radius contour

[Haggis]

Hi
What technique do you use to draw the line of the radius on the end block and the braces?
thanks
Häggis

[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.

[tippie53]

I do it the same way sometimes I may use chalk

[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

[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.

[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.

[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

[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

[JLT]

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.

[Haggis]

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