How to make a Radius Dish

Does anyone build a uke with the top arched across as in your drawing?
 
22' radius south of the soundhole - keeps the front in lsight tension and the top flat.
 
I love maths....it makes building things so much easier!! I will most certainly be trying this method very soon!
 
How to find R

How to find R? I'm looking to make 2 for my guitars 28' and 20'
 
....You really should write the book Pete.;)

The DaHowlett Code

But your correct Dave- The market is ripe for a extensive uke construction book on par with the Somogyi and Gilet/Gore books.
 
How to find R? I'm looking to make 2 for my guitars 28' and 20

Unless I misunderstand, you seem to have answered your own question. r is the radius of the dish you're making. So r = 28' or 336" for one dish; r = 20' or 240" for the other. So the sagitta for a 24" diameter dish with a 336" radius is 0.214", and the sagitta for a 24" diameter dish with a 240" radius is 0.30".
 
So if you're making a domed front or back, rather than an arched one, a spherical dish is better as the shape is the same wherever you are on the dish.

One of the problems with making arched tops or backs is that, for the braces to fit the arch properly, they have to be sanded by holding them in the position they will be in once installed, and rubbing longitudinally in the trough (if you see what I mean).
Braces.jpg

However,
Assuming one is using a "normal" fan Uke bracing, there is no radiused brace that intrudes into flat territory. Therefore you can get both flat and arched areas by using a commercial domed dish. For the top, 1-grind the sides in the dish to fit the dish , 2-install linings. 3-Grind these linings to fit dome. 4-Grind the upper bout area only on a flat surface till flat- (a few quick swipes). Now you have what Pete has- Flat from head to sound hole, arched/domed south of the sound hole. Requires two gluing procedures though.

If no radius dish. Take a sharp block plane (oh the horror) and take about 1.5 mm off the lower bout sides and about 1mm off the end block area with a smooth transition into your 1.5mm lowered sides. Now you have an arch old skool. I did that for years on guitars (From memory-3mm sides, 2mm endblock for a 33 foot radiused guitar top)
 
Last edited:
Here is another version of "router on a sled" method. Looks even simpler to meIMG_1484.JPGIMG_1487.jpg
 
Router on a sled? Was that the sequel to Snakes on a plane?

But to be serious, that looks like an ok setup. There's more than one way to skin the proverbial cat.

(Tries to erase pictures of doing so with a router, from head)
 
tl;dr

410179261_1f2c5d56dc.jpg
 
This thread got picked up on another woodworking forum, and I glanced through it.

The single curvature mold is probably better than the conical one, there really isn't any reason to build a conical arch into the soundboard, because the wood is already stiff in that direction, and therefore deforming it, is making a lot of weird things happen. You are building a pre-stressed structure in the direction of the stings, and then throwing an s curve into it such that the deformation in the direction of the soundhole (what we seek to avoid), is actually releasing the pre-stress.

(Pre-stress is above my pay grade, but it is the weird world where bicycle wheels support their weight on columns of the spokes between the ground and the axle, contrary to the perception that they hang from the spokes.)

The transverse curve is traditional and does not do bad things to the wood given that it flexes easily in that direction, and it stiffens the board in the same direction as string pull. Some nylon string guitar theory is based on the idea that a relaxed soundboard is a good soundboard.

Uber jig master, and teacher to the many, Charles Fox, has recommended this style, or uses it.

The only downside is that it makes the guitar look a little funny; you can see the curve a little since the fact it runs transverse only, leaves the rim of the guitar at different heights. It is subtle but if it isn't something folks are clamouring for, so it isn't going to help sales.

There are a variety of reasons why spherical molds are used:

1) Once you tool up it is actually easier to build this way, and everyone seems to be tooling up;

2) It has a strong chance, as also with the OP/Fox method of reducing board splitting due to misuse, or too much travel.

3) The bridge dive thing; one way of addressing that.

4) I has virtually become mandatory in custom type instrument builds.

Someone mentioned it is traditional which it is not, depending on your time horizon.

Ukes on the other hand:

1) Use some tough woods that are heavier and thicker than guitar woods

2) Light string tension

3) Hawaii doesn't seem to be splitting, how is it working out in world trade?

4) Top are tiny, which also reduces splitting.



I turn my workboards on a lathe, which takes a pretty big lathe for a guitar, but for a uke, not really. I use spherical boards, because everyone else does, though I use as little as possible.
 
Good day, all. I'm planning to build a 'no router' dish, but am trying to understand comments about arching the soundboard below the sound hole but keeping the top flat above the sound hole under the fretboard. How is that done?

I'm thinking that you use a dish, and you keep the lower bout centered where the curve is as designed (i.e. 22' radius), but the upper bout will see the design radius longitudinally, but will see a flatter radius laterally. Or am I just over thinking this? Grin.

Thanks for any insight.
 
So I can't view the pictures that are posted all it says is to enable 3rd party hosting - do I need to do that or does the OP? (Dave) or are they hosted somewhere else?
 
It's Photobucket's fault. It was a free service for many years but recently they started charging for hosting photos. So old links won't work.
 
Last edited:
Top Bottom