# Re: 6 "piece" PU's

"Clifford Heath" <no@xxxxxxxxxxxxxxx> wrote in message
news:4375b55c\$0\$26981\$afc38c87@xxxxxxxxxxxxxxxxxxxxxxx
> Jon Slaughter wrote:
>> ok, I suppose I wasn't looking at it right. I saw the "beam" being
>> compressed/expanded but I wasn't thinking that when it would "bend" that
>> compression/expansion was involved.
>
> Just to add to this. The way the beam stiffness is calculated from
> Young's modulus is to integrate from some starting point across the
> cross-section area of the beam, the expansion/contraction in length
> required to bend to a specified curvature. There will be a point
> called the centre of flexion where the compressive stress one side
> matches the expansive stress on the other side, assuming the overall
> beam isn't under longitudinal stress as in a guitar neck. If there
> is a net longitudinal stress, that will be the difference between
> the compressive and expansive stresses from bending, and it moves
> the centre of flexion.
>

hmmm... I think I got that.

> So in a guitar neck, the neck is in overall compression. The flexion
> is towards the string side, so there is more compression on the
> fingerboard side than there is expansion on the back side. So the
> centre of flexion is closer to the fingerboard side, which is why
> a straight single-acting truss rod works when it's placed down
> the back of the neck - it's behind the centre of flexion and hence
> counteracts the string forces. If it ran right down the centre of
> flexion it would shorten the neck without adding a bending moment.

ok. not only would it shorted it it would probably create some type of warp
in the neck? (you have two forces acting in opposite directions(The truss
and the flexion(well, the force that cases that point) which causes a

I assume the centre of flexion isn't directly in the center of the
neck(lengthwise) since necks have tend to decrease in width as you move down
to the nut(atleast in the bolt on necks I've seen)? So if I were to make a
neck how do I find this center of flexion experimentially?

> Clifford Heath.

Thanks again!

Jon

.

## Relevant Pages

• Re: 6 "piece" PUs
... There will be a point called the centre of flexion where the compressive stress one side matches the expansive stress on the other side, assuming the overall beam isn't under longitudinal stress as in a guitar neck. ... the neck is in overall compression. ...
(rec.music.makers.builders)
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(alt.guitar.bass)
• Re: 6 "piece" PUs
... > Jon Slaughter wrote: ... >> I assume the centre of flexion isn't directly in the center of the ... > line down the middle of the neck wood where there's neither compression ... by integrating the ...
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