How to make a Radius Dish

Dave; Thank you. This is a great post and very helpful.
My question now is, in what situations would you want to only have the arch in one direction?
My assumption here is that the domed radius is stronger in all directions where the second fixture you describe puts strength in only one axis.
Make any sense? The second method looks a lot simpler.
 
fahrner said:
in what situations would you want to only have the arch in one direction?
My assumption here is that the domed radius is stronger in all directions where the second fixture you describe puts strength in only one axis.
Click to expand...

Well, I suppose that the arched top puts the strength in the direction that the strings are pulling. I'm no expert, I haven't made enough instruments yet, but from what I've seen and read on various forums some top luthiers use this method (Howard Klepper, Stephan Sobell...) I believe Chuck makes arched tops (I'm not sure 'arched' is the right word) and I'm sure he could explain why better than I can.
Then there are the guys who break the rules and make perfectly flat tops. People like Jim Olson who makes James Taylor's guitars. (A standard JT signature model, he's only making 80, will cost you $15,000. The 20 more expensive special models have already been sold!)

fahrner said:
The second method looks a lot simpler.
Click to expand...

The sanding board/trough-thingy is a bit simpler to make. Basically a support at each edge and a row of screws down the middle. What's not so simple is sanding the braces. In fact, I made a sort of simple sled to which I attached the braces and slid it along the board a few times.
 
Dave Higham said:
Well, I suppose that the arched top puts the strength in the direction that the strings are pulling. I'm no expert, I haven't made enough instruments yet, but from what I've seen and read on various forums some top luthiers use this method (Howard Klepper, Stephan Sobell...) I believe Chuck makes arched tops (I'm not sure 'arched' is the right word) and I'm sure he could explain why better than I can.
Then there are the guys who break the rules and make perfectly flat tops. People like Jim Olson who makes James Taylor's guitars. (A standard JT signature model, he's only making 80, will cost you $15,000. The 20 more expensive special models have already been sold!)



The sanding board/trough-thingy is a bit simpler to make. Basically a support at each edge and a row of screws down the middle. What's not so simple is sanding the braces. In fact, I made a sort of simple sled to which I attached the braces and slid it along the board a few times.
Click to expand...
Thanks Dave.
Re; making braces; have you seen the jig that holds the brace to the intended radius? You cut whats hanging out straight like on a table saw. When you release the clamp, the brace straightens out and the side you have cut straight now has the radius.
tough to explain quickly. If this makes no sense, I can find the link.
 
Yes, I have seen those jigs. I don't think they'd work for ukulele braces, they are too short and stiff. Actually, that jig will cut a spline curve too, but for curves in the order of 25' rad the difference between a spline and an arc is so small thet it doesn't much matter.
 
Well, I'll let you know. hehheh.
Seemed better (more accurate) than trying to do it by hand in a dish.
If it doesn't work I'll turn it into a neck for a frankenuke.
 
Excellent dish design and tutorial Dave. Much appreciated!
 
I had a fair amount of structural engineering coursework in college, but I will admit that part of the braces thing is still a bit of a mystery to (Like where to put them, how thick to make them, how to anchor them into the binding, what shape they have etc). I am glad we have plans for the first few at least. . We spend a lot of time and effort getting the tops very thin so they will vibrate, then we brace them up, so they won't warp like spaghetti. However, the braces do take away some of the ability to vibrate freely. I know the luthiers say building ukuleles is not the same as building guitars, and its certinaly not the same as building bridges, although the science is the same. Its all quite interesting. There is little substitute for experience.
 
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Biiiiig bump on this one; sorry.

Does anyone know if It's possible to use 1/4in plywood for the bent section of this design? I've got almost a whole sheet of pretty good stuff left over from a remodel that's taking up space.
 
I made a 22' radius dish today using this method and it worked out great. The inner circle of spacers calculated to .02331", so I used a piece of venier that mic'd in at .025. I'll make the 12' dish tonight and I will no longer have an excuse for my "flat" builds. Thanks for posting this method, Dave.
 

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I've found that, due to "spring back" in the uke material.. and other things going on with radius dishes... the sanding process... and using it as a "go bar jig" to produce the radius desired....the end product isn't always what you wanted ???....this is cold bending... sometimes it requires a 8' rad dish to produce a 12' rad back piece (type of thing)...so make a couple of metal radius gauges to check the finished results..and adjust the dish to suit, till you get what you are after...or you could design a hot radius jig?????
 
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Good point. A post from several months ago summarized the radii that Chuck (25' front & 15' back), Pete (22' & 12'), and Dominator (20' & 10') use. Thinking about "spring back" and other factors, I chose to shoot straight down the middle with Pete's 22 & 12. This is my first build that isn't flat, so I'm just working it out as I go.

What do you use, Timbuck?
 
Ken W said:
What do you use, Timbuck?
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For fronts I just use a simple jig plate (pinched off Pete)
that raises the bridge area about 1/2 mm ...for the back I use a 10' rad dish to sand the linings area.. and another jigplate at approx: 8' to put a greater than 10' rad on the back...this usualy springs back to about 10' ..sometimes less (depending on the weather)
..I've had domed backs coming off the go-bar deck complete with braces..and an hour later they have reversed and gone dished, just because the sunshine thro' the windows warmed them up a bit...the UK climate can be cruel.
 
arched back and top? You guys are killing me. I just finished building my first pair of ukes by the Hana Lima plans and they stressed getting things flat and I sweated that detail now you are telling me I gotta take it to a whole new level of complexity;)
thanks guys! lol
 
rickmorgan2003 said:
arched back and top? You guys are killing me. I just finished building my first pair of ukes by the Hana Lima plans and they stressed getting things flat and I sweated that detail now you are telling me I gotta take it to a whole new level of complexity;)
thanks guys! lol
Click to expand...

Yep...I know what you mean. It seems like there is always something new to learn and think about.
 
I'm just resurrecting this thread as I just finished a jig to radius my bracing using a router. In the past, I had used my radius sanding dish but thought this would give me better results. I think its pretty self explanatory. This one is for a 15' radius but I am assembling one for a 25' and 12' radius too. I originally thought I'd use both sides of the jig but found it to be so quick and easy that there wasn't any point.

Andrew
 

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I made one too, in under an hour. I love this method!

Here's the base board with all the little bits glued on:

bild-705035.JPG

http://www.argapa.blogspot.com/2011/12/new-radius-dish-part-i.html

And here's the finished dish:

bild-773568.JPG

http://www.argapa.blogspot.com/2011/12/new-radius-dish-part-ii.html

And here's a couple of pics from the one I made in 2008, using the router on a sled method:

image-upload-131-795752.jpe


image-upload-107-765060.jpe


Thanks for this thread.

Sven
 
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