to scallop or not to scallop

Construction and repair of Classical Guitar and related instruments
theknowle
Posts: 115
Joined: Wed Dec 05, 2012 7:50 pm
Location: Staffordshire UK

to scallop or not to scallop

Post by theknowle » Sat May 27, 2017 7:36 pm

Do all of you out there always scallop your fan struts?
It seems that Torres did not always do this and Hauser (1) often only scalloped one end.
Is there any acoustic or structural advantage to scalloping - or is it only a matter of aesthetics for luthiers?
I'd be grateful for any comments/opinions.

Robert England
Luthier
Posts: 1267
Joined: Sat Jul 07, 2007 3:29 am
Location: Toronto, Canada

Re: to scallop or not to scallop

Post by Robert England » Sat May 27, 2017 9:24 pm

I do it, mostly because most of the classical plans I have studied showed scalloped braces. I haven't put much thought into it, but I always assumed that the purpose of the scallop was to gradually transition the stiffness of the brace to the end, rather than creating a sudden "hard spot" at the end of the brace. Maybe one of the members who have done guitar structure modelling will comment.
Robert

theknowle
Posts: 115
Joined: Wed Dec 05, 2012 7:50 pm
Location: Staffordshire UK

Re: to scallop or not to scallop

Post by theknowle » Wed May 31, 2017 10:40 pm

Thanks, Robert.
I wonder - is the general consensus that it makes no noticeable difference to the sound/resonance of the box?

Pat Foster
Luthier
Posts: 16
Joined: Sat May 13, 2017 4:12 pm
Location: Spokane, WA

Re: to scallop or not to scallop

Post by Pat Foster » Wed May 31, 2017 11:09 pm

Scallops do reduce stiffness in the area near the end of the brace, smoothing out the hard spot. Hard spots at the end of braces can lead to peeling the brace away from the top in some circumstances, where the top might flex under pressure and a stiff brace end would flex.
patfosterguitars.com

Douglass Scott
Luthier
Posts: 452
Joined: Fri Nov 09, 2012 5:44 pm
Location: Ladysmith, Canada

Re: to scallop or not to scallop

Post by Douglass Scott » Thu Jun 01, 2017 3:40 pm

theknowle wrote:
Wed May 31, 2017 10:40 pm
I wonder - is the general consensus that it makes no noticeable difference to the sound/resonance of the box?
how fan braces are shaped, including scalloped ends or not, definitely makes a difference. Can't say categorically how much or what difference since it depends on several other intersecting factors as well. Scalloped fan tips can certainly affect resonances, weather it would have enough impact to do what you have in mind is another question.

KamHon Leung
Amateur luthier
Posts: 10
Joined: Fri Mar 31, 2017 1:55 am
Location: Hong Kong

Re: to scallop or not to scallop

Post by KamHon Leung » Sun Jun 04, 2017 1:51 am

Pat Foster wrote:
Wed May 31, 2017 11:09 pm
Scallops do reduce stiffness in the area near the end of the brace, smoothing out the hard spot. Hard spots at the end of braces can lead to peeling the brace away from the top in some circumstances, where the top might flex under pressure and a stiff brace end would flex.
Hi Pat,

Could you please explain what you mean by hard spots at the end of the braces?

Thanks.

Pat Foster
Luthier
Posts: 16
Joined: Sat May 13, 2017 4:12 pm
Location: Spokane, WA

Re: to scallop or not to scallop

Post by Pat Foster » Wed Jun 07, 2017 4:17 pm

If the brace isn't tapered at the end, ending abruptly, it retains its stiffness there. If there's stress on the top at that point, from pressure or an impact, it can cause the end of the brace to separate from the top. The stress can cause the top to sort of peel off the brace, sometimes taking some of the brace with it. If the brace is thinned down close to the top at its end, the end can flex with the top, helping to avoid separating. It can also contribute to a top cracking. It's less of an issue with thin braces which can flex more readily with the top, as most fans are that I've seen in my limited experience in the CG world.

Another issue arises in the active area of the top, say below the bridge, where a gradual change is stiffness is often the goal. An abrupt end of a brace creates an area of concentrated stiffness, which many think is detrimental to sound.

Pat
patfosterguitars.com

theknowle
Posts: 115
Joined: Wed Dec 05, 2012 7:50 pm
Location: Staffordshire UK

Re: to scallop or not to scallop

Post by theknowle » Thu Jun 08, 2017 7:07 pm

Thanks, Pat.
Very interesting. Makes a lot of sense!

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