Back radius question

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gerryt
Beefwood
Posts: 26
Joined: Tue Nov 30, 2010 3:31 am
Location: Moray, Scotland

Back radius question

Post by gerryt » Sat Dec 29, 2018 9:41 am

Hi all

Gerry from Scotland here and newbie to the books.

Quick (and possibly stupid) question - can I get a live back out of a radius that iisn't 3 or around that metres? I've never been that fussed about the size of radius I use for the back and, through no particular reason other than it was sort of traditional, I've been using a 20' radius dish. Well now I'm into the books and I want my first book build to have a live back so....can I achieve that using a 20' radius?

Thanks in advance and apologies if this is a bit basic.

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kiwigeo
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Re: Back radius question

Post by kiwigeo » Sat Dec 29, 2018 10:47 am

The specs in The Books for a live back are based on the radius figures in the books. You can go for a different radius but the way I understand things you'll need to tweak brace stiffness accordingly. I build with a 25' radius back and on my first Gore build I had to play around with the stiffness of the main back cross brace to get the live back working.

gerryt wrote:
Sat Dec 29, 2018 9:41 am
Hi all

Gerry from Scotland here and newbie to the books.

Quick (and possibly stupid) question - can I get a live back out of a radius that iisn't 3 or around that metres? I've never been that fussed about the size of radius I use for the back and, through no particular reason other than it was sort of traditional, I've been using a 20' radius dish. Well now I'm into the books and I want my first book build to have a live back so....can I achieve that using a 20' radius?

Thanks in advance and apologies if this is a bit basic.
Martin

gerryt
Beefwood
Posts: 26
Joined: Tue Nov 30, 2010 3:31 am
Location: Moray, Scotland

Re: Back radius question

Post by gerryt » Sun Dec 30, 2018 1:36 am

Thanks for that Martin. So not impossible to use a larger radius for the back but a bit more challenging. I have some adi spruce which might up the stiffness of the back bracing a bit.

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kiwigeo
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Re: Back radius question

Post by kiwigeo » Sun Dec 30, 2018 8:54 pm

Back stiffness can be most effectively trimmed by adjusting the height of the lower bout cross brace. Stiffness can be reduced by taking wood out from the central section of the brace or increased by carving a flat spot in the central part of the brace and gluing in additional wood.
gerryt wrote:
Sun Dec 30, 2018 1:36 am
Thanks for that Martin. So not impossible to use a larger radius for the back but a bit more challenging. I have some adi spruce which might up the stiffness of the back bracing a bit.
Martin

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