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backwoodsmark
01-02-2014, 06:22 PM
Hi everyone. Does any one arch the tops on your ukes? I have a 25 ft radius sanding dish for guitar work. I build mainly baritone ukes (tuned GCEA), but build tenors also. I wondered if the crowned top gets too stiff and would affect the sound? My flat tops always seem to sink a little in the center. Humidity is a problem as usual.

Moore Bettah Ukuleles
01-02-2014, 08:18 PM
25' for the top,15' for the back. Works for me.

ukulian
01-02-2014, 09:16 PM
20' top and bottom

dmecha1012
01-03-2014, 01:33 AM
25' for the top,15' for the back. Works for me.

Do you use those same figures for all size ukes ?

mzuch
01-03-2014, 03:30 AM
My tenors and baritones have a 15' radius on the back and 28' on the top.

rudy
01-03-2014, 10:45 AM
Twenty top and bottom for me. It's a whole lot easier if you only have to make a single radius form and I don't think the benefits of two diverse radii are really worth the effort.

The radius I used for the tenor built here is 20':

http://www.bluestemstrings.com/pageUke1.html

There's a video clip that demos the sound, and I think it sounds fine. (As much as YouTube can convey, anyhow.)

Moore Bettah Ukuleles
01-03-2014, 11:20 AM
My radius dishes are cylindrical for the top, spherical for the back. Hence the reason for two.

ukulian
01-04-2014, 09:56 AM
My radius dishes are cylindrical for the top, spherical for the back. Hence the reason for two.

Does that ease the setup of the neck angle Chuck?

backwoodsmark
01-04-2014, 05:50 PM
This is far out. Thanks everyone for talking about top radius's. I learned something new about cylindrical and spherical dishes. what are they? anyway I'm going to arch the top and back on the baritone im building now. That neck angle is tricky though.

Moore Bettah Ukuleles
01-04-2014, 07:42 PM
Does that ease the setup of the neck angle Chuck?

Exactly. Puts the neck and the upper bout on the same plane.

backwoodsmark
01-08-2014, 08:15 PM
Hi Chuck. I had never heard of a cylindrical radius dish. Can you explain what it is?

Sven
01-08-2014, 09:23 PM
Think halfpipe. Then think 1/32 pipe.

Kōāpaa
01-08-2014, 09:29 PM
Hi everyone. Does any one arch the tops on your ukes? I have a 25 ft radius sanding dish for guitar work. I build mainly baritone ukes (tuned GCEA), but build tenors also. I wondered if the crowned top gets too stiff and would affect the sound? My flat tops always seem to sink a little in the center. Humidity is a problem as usual.

Hey backwoodsmark,
I have a related question. When you say your flat tops "seem to sink a little in the center" are you talking about between the bridge and soundhole? If this is the problem you are trying to address with the arching you might want to also consider your GCEA tuning on the Baritone. Most of the Baritones I have seen are tuned lower (DGBE). The higher string tension (higher frequencies and longer scale length) may be pushing the limits of the design if this is in fact what you mean about the "sinking in the center". My apologies if I misunderstood your statement but I just wanted to throw another idea out there to fix the problem of the center sinking.

Bruce Sexauer
01-09-2014, 05:38 AM
I arch using the same dishes as my guitars, so far. My tops are between 40 and 50 feet, and by backs are 18 feet. I make my own dishes.

backwoodsmark
01-12-2014, 09:52 PM
The tops on both the tenor and the baritone tops sink some after putting the finish on. This is before they have the bridge and strings are attached. So far I haven't had any tops sink between the bridge and the soundhole after stringing up at least on the ukes. Ive had that problem on steel string guitars. Thanks for bringing that up though. Now I know I have higher string tension on my baritones so I will keep an eye on that. I loved the sound of the baritones tuned GCEA so much I feel disappointed when I play a tenor. Guess i'll have to work on getting a richer sound from the tenors.

Michael N.
01-12-2014, 10:38 PM
All true flat tops (i.e. made without a dome) will sink a little across the width. That's even without any string tension ever being applied to the soundboard. They sink and seldom recover irrespective of humidity changes. The good news is that the sinking is extremely slight and does not adversely affect the instrument.
Distortion due to string tension affects both true flat tops and those that are domed.
I don't make Ukuleles but I have done a number of baritone sized 6 strings - extremely small Guitars, correctly known as Chitarra bambini (rather than Guitalele!) . I don't really see the point in doing any doming/crowning on such a small instrument.

rudy
01-13-2014, 01:49 AM
All true flat tops (i.e. made without a dome) will sink a little across the width. That's even without any string tension ever being applied to the soundboard. They sink and seldom recover irrespective of humidity changes. The good news is that the sinking is extremely slight and does not adversely affect the instrument.
Distortion due to string tension affects both true flat tops and those that are domed.
I don't make Ukuleles but I have done a number of baritone sized 6 strings - extremely small Guitars, correctly known as Chitarra bambini (rather than Guitalele!) . I don't really see the point in doing any doming/crowning on such a small instrument.

Another point to consider is that truly flat surfaces often exhibit the optical illusion of concavity where none exists. It's not as much of an issue on smaller instruments like the uke family, but acoustic guitar makers have long been aware of it. It's one of the reasons cited for inducing an arch in the top surface; it does double-duty by eliminating that optical illusion and providing a bit of "wiggle room" for top deflection under string tension. If you know a top is going to deflect slightly under string tension then it just seems prudent that you would accommodate that when building any instrument that has a top (or back) large enough where concavity (illusion or otherwise) would be noticable.

Michael N.
01-13-2014, 01:00 PM
I've heard about the concavity and the optical illusion too. I don't see it though! I'd say that 75% of the instruments that I make are true flat tops and I can honestly say that the concavity thing seems to be greatly exaggerated. Don't forget that prior to about 1850 virtually all Guitars were made with a flat Top and flat Back.

Moore Bettah Ukuleles
01-13-2014, 02:09 PM
If there is absolutely no distortion at all in the top under string tension I feel the instrument is probably overbuilt. It's another of those fine line we've got to walk.

backwoodsmark
01-13-2014, 06:31 PM
another thing to think about is the customers (if you have some) reaction to seeing a even a slightly sunken top. musicians know to look for a "bellied up" top where its sunk ahead of the bridge and bowed up behind. guitars mostly. there's a lot of things to explain to people.

Kent Chasson
01-13-2014, 07:23 PM
If there is absolutely no distortion at all in the top under string tension I feel the instrument is probably overbuilt. .....

Totally agree. I've never had a problem explaining deformation to clients. People buying handmade instruments seem to understand. Before I built my first batch of ukes, I went to a friend's house who has a nice collection so I could look and listen to as many as possible before building. The one that sounded the best also had the most deformation and I doubt it was a coincidence.

rudy
01-14-2014, 03:56 AM
To me that's one of the most important aspects of top arching, to give top deformation something to work with.

If you start with top arching then a small amount of deformation still results in a top that doesn't exhibit dipping above the bridge and a protruding belly. You still get approximately the same sonic results of a lightly braced top combined with a top that doesn't look like it's damaged goods.