Official Luthiers Forum!

Ok, let's presume I am truly a CAD/CNC neophyte in every respect. Which I am.

I would like to work backward from a set of commercial plans and get ACCURATE drawings into CAD for some of the pieces/parts. Such as a half body mold etc. I have to think that there is an accurate and straight forward way to do this but I have been searching the net etc. and can't find anything helpful.

Thoughts/Suggestions? What do you guys do? I am sure this is not a new problem.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Brock, this isn't really easy, and there is no great way to do it. A lot depends on the quality and accuracy of the initial drawing that you're starting from. (If you have no drawing, then you are measuring a physical object and creating "from scratch" CAD drawings.)

With good drawings, you can scan the drawings and then:
A.) use them as a background layer, and "trace" over them, fitting lines and arcs to get as close as possible to the original. Don't forget to make the endpoint of each segment the beginning point of the next segment.
B.) some CAD software has an "auto-trace" (raster to vector conversion) function built-in and the software will take it's best shot at digitizing the original scanned drawing. If not included in your CAD package, then look for a 3rd party program to do that job, and load the resultant DXF file into your CAD program and start the process of cleaning up what it missed or messed up.

AlgoLab Raster to Vector Conversion Toolkit: http://www.algolab.com/r2v.htm

This Scan2CAD software looks interesting: http://www.softcover.com/

HTH,

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Brock, you recreate the drawing using it's dimensions and you'll have to measure a lot of these on guitar plans.
For a body outline you need to create a set of X Y points (every inch or so) from the drawing for half the guitar, fit a spline through the points and mirror it.
If you want an original design it's easier than recreating an existing body shape IMO as you only need a few key points for the spline to pass through and the just make it look good. The fewer points a spline can pass through the smoother it'll be.

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Jim Watts
http://jameswattsguitars.com

Interesting. Thanks guys. I would have thought there would have been some slick solution to get this nailed.

Most of my guitars are in CAD so that is easy, but this is a classical from commercial plans (which are really nice), but I want to make some of the templates/tools on CNC.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Another way which has worked for me, is to simply take the plan (I have done this with the Stewmac '59 les paul) and simply place it on a flat surface, and take a picture of it with your digital camera.

Now this, will not be the size you need, since it will be scaled down, but one can easily correct this with photoshop, before you bring it into the CAD program. Placing it on a white background will help, but again, you can make corrections in photoshop. Since most of the dimensions are listed on the plan, you can scale it inside the cad package as well. I use solidworks, and it makes this process easy. SW also has a function that will automatically trace the image for you, to create a vector drawing. So no external vector packages required.

You can then scale and size precisely to the drawing dimensions, and continue with extrusions and surfaces. Doing this, the model comes out quite good, and depending on the attention and detail you put into it, very accurate to the drawing.

http://www.cnclutherie.com/lespaul/

(the extra cavity routes in the back are for integrated electronics, and and integrated USB port....)

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-CyborgCNC
http://www.cncguitar.com
https://www.facebook.com/CncGuitar

I've been thinking about posting a tutorial on this exact thing....maybe I'll work one up tonight and post it?

Using any capable CAD package, it takes literally minutes to get a good basic shape with "clean" curves that transition correctly, etc..and making nice curves is the foundation for making nice surfaces...

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http://www.PeakeGuitars.com

That sounds like a good idea to me.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Maybe I'm missing something here.... you say that the guitar has commercial plans? do these include dimensions? and if so, can you not use them to draw your wireframe? By the way, what are you using for cad?

Another hi-buck solution would be to take the guitar to a CMM shop and have them digitize the guitar. Then you could extract wireframe, solids, and surfaces from the model.

Guitar plans aren't usually anywhere near the quality of machinists prints where you can construct the proper shape strictly from the dimensions. They usually include a lot of splines, and the dimensions are more or less for scale on anything that isn't strictly straight lines. So, if you want a good CAD file then you need to do a lot of fiddling around and reverse-engineering of the drawings (and hope that they're relatively accurate as drawn).

I tend to prefer physical samples, so I can go nuts on the accuracy...but that's the machinist in me talking over the luthier

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I've been digitising my designs (to have someone else cut me up some templates - the time for CNC for me lies far in the future, when I have the space to put one) by taking photographs with roughly a 50mm lens (or at least one I know has little to no distortion; i'm anal enough that I let software correct any), then trace over it in a vector graphics programme (inkscape on my mac in this case), and then scale to size using the long dimension after grouping the various elements. I've 'checked' accuracy against hand-drawn plans by opening the files on the computer and displaying them on my HDTV (40"), which is big enough and bright enough to act as a light box that I can hold the original drawings up to. Smaller things (headstocks, bridges) I just print or check on the laptop screen.

Sorry if this has already been said- I didn't read every detail of every post...
Some blueprint houses have wide format scanners that are pretty accurate. There are limitations- paper shrinks, stretches, etc, and the scanner has to be able to output a file that your cad software can read into an editable form (bitmapped images are useless for cam).
Short of that, I usually take whatever I'm using as a master (plan, tracing, etc) and divide it into 1" grids, plot the entry and exit points and set a matching grid on your cad drawing. Print drafts onto vellum that you can lay over your original to see if you're accurate or not.
Short of all that maybe a local college architecture student would moonlight it for you. Those kids are scary fast in Autocad...
-C

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Freeborn Guitars
and home of BeauGuard©

Brock,

I have been drawing CAD guitar plans for one of my clients.
They are in the simplest format drawn with AutoCad Lt to full scale (no scanned images).
Most importantly, the guitar body shape is a continuous unbroken line in the proper color which my client uses to send directly to his laser cutter.

Rick

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Rickey
http://www.cadguitarplans.com

please allow me to further explain what I do.
Basically I redraw the guitar in AutoCad from the beginning. I usually research other plans, pictures, guitar manufacturers and actually borrow guitars from my friends to get specific dimensions.
I then begin by first drawing the guitar body which takes me about and hour or two to get it just right with arcs and then combining them with the pedit command to make it a continuous line.
I consider the body shape the foundation and I sort of build the guitar from that point on by adding all the necessary features that make a guitar.
It usually takes me about 14 hours to complete a full scale plan.

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Rickey
http://www.cadguitarplans.com