PDA

View Full Version : Tapering the Back: Full Body Taper or Upper Bout Only?



sequoia
12-30-2014, 09:16 AM
I'm getting ready to glue in some linings this morning when I had a thought. On all my previous builds I end the taper somewhat south of the waist leaving most of the lower bout sides flush with the lining. Why? I dunno. I guess I always saw the two bouts as independent sections and I wanted maximum height in the lower bout. (My taper is about 3/16"+ (or about 6mm) at the head block running out at the waist.)

So I've been doing some research and went to the classical guitar builders and discovered that they tend to end the taper just where the lower top brace meets the sides. Sort of like I've been doing. Yet, from what I can see, ukulele builders taper in a gradual curve all the way from the head block to the tail block. Now I'm wondering. Is there any consensus on this tapering business?

Beau Hannam Ukuleles
12-30-2014, 09:32 AM
I just make my butts about 3"-3 1/8" and the headblock about 2 1/2"- 2 3/4" then sand the 15 foot radius on a dish

Beau Hannam Ukuleles
12-30-2014, 09:34 AM
oh- are you talking about the top?

lately, ive been sanding the whole top on a 28 foot radius dish, then flip the dish over which is flat and has 100 grit sandpaper on it and i sand the upper bout flat.- this only takes a few strokes

DennisK
12-30-2014, 09:57 AM
I use a flat perimeter for the soundboard, and roughly spherical for the back (in addition to the taper). First get it to a straight taper from tail to neck, but with the sides about 1/16" to 1/8" taller than final. Should be able to lay flat on the bench with no gaps. If you have a radius dish, then glue the linings, and sand in the dish until you have scratches everywhere. The waist should end up a bit higher than the heel/tail.

If you don't have a radius dish, then shave by hand with a finger plane at the heel/tail down to the final height, and smoothly blend toward the waist, which remains 1/16" to 1/8" higher (depending on how heavily arched your back braces are). Glue linings, level them to the sides, and go over it with a fairly small flat sanding block to eliminate any irregularities.

sequoia
12-30-2014, 03:26 PM
oh- are you talking about the top?

No Beau, I'm actually talking about the sides sloping to give the instrument an overall subtle taper. No radiuses involved here although my backs are radiused it doesn't enter the equation. I'm actually talking about sloping sides with a 3/16 inch/1 foot slope... Anyway, I did a constant slope tail to head block and not like the classical guitar builders who might just taper the upper bout. It all becomes a bit arcane really and I don't even claim to understand, but it is important to how the instrument sounds. That we know.

Matt Clara
12-30-2014, 04:32 PM
No Beau, I'm actually talking about the sides sloping to give the instrument an overall subtle taper. No radiuses involved here although my backs are radiused it doesn't enter the equation. I'm actually talking about sloping sides with a 3/16 inch/1 foot slope... Anyway, I did a constant slope tail to head block and not like the classical guitar builders who might just taper the upper bout. It all becomes a bit arcane really and I don't even claim to understand, but it is important to how the instrument sounds. That we know.

I believe Beau mentions that, too, when he says his head block is 2 1/2" (or so) and his tail block is 3" (or so). Then he sands a radius into it. I honestly don't know why one would bother with the tapered body shape. It's not any easier to hold, it doesn't sound any better, it just seems to be a thing that some manufacturers have done, so we do it, too. By all means, correct me if I'm wrong.

sequoia
12-30-2014, 05:23 PM
Matt, that is a great point. When I wrote earlier, "...it is important to how the instrument sounds. That we know."... I immediately thought, oh yeah ukulele boy, how do you know that? I have to admit: I dunno. It is another design element that is part of the Great Central Dogma: "That is how it is done and has always been done as long as I know so that is how I'm going to do it whether or not I have a shred of evidence that it actually makes the instrument sound better/look better/structurally better, I'm going to do it anyway." So much of what we know, or think we know, has been handed down until it becomes ingrained. Hey, if Torres did it, I'm gonna do it.

So I researched this tapered body thing a little bit more and here is what I found: Torres incorporated it into his early 19th Century designs. As I'm sure you know, Torres designs blew everything out of the water and we have been copying him ever since. And with good reason, the man knew what he was doing. Torres is the Man... I also checked all of my commercial guitars and all of them are tapered... But here is a thought: The Hawaiian ukulele is not a little classical guitar. It is a different beast. Sometimes I wonder if we don't want to make ukuleles into little four string guitars. I think about this a lot...

DennisK
12-30-2014, 07:23 PM
I know at least one guitar builder who believes un-tapered boxes sound better. I do it more for appearance than anything. The whole instrument tapers toward the headstock, and it just looks wrong to me if the box depth doesn't follow suit. Also as a carry-over from guitars (which are my main instrument), because it does make the box feel shallower and more comfortable to hold in that case. But I don't think it's a make-or-break feature when it comes to tone.

Timbuck
12-30-2014, 09:18 PM
Being a good engineer ..I do it, co's it's in the spec: and on the drawing :)

Beau Hannam Ukuleles
12-31-2014, 06:47 AM
I believe Beau mentions that, too, when he says his head block is 2 1/2" (or so) and his tail block is 3" (or so). Then he sands a radius into it. I honestly don't know why one would bother with the tapered body shape. It's not any easier to hold, it doesn't sound any better, it just seems to be a thing that some manufacturers have done, so we do it, too. By all means, correct me if I'm wrong.

Yes- i was talking about the sides, AND the radius. Don't do a flat back, they look cheap. I used to teach people how to use a block plane to radius the sides to fit a 15 foot radiused back but it is too hard to explain in writing.

An instrument with equal (or near equal) depth sides from end to head block looks..... wrong.

ModlrMike
12-31-2014, 08:18 AM
Which is better, cutting the taper before you bend the sides, or after? I recon it's probably easier to cut them prior to bending, but it may be technically better to cut them afterwards. Opinions?

Beau Hannam Ukuleles
12-31-2014, 08:38 AM
Id recommend :
1- Sand sides as rectangles
2- Cut rough side shape before you bend.

If you dont have a side template leave rectangle or perhaps just angle them into vaguely triangle shapes to differentiate head from butt. It might be safer to leave as rectangles though if your a first time builder so you have room to experiment with your back shape/radius/taper etcetcetc

sequoia
12-31-2014, 09:02 PM
I take down the sides after they are bent. Put them in the mold and then sand flush to the lowered headblock. It all works out the same and there are many way to skin a cat.

Now, as to a tapered body: It does make a better sounding instrument just like the old masters said. This is old dogma that is based in sound fact and the effect isn't subtle. I've been reading old guitar making books and came across this from some old Spanish dude that has built 10,000 instruments (paraphrasing): "You see what I want to do is kill the upper bout vibrationally. I want an area up there that eats up the sound. Acoustically dead." This seems counter intuitive at first. We worship sustain. But think about it. A symmetrical box that keeps vibrating is not a good thing. Things start sounding muddy. You want the note to come out strong and clear and then die relatively quickly. Otherwise when you are moving on to Em7 the box is still vibrating with Bm7 and that isn't necessarily good. Where these sounds leave the box is in the upper bout with its inclined plane and small chamber.

Does that make sense? Probably not since I just got back from a New Years Eve party. Play on my friends!

Matt Clara
01-01-2015, 03:43 PM
It does make sense, but more for a big, very resonant and loud steel string guitar than for a small, nylon string, can't even hear it over the engine of my idling car ukulele, where half the back of the instrument is pressed up against my chest/upper abdomen.