Official Luthiers Forum!

Hi all,

I'm new to the forum and this is my first post. I hope I'm not asking a tremendously silly question... but here we go.

I will attempt in a month or so my first acoustic guitar build from scratch (to be fair it will be the overall second, I'm working on a kit now). Since it will be a gift, I have decided to attempt the plan on this website "http://liutaiomottola.com/instruments/Ipomoea.htm".

Ok, the cutaway seems scary enough, not to mention the side bending, but I'm quite confident. Well, confident is a big word... let's say that I will practice with some scrap and I'll take my time. I'll be fine...

Anyway, there's one thing that it's not clear to me just yet: the sides shaping.

The available plan doesn't have the sides profile, so I'm a bit worried... how am I supposed to get the right back angle if I am not sure of how the sides are shaped before bending them?

Is there a way to derive the shape of the sides from the plan and I just don't know how?

If you have any suggestions, please

Thanks!

PS: I already have the woods, I managed to get my hands on what seems to be decent spruce for the top and mahogany for the sides and back... which is not as hard as rosewood => easier to bend?

Rosewood is easier to bend than mahogany...

Seconding, rosewood is way, way easier, especially for a beginner. So, if you use the mahogany and it doesn't work, don't give up.

I think you need something to measure off of to pre cut the profile. Whether it be a plan or a finished guitar of the same. If you don't it's not a big deal. Bend the sides cut to the widest point, the tail. You can put the taper in after it is bent with a hand plane, spoke shave, or a few power sander options that you might not want to try unless you feel pretty confident. Get it close and when you glue the heel and tail block in you can get it to what you want in a radius dish. Hope that helps.

nekran82: Not sure if you are building steel or classical. I build steel so will speak a bit from that point of view. My sides are not formed before bending, and does not happen till after the heel and tail blocks are glued in place. Plan should give heights at both the heel and tail block positions plus a radius for the braces and the overall back. Knowing this the sides are roughed out on the back in the mold and then a radius disc surfaced with abrasive is used to refine the shape. Kerfed lining is glued on and then the disc is used to finish the shape.
Tom

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A person who has never made a mistake has never made anything!!!

What Tom said. Myself, I'm leery of pre-profiling a side. What if I put the waist bend in slightly the wrong place? It always seemed obvious to me that you would glue up the sides, tail and neck blocks and then profile the sides according to the target radius, with heel and tail depths as the controls.

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Jim Kirby
kirby@udel.edu

I profile the sides before bending, but I don't know of anyone else that does it that way.
I do a lot of 3d geometry to determine the exact profile. I wouldn't recommend the method to anyone else, but it works for me. The sides have to be precisely located in the bender, and the neck and tail blocks can be tricky to get exactly right, but you don't need radius dishes.

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A man hears what he wants to hear, and disreguards the rest. Paul Simon

I also usually rough profile before bending, but it's definitely not exact. My process:
-First I draw a center line and locate where along the length of the sides the heel, butt, and waist will be.
-Next I add 1/4" to the heel and tail widths (this gives 1/8" wiggle room on each half), then draw lines connecting them as if there were no radius or side curvature.
-Then I add 1/8-3/16" (depending on the top or back radius) to the width at the waist and connect that to the heel and butt. The smaller the radius, the larger this number will be... for a truly flat top it would be close to 0. As an example, a guitar with 3-3/4" heel and 4-3/4" tail would look something like this:

-Finally cut out the outside rough profile on the bandsaw and bend.

It's not exact and completely unnecessary if you don't mind profiling after the sides are bent and the heel and tail blocks are glued, but I find it gets things reasonably close and it saves me some time, especially for figured woods that are a lot easier to profile using a bandsaw then a block plane.

If you want to profile your sides after bending Cumpiano & Natelson's book: "guitar making tradition & technology"
shows you how using a block plane.


Sent from my iPhone using Tapatalk 2

I also profile mine a bit before bending. Someone on the OLF showed a picture tutorial that has worked well for me to make a profiling template for a given body shape. As follows (no pictures, sorry):
Use a piece of construction paper or cardboard long enough for the side and the top edge will be straight (no profile).
For the back, I take my inside mold and place it on the (for me) 15 degree radius dish. One side of the dish has 2" painter's tape lining it at it's middle layer (of my 3-layer mold).
A pencil tip is placed through a spacer (mine is a 1 cm square of side cutoff material) that has a hole in the middle just big enough for the pencil lead. This is run over the painter's tape registering off the radius dish. That gives you the radius.
I transfer the tape to my side template giving the appropriate depths for heel and tail and the radius is registered on the template.
I transfer the profile onto the side after jointing the top edge of the side and I cut the profile leaving 1/4" extra.
This saves a lot of block planing when the time comes.
I make a template for each new body shape and then never have to measure again.

I agree with Danny, Tom, Rusty and others that say you can profile after bending and attached to end blocks.

I would,
1. Decide which edge is going to be the top of your book matched sides. Make the top edge flat.
2. Lay them out side by side, top edges together, and mark the center of the waist with a piece of tape.
3. Bend the sides
4. Attach to neck and tail blocks keeping the top edge flat. True the top edge up if needed with a sanding board and plane.
5. Profile the sides using one of the various methods. Cumpiano's is good.
6. Make a paper side profile from the side you profiled. You can use it for other guitars made from the same plan.

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Joe Beaver
Maker of Sawdust

If you really want a side profile.....
Take a length of string and mark along the length at 1" intervals or so. Use string that isn't too stretchy
Tape the string around the profile of the body
Measure the body profile depth on the plan at each mark on the string and write it down.....the plans will have to show a top view and side view lined up side by side for this to work. (looks like your plans are ok)
Take the string off and tape it to the side. Mark the depths along the side and connect the dots

But I would still prefer to taper the sides after bending and gluing in the blocks

Just curious... you folks that like to profile after, how do you remove the large bulk of material? Just the radius disk? That would seem to take a long time. I profile before I bend, and I get all the concerns, but I still use the radius dish to get the kerfed lining nicely sloped. However, if there is a simple way of profiling after (other than the radius dish) I'm interested.

Mike:
I use a block plane. One does have to be careful to go with the grain since the material (sides) are so thin.
Tom

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A person who has never made a mistake has never made anything!!!

It goes pretty quick with a block plane.

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Joe Beaver
Maker of Sawdust

Would one of you mind posting a picture of your block planes? I don't get the grain issue. How could you go against? Unless you mean to not go with the grain that is "diving" into the wood. I can see that, you might grab too much. Do you premark before bend or just lay the template on afterwards?

I use the method well described by RM Mottola. It may seem confusing at first but once you get your brain around the idea it is a very simple and quick approach.http://liutaiomottola.com/construction/Ribs.htm#mozTocId690200

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Doug

Don't let fear or common sense stop you from trying to build something

My Lee Valley low angle block plane...the one on the right.

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Doug

Don't let fear or common sense stop you from trying to build something

block plane - oops, someone already said that

I often use the Lee Valley apron plane for this. I really like that plane - it's a little bit more like a palm plane in terms of mass and how much space it takes in your hand, but like a block plane in terms of working towards a flat surface. Very easy to use for a long time.

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Jim Kirby
kirby@udel.edu

That's a nice looking plane! I don't have anything like that in my shop. I'm kind of leaning towards this concept. I've struggled too much in the past with issues arising from performing. So I'm guessing that you mark up the profile afterwards.

Also, do u use the block plane on the blocks too? Or do u cut them closer to final size before gluing?

I cut my blocks about 1/32 oversized and they get sanded down in the sandpaper lined radius dishes.

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Doug

Don't let fear or common sense stop you from trying to build something

I use a spokeshave to get it near, then the dish to fettle it!

I just tried it both ways. One preprofiled and the other after. They way I did it after was just as simple with a plane. What they are talking about with the grain is that the wood planes easier one way than the other. So when you go against it, it's going to eat into it.

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久保
美智え

I posted this method here many years ago, very simple, very accurate and a match for your individual moulds and dishes.

viewtopic.php?f=10102&t=8117&hilit=side+profile

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Hey Colin…YOU'RE the one who's technique I was trying to describe above. Glad you chimed in so I could thank you for the wonderful tutorial. I've been doing it this way with each new body style and love it! It leaves just a small amount of planing to do and, all though I love using my LN apron plane, I don't like sharpening….you're the BOMB!