radiusing a soundboard?

I've been doing some reading here in the Luthier's Lounge and have come across a few mentions of creating various radiuses of soundboard (25', 18', etc).
I've tried to do some googling on this subject but have only found fuzzy answers.
How does one radius a soundboard? Is this done in the clamping/go-barring stage? I ran across a few sites that say the soundboard is placed on a concave base plate of a go-bar deck but there weren't any other details other than that.
Do the tone bars have to be shaped to accomodate the radius of the soundboard (or will this occur naturally under the pressure of the go-bars)? And after the glue on the tone bars has dried how does the soundboard keep it's radius?

Yes to all of your questions. Keep in mind that when you are beginning a new craft everything is fuzzy at the start. Even the clearest information doesn't make sense until you've got some experience down. You're not supposed to learn everything at once. One source is not going to give you all the information you seek but rather will be found in small increments here and there.Comprehension doesn't occur until you get you hands on the materials and practice the procedures for a while. It's part of the journey.

A radius dish or board is used for building and bracing the tops and backs. I believe I use 25' for the tops and 15' for the backs. Braces are sanded to the curve of the radius you want. Your glued-up sides (with kerfing attached) are also sanded in a radius dish. This is what helps to keep the domed shape. I use a potter's wheel with radius dishes mounted on it for this purpose but there are other, less expensive ways of doing it. There is lots of information on this topic on the Internet in guitar builder forums and sites if you do a Google search. You'll also find information on how to build dishes, soleras and forms as well.
BTW, radiiusing isn't absolutely necessary but I find it makes for a better instrument. Because of the physics of the domed shape, it allows you to build stronger and thinner as well. Some builders, especially beginners, will choose to keep their sound boards flat and simply bend the backs over the curved sides. As with anything, there are many ways and many degrees of doing things.
Good luck.

Thanks for the advice, Chuck. I'll check out those guitar building forums.

Mahalo!

I did a tutorial article for Uke Talk a while back explaining the process I use for making my domed dishes. I learned from Mike Chock at Hanalima and basically used his information modified to suit my needs.

http://uketalk.com/luthier-tutorials/domed-dish.htm

Yes! That article was a real find for me when I did my dish two years ago. The warning at the end about the dust is not a joke - try doing it outdoors.

I still build with flat tops though, haven't got around to put a radius in my solera (a fact that I guess makes it not a solera).

Sven

Awesome tutorial Dom! I'll have to do a little more research but as I'm an uber-noob when it comes to woodworking, let alone luthery I'll have to plan it for a couple ukes down the line. Maybe one day I'll be building smooth sounding ukes like Luthier Vandross... yeah, I said it! Hello? Is this thing on?

We had an old boy at college who headed up the CDTdepartment. He had formerly worked for Rolls Royce and was an incredible machinist. One prject in the plastics department was making metalaphones. This old boy used to do the metalwork side and always insisted that 'stressing' the bars a little produced a better tone. That is the principle behind doming the front - as Chuck said you can build thinner but also, you have a stronger structure, and in my opinion, a btter tone. I'm just doing a video of a true hand build - it's a concert Vita Uke for which I do not have my standard high tech form. I'll be doing the first part tonight and you can see how I've domed the top...

I'm looking forward to seeing that Pete

I was just talking about this with Rob and Chy in Hebden Bridge the other night. There were three Howlett sopranos in the same pub. You'd have loved it.

A few years ago there was a small piano factory close to me that I was given a tour of. They had an interesting way of putting the crown on a soundboard. There was a tall narrow box with a heater at the bottom that the new soundboard went into for several days until the wood was totally dry. While it was completely dry they glued the ribs on in a flat go bar deck. The crown appeared when the wood reabsorbed moisture from the atmosphere. The side where the ribs were glued was unable to expand but the other side could. He claimed that this produced a better sound due to different tensions in the wood. Anyone fancy doing a uke like that?

I believe that Martin on their guitars originally glued the radiused braces on a flat board and if they sprang back, then hey, curved front...

Dom - I would have made the arc by attaching a router to an 'arm' the length of the radius and cutting a 1/4" template. That's how I did it and then followed your protocol. However I would make one suggestion - glue 2 pieces of 3/4" ply together. I found that over time, my 3/4" board bowed....

Pete Howlett said:

That is the principle behind doming the front - as Chuck said you can build thinner but also, you have a stronger structure, and in my opinion, a btter tone.

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Yes, I neglected to mention that putting the top under tension will yield a better tone. Tension is also the reason a lacquered instrument sounds better in time as the lacquer continues to dry and shrink. Good point.

Do you guys radius the bridge plate as well? I would think you'd have to, but don't really know...I'd like to give this a try on my next tenor as well.

Pete Howlett said:

However I would make one suggestion - glue 2 pieces of 3/4" ply together. I found that over time, my 3/4" board bowed....

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Thanks for the input Pete. I have made one from layers of ply and haven't yet noticed any warping of those made with the MDF.

Flyfish57 said:

Do you guys radius the bridge plate as well? I would think you'd have to, but don't really know...I'd like to give this a try on my next tenor as well.

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If you are talking about the "bridge plate" then you don't do anything to it because it is thin enough to just bend into the shape when you glue it on via the go bar deck.

If you meant the actual bridge the answer is yes. After making the dish and applying the sand paper I take a smaller (6 or 8 inch) diameter piece of mdf and sand it on the dome to create the matching form for the bridge. Put sand paper on it and sand the bottoms of your bridges prior to gluing them on so they match the radius of the top.

Shop built tools - hmmmmmm :drool:

I do the same as Dom only its a 2" x 8" wide piece - easier to hold in your bench vice. You can also stick sandpaper to the skids and use them to shape the bottoms of your braces or make the mono go-bar deck you see in my video.

When I used to make wood bridge patches I would sand the patch to conform to the radiius. I doubt if it's really necessary. But certainly the bridge needs that curve in it.

Moore Bettah Ukuleles said:

When I used to make wood bridge patches...

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What do you do now?

Dominator said:

If you are talking about the "bridge plate" then you don't do anything to it because it is thin enough to just bend into the shape when you glue it on via the go bar deck.

If you meant the actual bridge the answer is yes. After making the dish and applying the sand paper I take a smaller (6 or 8 inch) diameter piece of mdf and sand it on the dome to create the matching form for the bridge. Put sand paper on it and sand the bottoms of your bridges prior to gluing them on so they match the radius of the top.

Click to expand...

Using the "Pythagoras Theorem" I calculate that for a bridge at 2.5" wide fitted to a 22 foot radius, you only have to remove .0029" of material from under the bridge centre to make a perfect fit...Thats about the thickness of a Human hair..

Timbuck said:

Using the "Pythagoras Theorem" I calculate that for a bridge at 2.5" wide fitted to a 22 foot radius, you only have to remove .0029" of material from under the bridge centre to make a perfect fit...Thats about the thickness of a Human hair..

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That may be true (I'm not smart enough for those kinds of calculations ) but using a 20 foot radius my bridge will rock slightly left and right until I sand the bottom and get it fitted properly.

Yes thats true! Dom.. it's amazing how big a few thou: can be, when you are working to fine limits...as I'm finding out on my Dovetail neck joints.