Difficulties determining Cross Grain mode (fC)

[Edzard]

Hello All,

I several tops where I have troubles finding the Cross Grain mode. When I tap/recored I find (mostly) two frequencies which stand out.

For example I have this top:

Excel.jpg (69.54 KiB) Viewed 5854 times

And the following recordings:

Twinsting vibrationmode (fLC) at 59 Hz.

TEST-FLC.jpg (44.01 KiB) Viewed 5854 times

Long grain vibrationmode (fL) at 84 Hz.

Then the Cross grain vibrationmode (fC):

TEST-FC.jpg (41.05 KiB) Viewed 5854 times

Or moving allong the node line:

and

With F Cross at 185 Hz I get a Elong/Ecross of 0,78.
With F Cross at 87 Hz I get a Elong/Ecross of 63.4 (which seems very high).

Can I therfore exclude the 87 Hz mode for the Cross grain?

Thanks again for your input.

Best regards,



Edzard

[Trevor Gore]

Checking P 4-63, Table 4.5-3, I'd say the 185Hz figure is likely the correct one, given the thickness you have.

You might try using G-tune, which I find easier for this sort of thing. Downloadable from here:

http://www.jhc-software.com/downloads.shtml

Double click on the frequency meter to get a larger display...

[Edzard]

Thanks for the reply and tip!

I will give it a try.


Best regards,


Edzard