (or anyone else) offer an explanation of why the 90-degree
geometry
> >works?
> >
> >regards
> >
> >Rowland
> >--
> >| Rowland Carson PFA #16532 http://home.clara.net/rowil/aviation/
> >| 750 hours building Europa #435 G-ROWI e-mail <rowil@clara.net>
> >
> >
> >
> >
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