Best way to curve the back of uke so it has varying depth from lower to upper bouts

Matt Clara

Matt Clara

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Ok, I'm not describing that very well, but perhaps you know what I mean; where most ukes will have sides that are flat where they attach to the top, but curved where they attach to the back, so that the uke has greater volume in the lower bout than it does in the upper. My Hana Lima manual/plan calls for me to cut the shape of the sides before hand, and then bend them, very precisely, so that all the curves end up symmetrical. So far I've a) made my ukes flat, and b) not cut my sides to length until after I've bent them (like that rapscallion dave_g does in his videos).

I figured I'd give it a try the Hana Lima Ia way (though my mold doesn't fit their plans, so I'll have to come up with my own side schematic), but before I do I thought I'd ask, how do you guys go about it?
 
DSCF2254.jpg
Matt I'm in the process of finishing a hanalima and it worked out very well. I think some of the guys use a radius dish with sand paper to do the same thing
 
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I make the taper after bending. I'm not sure I could bend at the correct locations accurately enough. I just install the blocks and cut the taper with a chisel making a nice fair curve by eye. I use a level across both sides to make sure the taper is the same left and right.
To make the drawing you'd have to start with a drawing of the taperred body, side and back plans Then measure how tall the side is at several locations and transfer that to the unbent piece.....
Say the side at neck joint end is 2.5" tall. The neck joint is the zero point on your new side drawing. The upper bought is maybe 4" from the joint (measured along the side arc of the back plan) and 2.75" tall on the side plan, The waist is 8" from the joint and 2.9" tall, etc...etc. A few more points and you can make a drawing.
 
Matt, do you use an outside form and a radius dish to build your instruments? If you do, here is a simple way to find the profile of the sides before bending.

http://luthiersforum.com/forum/viewtopic.php?f=10102&t=8117&hilit=side+template

I do it this way and it works perfectly. I trim the sides to the profile while still flat, leaving about 1/32" outside the line. After they are bent and held in the mould they only need a few rubs on the sandpaper in the radius dish to clean up.

I recently made an acoustic bass with a body that was not only shallower at the heel block than at the tail block, but was also wedge shaped, i.e. 4"3/4 deep on the bass side and 6" deep on the treble. I used this method to trace the side profiles and they looked like this:
Acbass101.jpg


This is what the sides looked like in the mould.
Acbass139.jpg


This is a pretty extreme case but you can see how much I would have had to trim off the sides if I hadn't profiled them before bending.
 
Matt Clara said:
Ok, I'm not describing that very well, but perhaps you know what I mean; where most ukes will have sides that are flat where they attach to the top, but curved where they attach to the back, so that the uke has greater volume in the lower bout than it does in the upper. My Hana Lima manual/plan calls for me to cut the shape of the sides before hand, and then bend them, very precisely, so that all the curves end up symmetrical. So far I've a) made my ukes flat, and b) not cut my sides to length until after I've bent them (like that rapscallion dave_g does in his videos).

I figured I'd give it a try the Hana Lima Ia way (though my mold doesn't fit their plans, so I'll have to come up with my own side schematic), but before I do I thought I'd ask, how do you guys go about it?
Click to expand...
Matt; have been studying the Hana plans for about a week now. What bothers me is that it seems to me that the taper cut as drawn would simply end with a very lazy "V" shape at the neck or head block. In other words, it appears to be a straight taper for the last 8 15/16ths of the upper bout.
I guess that could be sanded out but still, one of my many unanswered questions.
So, if you follow this part of the plans, please let me know how it works.
 
This is something we wondered about recently and dediced to taper after bending. It was easy to do and turned out fine. Of course, after doing so you could create a template and then just cut pre-tapered sides for subsequent builds... Just an idea.
 
I've found the best way to get the radiius is to cut the shape from a pattern, bend the sides, clamp them into your mold and sand it on your radiius dish, as has been mentioned earlier. The pattern can be a trial and error affair or it can be traced from and existing ukulele that will work for you. You can by radiius dishes to suit your needs or make them yourself. There are various ways to use a radiius dish, I use a potter's wheel for the purpose. And while many ukuleles are indeed built with a flat top, I think you'll find that many of the better ones have a raiius built into the tops as well. In my case I use a 25' radiius for the top but unlike the back, which is a 15' bowl type radiius, the arc on the tops are sprung in one direction only, from side to side. The tops of the sides are sanded in the same manner as the backs but on a radiius board, not a dish, and is done by hand. A top with a slight radiius in it is MUCH stronger than one than is flat and it allows you to get by with the tops being a little thinner. Naturally, you'll need to radiius the bridge in order to get a proper fit. When building with radiiuses it's also necessary to have radiiused work boards for your tops and backs.
I have a suspicion I am not explaining this well. Maybe Pete will post a video :)
I'm off the computer for a while since the jungle claimed mine.
 
Moore Bettah Ukuleles said:
I've found the best way to get the radiius is to cut the shape from a pattern, bend the sides, clamp them into your mold and sand it on your radiius dish, as has been mentioned earlier. The pattern can be a trial and error affair or it can be traced from and existing ukulele that will work for you. You can by radiius dishes to suit your needs or make them yourself. There are various ways to use a radiius dish, I use a potter's wheel for the purpose. And while many ukuleles are indeed built with a flat top, I think you'll find that many of the better ones have a raiius built into the tops as well. In my case I use a 25' radiius for the top but unlike the back, which is a 15' bowl type radiius, the arc on the tops are sprung in one direction only, from side to side. The tops of the sides are sanded in the same manner as the backs but on a radiius board, not a dish, and is done by hand. A top with a slight radiius in it is MUCH stronger than one than is flat and it allows you to get by with the tops being a little thinner. Naturally, you'll need to radiius the bridge in order to get a proper fit. When building with radiiuses it's also necessary to have radiiused work boards for your tops and backs.
I have a suspicion I am not explaining this well. Maybe Pete will post a video :)
I'm off the computer for a while since the jungle claimed mine.
Click to expand...

I get what you're saying--in fact yours makes the most sense to my easily confused mind..
 
Moore Bettah Ukuleles said:
I've found the best way to get the radiius is to cut the shape from a pattern, bend the sides, clamp them into your mold and sand it on your radiius dish, as has been mentioned earlier. The pattern can be a trial and error affair or it can be traced from and existing ukulele that will work for you. You can by radiius dishes to suit your needs or make them yourself. There are various ways to use a radiius dish, I use a potter's wheel for the purpose. And while many ukuleles are indeed built with a flat top, I think you'll find that many of the better ones have a raiius built into the tops as well. In my case I use a 25' radiius for the top but unlike the back, which is a 15' bowl type radiius, the arc on the tops are sprung in one direction only, from side to side. The tops of the sides are sanded in the same manner as the backs but on a radiius board, not a dish, and is done by hand. A top with a slight radiius in it is MUCH stronger than one than is flat and it allows you to get by with the tops being a little thinner. Naturally, you'll need to radiius the bridge in order to get a proper fit. When building with radiiuses it's also necessary to have radiiused work boards for your tops and backs.
I have a suspicion I am not explaining this well. Maybe Pete will post a video :)
I'm off the computer for a while since the jungle claimed mine.
Click to expand...

Chuck described this a while back and this is how I've been doing it since. I've never built a flat top. I'd be happy to post some pics of the stuff I use to do it if you want, Matt.
 
The Hana Lima plans do not call for a radius as there is no curve at all along the horizontal (side to side) axis. Instead, two planes comprise the vertical (neck to tail) axis, peaking at a point an inch or so below the waist. IIRC, the peak is 3" tall and the neck and tail are 2.75" tall, so the profile is just a gentle slope up and down in straight lines. Should be easy enough to get the back to bend enough just by clamping firmly during glue-up. I tapered the sides before I bent them last weekend, and I hope to be gluing the top and back this weekend; I'll post here if I run into anything unexpected.

I thought it interesting that, unlike the less complicated Stew-Mac kit, the Hana Lima kit did not call for a horizontal curve along the back.
 
On my first attempt at radiusing the back, I sanded it on a 15' dish after having installed the linings. Unfortunately, the linings were sanded too thin in the process just aft of the waist so when I cut for the binding I ended up completely removing the remaining lining in about a 1.5" strip. It wasn't possible to add new lining in that area, so I had to carefully glue in the binding and have it bridge the gap and act as the lining. Next time, I went with larger lining. Does anyone sand without the lining installed or do you allow for the radius when you glue it in.

Andrew
 
Please know that any of these kits are beginners kits. They are a jumping off point for you to practice your skills on. They will produce a good instrument but don't expect the plans or materials to yield you the best ukulele ever made. That's where your creativity and talent come into play. After you've built a few basic ukes you'll learn new techniques and designs to try. I am constantly changing things in an effort to build the best ukulele I can.
Here's the deal on sanding the radiius curve on either the top or back. The sides are first sanded without any kerfing or lining installed. This is going to give you a curve that is very close to your final shape. After the kerfing or lining is glued in, the sides are put back into the mold, clamped, then sanded again. So, to be clear, I sand the sides before AND after gluing the kerfings in. With my method of construction (yours may vary) I glue the tops on while the sides are clamped into the mold. When it comes time to glue the back on I will hit it again on the radiius dish just in case the profile has changed a bit after installing the top.
Just the way I do things.
 
Moore Bettah Ukuleles said:
Here's the deal on sanding the radiius curve on either the top or back. The sides are first sanded without any kerfing or lining installed. This is going to give you a curve that is very close to your final shape. After the kerfing or lining is glued in, the sides are put back into the mold, clamped, then sanded again. So, to be clear, I sand the sides before AND after gluing the kerfings in.
Click to expand...

Moore Bettah's method is something like what I was taught for guitar construction.

The 1st time I put the sides in the radius dish, I run a pencil around the sides. Then I plane done to the pencil line. They now have a close fit.

Then chalk is rubbed on the radius dish. The sides are rubbed on the radius dish. any edges with chalk are planed. This is repeated until the entire edge is evenly chalked to indicate that it matches the dish.

The teleróns are glued in slightly proud of the sides. Then a block plane is used to get the teleróns level with the edge of the sides.
Then the chalk process in the dish is repeated.

You could also make a radius "stick" to sand down the sides like this:
http://www.mimf.com/cgi-bin/WebX?13@18.nJB5aXrzF7e.0@.2cb6b96b/42

You also should have a radius curve on your braces.
 
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