Need info on radious of tops

[Donald A. Fortune]

I'm looking for info on top radious for a drednaught guitar - also the back radious-

common numbers are ok -- thanks in advance for any info thet is out there..

Peace, Donald

[FRANK]

I have seen 50 foot and 30 foot tops and 15 foot back for radius

[Donald A. Fortune]

thanks Frank- Im using a 1/4 inch rise in the middle of a 18 inch run and was wondering what my radious was

the neck tilted bask at a 1-1/2 degrees seems to be ok but I was wondering what my radious was...

hope you understand what I am saying here---  peace 

[Jeff Highland]

25 or 28 foot is a common radius for the top though some build flat too..

15 foot for the back is pretty normal practice.

 

Often the UTB above the soundhole is kept flatter to improve the match of the top to the underside of the fretboard

[Tim Mace]

How do you arrive at a 20'-50' radius on a brace for instance? Do you have a template to match it to?I think that's what Donald might be asking.Also I read(Cumpiano notes) that if you plane the neckblock to match the neck angle you get a better fit and also leave the upper brace flat as Jeff suggested.

I have to admit I don't know how to calculate a 50'curve(radius)to be able to say that's what it is!

Lately I've used a piece of maple curved to a radius I think looks good and copy it onto my bracewood

but have no idea what the acual radius is.For example": L13", 7/16" rise at center.What radius is this equivalent to?Very Inerested..........!!!Is there a chart somewhere?

[Jeff Highland]

Heres a calculator

http://liutaiomottola.com/formulae/sag.htm

You have to insert length and radius to give sagitaw (offset in the middle)

Doesnt work the other way around but try a radius or two until you get close to your measurement

[Donald A. Fortune]

Hi Jeff- The reason Im asking the question on radious is because I want to buy a radious form from LMII ans was wondering what was common for a guitar top-- I think I can get away with almost anything for the back but the top needs to be pritty well percise because of the neck,ect.

I have been using a series of clamps to glue up my bracing but it is geting "old" if you know what I mean..I want to use a go bar system..

The templates are too pricy to buy more than one so thats the reason for the origonal question.

[Jeff Highland]

Personally I build my tops  flat and dry and end up with just a little rise in the soundboard.

I use an elevated fretboard so alignmetn with the top is not a big deal

Anything less that 15 looks too flat on a back for me.

Go Bars are great, you wont look back.

You might get a better price elsewhere on the radius disc

Luthier suppliers has a combination top/ back disc

http://www.luthiersuppliers.com/products.html

[William F.Eden]

 I built my owen go bar jig Donald and made the dishes out of Baswood it is very easy.You just draw the outline of the guitar you want to build and take a 5" disk sander and scoop  it out. MY mesurments are in the centre of the back across from side to side 3\6ths and from bottom to top 1\4" to  So you will start from 0 and   end   with 0 on that taper from the patern. And the top you do the same the top mesurments are 1\8th from side to side and 3\16ths from end to end .I hope this is of some use to you .Good luck  Bill.'''''''''''''''''''''''''''

[Jeff Highland]

If you want to use it for radius sanding the rims/linings, a 2' dia circular disc is a better idea, than one just scooped to the outline.

[Doug T]

I use 50' on my tops, glue in the neck brace and bridge patch flat, then glue up the rest of the braces and tone bars at 50'.  What happens is that the neck area is pretty flat and the rest of the body is arched, less end to end than side to side.  Does that make sense?  The back is 15'.  I have a jig that allows me to route accurate curvature to the arched braces/bars and then I slightly over-arch the ends.  I feel it adds some spring to the ends.