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radius contour
Posted: Tue Nov 27, 2012 3:58 pm
by Haggis
Hi
What technique do you use to draw the line of the radius on the end block and the braces?
thanks
Häggis
Re: radius contour
Posted: Wed Nov 28, 2012 12:37 am
by Ben-Had
I use radius blocks to sand it in thus no lines required. However, I do pencil cross hatches to know when I've reach where I need.
Re: radius contour
Posted: Wed Nov 28, 2012 7:35 am
by tippie53
I do it the same way sometimes I may use chalk
Re: radius contour
Posted: Wed Nov 28, 2012 9:04 am
by justrfb
Good morning All.
I am new and probably wrong but I have to ask... Could someone please clarify the question for me as I thought the radius was sanded on the end block and the kerfing? Thanks for your patients and answer.
Sincerely,
Rich
Re: radius contour
Posted: Wed Nov 28, 2012 11:51 am
by Ben-Had
The guitar is curved on the end block and you need to match that radius rather than have a flat block. So you are putting a radius on the top and back of the block. Same for the top and back braces. Builders use different radii i.e. I use 12' on back and 25' on the top. A flat top guitar usually isn't really flat.
Re: radius contour
Posted: Wed Nov 28, 2012 12:19 pm
by watergunn
I had used sanding sticks on the first few builds. Now I use the readii dishes from Blues Creek.
The process could not be easier and it is repeatable each time.
I chalk all the way around and on the blocks. Then I just turn the dishes until I am even all the way around.
I also use the dishes for gluing the braces to tops and backs as well.
Very easy.
Re: radius contour
Posted: Wed Nov 28, 2012 4:14 pm
by Haggis
Hi
Maybe I should ask like this.
How do I trace the big radius on the end block if its square from the beginning. The radius is quite big ( don´t know how big) and I wonder if you have a method to draw that on the block. If I don´t have the radius disc for the braces, then I need to draw the radius on to the wood to be able to sand it down to that radius line.
häggis
Re: radius contour
Posted: Wed Nov 28, 2012 4:49 pm
by johnnparchem
I have used a template with the right radius to draw the line. I profile the sides to close to the right height. The blocks are glued proud so that I have room for the radii. I then put my template on the sides across the guitar next to the block and trace the line from the template to the block.
If you want to make a template to have basically the right shape and you do not want to make a 16 or twenty five foot compass, you can make it with a flexible rod.
If you want lets say a two foot long template at a 25 foot radius"
On the board you are going to use for a template place 2 pins two feet apart.
We need to calculate the sagitta of an arc from the radius 25' and the cord length 2 feet
sagittal = radius - sqr(25^2 - (1/2 * 2)^2) =
.02' or about a quarter of an inch.
place a third pin 1/2 of the length of the template up 1/4 inch (centered between the two pins up a 1/4 inch). Bend a flexible rod across all three pins - that is your arch! Draw it and cut out your template.
Here is a link for a better description than mine.
http://liutaiomottola.com/formulae/sag.htm
Re: radius contour
Posted: Wed Nov 28, 2012 10:41 pm
by JLT
Haggis wrote:Hi
What technique do you use to draw the line of the radius on the end block and the braces?
thanks
Häggis
I use a wedged sanding stick as described on page seven of the Stew-Mac 000 instruction manual:
http://www.stewmac.com/freeinfo/i-5297/i-5297.pdf
It seems to work OK, once you've figured out what angle the wedge needs to be.
Re: radius contour
Posted: Thu Nov 29, 2012 1:45 pm
by Haggis
johnnparchem wrote:I have used a template with the right radius to draw the line. I profile the sides to close to the right height. The blocks are glued proud so that I have room for the radii. I then put my template on the sides across the guitar next to the block and trace the line from the template to the block.
If you want to make a template to have basically the right shape and you do not want to make a 16 or twenty five foot compass, you can make it with a flexible rod.
If you want lets say a two foot long template at a 25 foot radius"
On the board you are going to use for a template place 2 pins two feet apart.
We need to calculate the sagitta of an arc from the radius 25' and the cord length 2 feet
sagittal = radius - sqr(25^2 - (1/2 * 2)^2) =
.02' or about a quarter of an inch.
place a third pin 1/2 of the length of the template up 1/4 inch (centered between the two pins up a 1/4 inch). Bend a flexible rod across all three pins - that is your arch! Draw it and cut out your template.
Here is a link for a better description than mine.
http://liutaiomottola.com/formulae/sag.htm
Thanks for a very good answer
Häggis