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Message started by konacat on Jul 6th, 2005 at 8:36am

Title: Radius on soundboard and back
Post by konacat on Jul 6th, 2005 at 8:36am
Building a ukulele is on the back burner but it still in my long-term goals. But I do think about building and read these posts to increase my understanding. Thanks to everyone for providing good information.

I realize many people use a radius on tops and backs but I'm not sure on a couple of things.

1. Do the backs and tops get their radius from being glued to the bracing?

2. If the top and back have a radius and are then sanded flat at the edge for gluing to the sides does it make the edge weaker?

3. Does using a radius make binding more difficult?

4. I have a Les Rietfors concert uke that a very deep back. It appears to have been bent as it is not a radius. Has anyone tried bending a back into deeper shape?

As soon as I can get some room in the garage I'd like to give building a try. Only other problem is I keep getting better at poker. Building is still a goal.

Title: Re: Radius on soundboard and back
Post by Kevin on Jul 11th, 2005 at 12:37am
Hey konacat... Although there are better-experienced people that could answer your questions, I notice that no one else has come forth. Here's your Q&A according to my one year of hobby-building experience:

1. Do the backs and tops get their radius from being glued to the bracing?

Yes, the braces are radiused, or arced ranging from as relatively flat as 30 degrees to as much as 12 degrees. Rounder radius, such as 12, is often used on the back while the top may be a minimal radius like 20-25, but just enough to create a slight doming effect, strengthening the surface to counteract the pulling up and down tension of the strings. When gluing the top and bottom plates to the braces, the wood will follow the arc you have established.

2. If the top and back have a radius and are then sanded flat at the edge for gluing to the sides does it make the edge weaker?

You'll generally angle-sand the kerfing to match the bracing, therefore the top and back plates will seat "right on" to your sides. Lots of info available on how to this, let me know if you need more. Some methods employ using more than one radius length on the top, with the greater radius being nearest the bridge and the others being somewhat flatter but still some arc.

3. Does using a radius make binding more difficult?

I've never installed binding, but there are various binding tools that should work well under any circumstance, such as the Dremel attachment sold by StewMac. However, since almost all stringed instruments have a slight radius, I suspect that conventional routers with the right bits pose no problem.

4. I have a Les Rietfors concert uke that a very deep back. It appears to have been bent as it is not a radius. Has anyone tried bending a back into deeper shape?

Sounds like you're referring to a back that is more dramatically sloped front to back due to a greater thickness at the the end and a lesser thickness at the heel of the neck? If so, you're merely cutting the sides at your desired angle, and the back plate will easily follow that slope when you glue it on.

Hope this helps!


Title: Re: Radius on soundboard and back
Post by konacat on Jul 11th, 2005 at 10:39am
Kevin, Thanks for the reply

Title: Re: Radius on soundboard and back
Post by Road_Toad on Jul 11th, 2005 at 7:08pm
Hi konacat,

I'll answer on number 3- I do a radius on all my backs and I do binding on all instruments. I use a hitachi laminate trimmer with a tilting base. I just tilt the base to roughly match the pitch of the radius. The trimmer also has a roller bearing to adjust the depth. I've had no problem routing the binding channels. Prior to getting the hitachi, I used a dremel with a router base. I wasn't trilled with it since it lacked power and the base was flat.

I remember that Les did some pretty arched backs on his ukuleles. His construction was real thin & light with only as much bracing as needed. I'm sure that the 'thinness' of his backs allows for easier bending of that back shape. I don't remember the exact thickness, but I think he was somewhere around .05" to .055"

Owen

Title: Re: Radius on soundboard and back
Post by ukeman on Aug 4th, 2005 at 2:47pm
Aloha Guys!

I like to dome my guitars and 'ukuleles and your joint connections will all be positive provided that you use a domed workboard matching the desired radius of your selected plate. Make several! Use one radiused workboard with sandpaper, you can buy sanding discs up to 24 inches in diameter for use with industrial floor sanders, mount one of these on your workboard.

Pre radius all bracings on your domed workboard.

Glue-up all bracings with your plate on a dome workboard.

Sand your sides and ribbed linings (tentalones) with the domed workboard, prior to plate attachment, while sides are still in your holding form.

Glue-up plates with the domed board as a caul...a washer of the intrument shape..oversized out of floor carpet foam underlayment is cool twixt plate and caul.

Do all of these steps and the fit of your plates will be nice and true and the integrity of the radius intact!

OK all, dome away!   laters  ukeman

ps...main thing is your radius dishes are made accurate.

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