View Full Version : Most commonly used radius dish specifications?

08-02-2017, 12:25 PM
I am building a tenor ukulele for my first instrument and I happened across a go-bar system with a 20 ft radius dish and a 28 ft radius dish. I have used the 20 ft for the top. Borrowed a friend's shop and 12 ft radius dish for the back. I plan on building acoustic guitars and perhaps a few ukuleles. I wonder if anybody can specify the several most common radiuses people are putting on their instruments. At $100 a pop, I don't think I want to purchase eight or ten of these.

Thank you for your help!

Beau Hannam Ukuleles
08-02-2017, 01:51 PM
For uke and guitar
Back- 15'
Top- 25' to 30'

Pegasus Guitars
08-02-2017, 02:01 PM
I would have used the 28' for the top. The tighter the top radius is, the more difficulty in fitting the neck joint, neck extension, and the bridge. I use 30' for most of the top and 15' for the back on guitars and ukes. The 12' you used is a common back radius too. Truth is that I doubt many of us actually end up with the radius we try to. Certainly for most shop made radius dishes, the true radius actually varies a bit from the one we tried to get. Even CNC made dishes often don't stay in the radius they were machined to. Whether the back is 25, 28, or whatever does not matter that much. If the top varies a foot or 2 from what you try to get does not matter either. Most builders use a flatter radius though, 25' or more, all the way to flat.

08-02-2017, 02:25 PM
And with the above info, you will also get some spring back, as well as even slight variations in humidity will change the doming that you had planned on. It's something that we all have to plan for and need to be able to fit parts on the go.

08-02-2017, 07:21 PM
I don't radius my tops at all. Flat top ukes. I know, I know. But it eliminates all sorts of complications and they sound great to my ear and there is plenty of history with flat top guitars. Structurally is it as strong as radiused? Maybe not. But a helleva a lot easier to pull off... My backs however are radiused to 24" (2 feet!) which is pretty radical compared to stuff like 24' feet which has got to be pretty subtle. I'm definitely still working all this out and what different radiuses sound like in relation to body taper. So I use a 1/4 inch taper (over a 12 inch body) with a 2 foot radiused back. I like to think it focuses the sound, but what do I know? My new thinking is decreasing the back radius a bit, increasing the taper by an 1/8 and increasing the side depth by a quarter. The theory is... hell I don't know. I just think that might sound good. We shall see. The proof is in the pudding. This is where the real fun comes in I think. Groping in the dark? Definitely.

Michael N.
08-02-2017, 08:57 PM
I wouldn't worry about it, not on an instrument with such a small soundboard aggregate. I'm not sure I'd worry about it on a soundboard with a large aggregate.
I've built numerous flat top guitars. I've never ever thought they were compromised in terms of tone.
Hauser I built flat. That was the N. European tradition of building guitars. When he was asked to build in the manner of Torres he obviously noticed that the Torres soundboard was domed. I'm far from being an expert on Hauser but my understanding is that Hauser I did not dome the soundboard but put a radius to the underside of the bridge. He then 'pressed' the soundboard up into the curved bridge in the process of gluing it. I've tried this method on one guitar and it did introduce some sort of dome into the soundboard. My guess is that Hauser I wasn't aware of the dished out solera and the method of press forming struts.

Pete Howlett
08-02-2017, 09:34 PM
I radius the front south of the soundhole... north is flat. Domed fronts avoid 'Hawaiian belly'.

Beau Hannam Ukuleles
08-03-2017, 06:25 AM
I radius the front south of the soundhole... north is flat. Domed fronts avoid 'Hawaiian belly'.

I do the same-

Pete- Out of interest- do you radius the whole top (i mean sides) then flatten the upper bout or flatten the whole thing then radius just hte lower bout? Ive done both but usual the former.

Pete Howlett
08-04-2017, 01:21 AM
Na... I just leave the top flat. You get a bow like curve in the front which sands out when the linings go one and naturally 'feathers' the edge of the instrument. I get a great sound from my instruments by not 'over-thinking'. If I got involved in radiusing the front I'd need to alter my assembly technique too radically and this would include introduce unwanted variables which I would have a struggle mentally to resolve and justify.