Not enough bridge rotation

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chrisbaer
Kauri
Posts: 30
Joined: Wed Oct 04, 2017 5:41 am

Not enough bridge rotation

Post by chrisbaer » Fri Dec 14, 2018 3:49 am

So, it's been a few weeks since I've strung up my second Falcate guitar and played around with it. Still sounds great!

I finally got around to testing the degree of bridge rotation and it's only .7 degrees, tested with an iPhone clinometer and some adhesive putty.

String and saddle height are good and it's a light weight bridge and appropriately thinned top. Bridge plate is rosewood. Brace wood is spruce (I'll have to go back and find the YM numbers, but they were definitely in the range specified by the books).

What other factors go into a proper 2 degree rotation?

I'd guess the first culprit would be that the bracing is too tall? I looked through that section in the Design book, but I wasn't clear to me how you would calculate bracing height. Can someone point me to a specific section? I was at 7mm at the tallest places.

Thanks!!

Chris

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Trevor Gore
Blackwood
Posts: 1444
Joined: Mon Jun 20, 2011 8:11 pm

Re: Not enough bridge rotation

Post by Trevor Gore » Wed Dec 19, 2018 8:02 pm

chrisbaer wrote:
Fri Dec 14, 2018 3:49 am
I finally got around to testing the degree of bridge rotation and it's only .7 degrees, tested with an iPhone clinometer and some adhesive putty.
The measurement technique does influence the answer you get. The book techniques notes the use of a neck rest, basically to make sure the guitar remains steady as the string tension is dumped. Using this technique, the measurement includes a component due to the neck/body straightening out as the tension comes off. Depending on how you set up with the iPhone, this whole body unbending may or may not be included.
chrisbaer wrote:
Fri Dec 14, 2018 3:49 am
What other factors go into a proper 2 degree rotation?

I'd guess the first culprit would be that the bracing is too tall? I looked through that section in the Design book, but I wasn't clear to me how you would calculate bracing height. Can someone point me to a specific section? I was at 7mm at the tallest places.
I wouldn't go much lower than 7mm. If your resonant frequencies are too high with braces at 7mm, best to use less stiff brace wood. The cube rule effect will make things very sensitive to brace height otherwise. All the stuff about brace design is in Section 4.4 et seq. If you're pushing for a really responsive guitar, best to use monopole mobility as the criteria and get the resonances in the right places.

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