Radius Dishes

[matt301273]

Hi All,

On the plans for the acoustic guitar I am building, it says that the radius for the soundboard should be 28' and 15' for the back...If I were to use radius dishes to get these radii, then the curvature would be like that of the inside of a sphere right?

However, on the same plans, the sides to which back should be glued have a curve which is obviously not a 15' radius curve...They obvious taper in quite sharply on the neck end...And the curve of the sides which takes the soundboard is also not a regular radius curve either....It is higher at the bridge rather than at the centre point

Sooo..Is it a question of getting the radii into the back and soundboard...and then just kind of forcing them to conform the to the different curve of the sides when glueing?

I've seen videos on youtube of guys rotating the sides back and forth on a radius dish with sandpaper to get the back and soundboard to fit more snugly with a less 'stressful' joint...But how can this work when the curve on the sides is not like the curve of a perfect circle?

Any explanation would be appreciated

Matt

[tippie53]

If you use a disk the sides in the mold will conform to the spherical shape. I use this same method. I don't radius the entire top with the 28 radius. The wood will conform to the shape. On the back the plate is also tapered from the tail to the neck and that may be making it look different.
What plans are you using ?
Antes plans are way over built and over braced

[Victory Pete]

If you use a disk the sides in the mold will conform to the spherical shape. I use this same method. I don't radius the entire top with the 28 radius. The wood will conform to the shape. On the back the plate is also tapered from the tail to the neck and that may be making it look different.
What plans are you using ?
Antes plans are way over built and over braced

Hi John
Can you explain?: "I don't radius the entire top with the 28 radius." I bought one of these from you and I havent used it yet to sand the top. How should I procede on a D-28?

Thanks

Pete

[tippie53]

Yes the back is usually 15 foot radius but this is also placed at a taper so the radius is not parallel to the mold but dips about 9/16 to 3/4

the top is not radiused totally at 28 but I use a 3 facet design like martin. The top will then have a 1 1/2 degree angle at the upper part from the sound hole to the neck block the lower end will have a radius and there will be a flat area between the 2. This will by design incorporate stiffness to the top.

Having the fretboard plane straight helps to control that fret board so you have this straight and still have the set up for the bridge correct. Just radiusing the top at 28 foot will make this difficult , If you want to radius the entire top use a 32 radius.

hope this helps

[Victory Pete]

Yes the back is usually 15 foot radius but this is also placed at a taper so the radius is not parallel to the mold but dips about 9/16 to 3/4

the top is not radiused totally at 28 but I use a 3 facet design like martin. The top will then have a 1 1/2 degree angle at the upper part from the sound hole to the neck block the lower end will have a radius and there will be a flat area between the 2. This will by design incorporate stiffness to the top.

Having the fretboard plane straight helps to control that fret board so you have this straight and still have the set up for the bridge correct. Just radiusing the top at 28 foot will make this difficult , If you want to radius the entire top use a 32 radius.

hope this helps

Hi John
I am a bit confused, when I bought the 28' radius board I figured I would be doing the whole top. How do you just radius the lower part? Do I still used this board to glue the braces to the top?

Thanks

VP

[tippie53]

In the video you can see that we only work from the top of the sound hole to the neck block. The creates 3 areas the 2 curved areas and the flat spot. The curvature of the doming helps to create the angle for the neck.
Use the mold for the datum points and measure the dish as you work. Use chalk to to see the removal this helps to see the symmetry