Official Luthiers Forum!

Hi,

Yesterday I finished writing the last part of a topic in a forum. It was about a guitar that I built a couple months ago. I wonder if this may be of interest to you -it's written in Spanish:

http://www.guitarrista.org/2008/forum/v ... 29&t=36808

It doesn't really belong there in that forum (almost no makers), but I wanted to answer some ridiculous comments on CNC being for quick money makers. I wanted to show that there are creative ways of using it.

Best regards.

I don't read spanish but the pics speak for themselves - beautiful work!

There are so many other aspects of making money that it's ridiculous to suggest CNC lets you make a quick buck!

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http://www.PeakeGuitars.com

Fernando

I see you use Rhino as well? Great job on the guitars.

Mike

Yes, I'm using Rhino.

It's a pity that some among you don't read Spanish, but I'm happy if you liked at least the photos -- thanks!

I took Spanish in high school, but that was a long time ago. I do remember some but not enough to converse with you either verbally or with email. I do agree it is a pity. I wish I had taken more higher level classes, and studied harder.

Mike

+1 on the beautiful work comment, there are some gorgeous guitars in those pics!

I think a lot of the snarky comments are due to envy more than anything else. Small people.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Gorgeous work and welcome to the OLF. Hopefully you won't encounter any snarky comments here. And I'm sure we'd all love to see anything else you might be working on.


Bob

Wow! Fabuloso.

I am lucky enough to have been able to read it, and can say that Jaen really has amazing insight. I have two quick questions:

1) I have heard others say you shouldn't carve the braces but glue them in on an acoustic. Have you experimented with both ways? What is your impression on the difference in sound?

2) I noticed that you use a very similar system on the tailpiece as Mauro Marchesini, including the exact same aluminum insert. Is that insert something you are buying at a hardware store, or is that something you cut out of aluminum?

Gracias!

Thank you alll for your comments!

I usually make the braces and glue them the traditional way. However, when either the guitar is small or its top is hard wood, I sometimes carve the braces with the CNC. I make them parallel when the top is soft wood, but I have used curved braces in maple tops like this:



That way the braces go below the bridge posts and they also cover the top at the points where it is wider, in a mixture of parallel and X bracing. I am conscious that the grain does not run along the braces in those curved braces, but I am sure they won't fail, because I do that for sturdy guitars that are going to be used mainly as electric instruments.

If the top is small, carved braces are not necessary (no wide bout to support), but I use them when the top has a bridge pickup (that leaves out X-bracing) and there is not room for conventional parallel bracing. I have a model with very little space available under the top, and curved braces are a good solution in that case.

The guitar shown has parallel braces, and it's all advantages. I add a piece of wood to make the braces taller, but it's all flat surfaces, so the contact between both is perfect. The grain runs perfectly parallel. I used the same arrangement for the last guitar of the same model:



(Notice that this one has two small pieces for avoiding the pickup selector switch to rotate when tightened, an improvement over the guitar in the article!)

Now the questions about the tailpiece. In the past I used a simpler tailpiece attachment, a bolt:



One day I received an order from a client who told me he didn't like it. I told him I would think of a solution and I arrived at that design, much cleaner:



In fact, I was already making the big archtop tailpieces with a thinner aluminum piece that was quite similar (except it was bent at an angle for reaching the end pin).

I make these pieces in the CNC:





I bought some end mills for cutting aluminum and they work great with the help of WD40.

This is a really stupid question, but why the wiggly sides? Because you can, and it looks cool?

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

It increases contact area in the direction the strings are pulling on the tailpiece (which greatly lessens the chance that the stress could focus on one point and split the tailpiece). That's my guess and I'm sticking to it

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I can live with that!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Really nice work Fernando. The insides are even more impressive than the outsides.

Would you mind sharing your process for drawing the arched/carved top in Rhino? I didn't quite understand all of the processes from the screen shots.

That's always been a tough one for me.

Thanks, Bob, for the tailpiece shape explanation. I couldn't have done it better!


Sheldon: I will try to explain how I design the top, hopefully a little better than what I did in the Spanish version.

My method begins by making a top very carefully, but only the outside and without a recurve (the depression around the edge). Then I draw a grid on it, measure the height of all the points in the grid with a thickness caliper and then enter them into Rhino, using a grid size of 20 mm. This is the result:



Next I make a Patch that contains all the points in the grid plus the external contour. Then I create a set of horizontal planes every 3 mm and find their intersection with the patch surface:



That includes also the intersection with the plane at elevation 0. Consequently, there are two lines with elevation 0: the contour and the first level curve close to it. You will find many other tiny curves very close to the edge that are artifacts - delete them.

Then I delete the patch and the initial points. From then on, I'll work only with the level curves. I will simplify them, removing many knots (Rhino uses too many) and then I smooth them, carefully, by hand:



When I am satisfied with their smoothness, I build a Patch surface again. This time I won't include the contour in the Patch:



The flat surface around the contour is the surface between the contour and the first level curve, as you can see.

Checking the surface is easier if you use some test planes, finding their intersection with the surface:



Using different angles and illuminations on the surface will help to find irregularities. Graphic packages are good at that, but sometimes you will have to change the illumination to discover a bump. Usually, Mastercam is better than Rhino for finding those irregularities.

This is an iterative procedure. If you find a bump, either reshape some curves or alter the stiffness of the patch, that should be kept as high as possible.

After this, the outside surface is finished. For making the inside, I use an offsetSurface command, at a distance of 6.5 mm from the outside. Depending on the stiffness of the piece of wood, the bracing, the intended use of the instrument and other factors, I will set the router at this distance or less when I route the inside, but this will be at run time. Notice that the thickness will be constant after machining.

The final graduations will be done by carving the inside the top for the central part of it. The recurve will be carved when the soundbox is closed. This way, the central part of the plate outside is not modified, and so the bridge foot and the pickup rings will need very little adjustment to the surface for which they were machined.

Those are some really nice patches. I'm more of a network surface guy but I do use patches to tie things together at the end and fill in small gaps, etc..

Just to show another way to skin the cat, here's a screenshot from an archtop surface that I modeled:


If I remember right, I mainly used the sweep 2 rail command. I setup a very similar "topography" frame when setting up the rails for the sweep command.

Once again, really nice work!

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http://www.PeakeGuitars.com

On my carve top / LP models I start with the side-view curve (the one parallel to the Y axis) and the outlines (XY plane) and build the internal ones (parallel to the X axis) manually. That gives three curves in one direction and a bunch crossing the other way to do a network surface with. I could never get satisfactory results using height contours.



Modeling a PRS is a real exercise in self-loathing (this one isn't technically a PRS, it's a reverse-engineered customer guitar, but it's got a resemblance...)

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Well......you're in luck since that's a lot of what I did when I worked there for a few years. I was pretty much the main guy for all that stuff. Here are a few pointers on the PRS style:

*the tops of the bodies have an area that is more or less flat and is set at what is basically the neck angle (it's actually a bit less than the neck angle). The trem bodies and the stoptail bodies have different angles since the neck angles are set differently on them.
*check out the hand carve area a little more closely - specifically, check out the contour of the hand carve as it exits the profile...this is pretty key to getting that area modeled correctly.

This is nothing you can't tell by just looking at their stuff...so I don't think I'm giving too much away here...!

Other than those two things, it looks like that body has the right idea withe the slight bit of recurve, etc.

I got to work on a couple other shapes while I was there as well. I did a lot of work on the SCJ thinline and the singlecut hollowbody. Fun stuff....but I'm on to greener pastures now...!

Trev

_________________
http://www.PeakeGuitars.com

I am translating it, and I have put it in my web site; it starts here:

http://www.guitarrasjaen.com/English%20 ... Feder1.htm

Sorry -- some of the links above don't show the images now...

Fernando,
As someone who has just acquired a CNC machine and Rhino, I find your stuff TERRIFIC!! I am still in the steep learning curve portion of all of this and look forward to your completed translation and I will be using a lot of it to tutor myself on the use of Rhino and the CNC Machine. So... a big THANKS for doing this !!

Shane

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Canada

Fernando
What Shane says and another dozen wow's!!!
You put a lot of time and effort in the tutorial and it's greatly appreciated.
We "CNC Luthiers" shouldn't have to defend ourselves but you've certainly done an excellent job of showing the place of CNC in luthiery.
I too cannot wait for the rest of your translation.
Very interesting stuff!!!
Nelson

Fernando--I am intrigued by your leaving the braces intact when carving the top and particulary the curved braces. I've asked for opinions on this concept on a couple forums in the past and didn't receive much positive feedback. I believe the main objection is no resistance to splitting the top since the brace grain and plate grain are one and the same.. You mentioned gluing a piece of wood to the top of the braces to strengthen and it looks that like might be a good application for a thin piece of carbon fiber.
I'm surprised that you didn't leave a fillet where the brace meets the plate as it looks like that would add strength. A person could also use a ball end mill to undercut the sides of the braces much like an I-beam to get more strength with less weight. All kinds of fun!
Nelson

Fernando,
Very nice stuff! I need to get over to site now and read the translation.

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Jim Watts
http://jameswattsguitars.com

Thank you all, again!

Nelson,

Your objection to carved braces is quite logical, and I must say that I hadn't thought about that. However, I don't do that construction for every guitar that I make. I use it for smaller archtops, heavier tops (for electric guitars) and hardwood tops (and not always). I wouldn't do it for a light acoustic big guitar. Right now I am making a 18" archtop that will be used as an electric guitar, but I haven't carved the braces in the top. Guess that I would do that for a cheaper guitar. When price is important for the maker and for the player, I think that carving the braces can be a great time and money saver too!

That said, I agree that the problem with the splitting could happen the same if the braces didn't open a lot, i.e., if they were almost parallel to the top grain. This is more or less the case with many guitars and, you're right, it would improve a lot if carbon fiber was used to top the braces. I am not sure if this should be done using two layers at 90º, because carbon fiber doesn't have the same properties along and across (sorry if this is not the case, but I haven't worked with this material), but anyway it is a great idea!