Difficulties determining Cross Grain mode (fC)

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Edzard
Beefwood
Posts: 23
Joined: Sun Jun 19, 2011 7:33 pm
Location: Eindhoven - Holland

Difficulties determining Cross Grain mode (fC)

Post by Edzard » Sat Oct 11, 2014 12:58 am

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
Excel.jpg (69.54 KiB) Viewed 5214 times
And the following recordings:

Twinsting vibrationmode (fLC) at 59 Hz.
TEST-FLC.jpg
TEST-FLC.jpg (44.01 KiB) Viewed 5214 times
Long grain vibrationmode (fL) at 84 Hz.
TEST-FL.jpg
Then the Cross grain vibrationmode (fC):
TEST-FC.jpg
TEST-FC.jpg (41.05 KiB) Viewed 5214 times
Or moving allong the node line:
TEST-FC02.jpg


and
TEST-FC03.jpg
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

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Trevor Gore
Blackwood
Posts: 1605
Joined: Mon Jun 20, 2011 8:11 pm

Re: Difficulties determining Cross Grain mode (fC)

Post by Trevor Gore » Sat Oct 11, 2014 5:02 pm

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
Beefwood
Posts: 23
Joined: Sun Jun 19, 2011 7:33 pm
Location: Eindhoven - Holland

Re: Difficulties determining Cross Grain mode (fC)

Post by Edzard » Sun Oct 12, 2014 6:29 am

Thanks for the reply and tip!

I will give it a try.


Best regards,


Edzard

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