Official Luthiers Forum!

After watching the videos from cyborgcnc on modeling an electric neck, I attempted to apply it to an acoustic - pretty much the same processes apply, but I'm a little stuck on the heel contours...Here is what I did step by step - the problem is that in the end, I wind up with these little ridges on the back of the heel that I cannot seem to get rid of...

first, I laid out the geometry for the profile of the heel, as seen from the back...


Next, I extruded the profile so that it gave me the heel part...


Next, I added a fillet to the extrusion, giving me the shape of the heel...


Next, I added some guide curve geometry, to lay out the shape of the sweep between the neck and heel...


Then, I knit the faces of the extruded heel together, so that I had one surface to loft to...


A little more guide curve geometry..


And finally, a surface loft to create the contour...


As you might say when describing a dream..."Here's where it gets wierd!" - in this next pic you can see the funny contours around the heel - not a smooth transition like I wanted. How do I get rid of those?


I've spent hours on this and its getting frustrating. I cannot seem to get the right combination of guide curves and lofts to make this a smooth contour..

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Mitch

Sandpaper works .


Lars

Two potential solutions:

1. Easiest - reference - so we understand each other - our problem loft begins at the neck and ends somewhere near the heel.

a. Make a new plane .01" from the plane that begins the loft.
b. Copy the drawing that represents the beginning of the loft to this new plane.
c. Create a new loft by grabbing BOTH identical sections at the beginning along with other sections.

This will force a more linear beginning to your loft and MAY provide surfaces more to you liking. Adjust the distance to .02", .05" to see if the result is better or worse.

If it still isn't perfect enough....see the next post.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

2. Harder - but full control.

a. Create a series of planes maybe 1/4" apart from each other from the beginning of the loft section to the end.
b. Use the intersection curve function to create a cross-sectional sketch on each one of these new planes from the "bad" surfaces you are currently unhappy with.
c. For each new sketch...draw a single spline along the geometry and then delete the old lines.
d. In the offending areas reshape the splines to provide Solidworks more information about where you want that surface to be in that local area. Clearly you can't draw symetrical splines so you'll have to manipulate half the spline, mirror it down the middle, and then redraw the whole spline.

Tedious...but this offers precise, artistic control over the generation of a surface that no canned module will ever produce. Simply put, Solidworks doesn't know what you want until you give it information that tells it where to establish your surface. You need more cross-sections or it will revert to it's ignorant habits.

When re-lofting you don't have to use all the new cross-sections you created. When doing this you'll often find there are only one or two new sections that need revision. After you practice this a while you'll be able to spot the pertainent cross-sections and eliminate a LOT of fiddling about. This is a very artistic endeavour when you realize how much control actually you have doing it this way. Even if the easy way worked well enough for you, I recommend exploring this technique.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Thanks Stuart - Just so I'm clear...

I would use the existing guide curves to layout these splines, then delete the guide curves?

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Mitch

If you would like to send me .iges surfaces or a parasolid (v.13) file I could do this for you and send it back as a Solidworks file. I'm using 2001 and have never updated. I can send you my old files but you can't send me .sldprt files.

I think the whole thing will seem much clearer if illustrated.

The basic idea is to use your old loft, make cross-sections from that loft, fix the offending cross-sections, and make a new loft from the revised cross-sections.

Your old loft is hidden and afterwards, only a reference.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I"ll PM you a parasolid

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Mitch

Oops, can't attach a file there...PM me your email address and I'll send it over...

Thanks!

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Mitch

Check your PM

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

You've got Mail!

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Mitch

Ya.....your new loft will be created using ONLY your edited cross-sections but you need your old loft to generate the basic sections.

Read how to make an "intersection curve" from your help file. That's a good place to start while I make you an example. If you do this I think this will all come together for you pretty quick.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Bummer.....can't open it.

Make sure you used the version 13 when saving parasolid files. In the save box after you select parasolid there's a version box below where you can select which version to save to.

If you did that then that's hopeless....so try .iges surfaces in that case.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

There's a version 13 file headed your way...

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Mitch

One more time

I got that one opened but I need the neck AND the old loft that you don't like.

It would be good to include all the heel surfaces too.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

A few intermediate cross spline probably wouldn't hurt, don't add too many though as this brings on it's own set of problems.
Also you need to constrain the surfaces to be tangent to one another.
I'd start by adding tangentcy to the surface, then add cross splines wherever I felt like I needed more control over the surface.
When making cross splines, make sure they're tangent to any surface they interact with.

edit: what version are you running? They added a bunch of surface stuff in 08 or 09. they're surfacing tools are much better than they use to be.

_________________
Jim Watts
http://jameswattsguitars.com

I'm running 2010

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Mitch

Easy fix - there should be one spline that goes from the back corner of the heel to the point where it intersects the fingerboard glue up surface. This spline is highlighted in red in the screenshot above. The model above is from Rhino, but the construction process for both SolidWorks & Rhino is the same in this case. I'm sure there are other ways to do it as well..but this way has worked well for me.

Have fun,
Trev

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http://www.PeakeGuitars.com

Parser is on the right path....

The more "direction" you give to solidworks, the better the outcome. If you give it more curves and information, as in guide curves, the better the result will be, since you are guiding the surface.

Another thought: Instead of using a loft, use the surface patch feature...and compare the outcomes...surface patch is very particular, and likes to have adjacent surfaces, but in many case, it works better that lofting....

let us know the outcome.

also: Send me the solidworks source, and I will take a look at it when i get sometime...

cyborgcnc@gmail.com

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

I've had a different experience with lofting versus the surface patch - I pretty much avoid them whenever I can. You have to mind your P's & Q's when lofting (learn how to set the end conditions - curvature continuous, tangent, etc. when lofting from one surface to the next..and also learn to use guide curves). In the end though, lofts are very controllable. With both Rhino and SW, the key is to figure out how to design the best 3D framework to construct the surfaces from. The only time I've had to use patch surfaces is when doing the last little "puzzle piece" when modeling something like an archtop surface from a point cloud. With that said...if it was something I was designing from scratch, I'd make it so that it lofts nicely...!

Trev

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http://www.PeakeGuitars.com

Check your e-mail for the files I sent, Mitch.

Note that the neck and the heel are created together with a single loft on this through the use of 3D lofting sections.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

A big thank you to everyone who responded (even with the sandpaper suggestion - I was "this close"! ) - and thanks to Stuart and CyborgCNC for spending extra time on this. I have Stuart's files and will try these suggestions to see what works best for what I'm trying to accomplish -

What a great forum!

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Mitch

Very Cool stuff stuff Mitch!

I feel like I'm following in your foot steps.

I'm building a Joe's 4x4 CNC too.
I just finished my first tutorial in Solidworks 2010 a few days ago.
My new Book "SolidWorks 2010 Bible" should arrive Monday.
My first CNC project will be an acoustic guitar neck.

When you finish your CNC and master acoustic necks, what are we doing next?

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Rick Hubka
Chemainus BC Canada

Custom fretboard inlays
bridges
Pool cues
new cabinets for my kitchen


and I'll take a stab at those stepping stones that Joe is perfecting over on his forum - that looks like a money maker!

If you truly are following in my footsteps, watch your step! I feel like I'm walking through a cow pasture blindfolded!

I would highly recommend if you are using Solidworks that you get CyborgCNC's videos. I have learned a tremendous amount from those...

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Mitch

Study how to make 3D stetches and incorporate them into lofts. You can draw complex surfaces many ways in Solidworks and I believe that people naturally think in terms of lofting 2D sketches and 2D guide curves together to form complex surfaces. Learning to understand 3D sketching, however, will make you think in different, more "global" terms. Though it may seem daunting, I would suggest it becomes natural quite quickly and GREATLY facilitates your ability to quickly arrive at a solution.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

ditto what Zlurgh said. The "art" in all of this is being able to look at a part and dissect it into individual lofts, sweeps, etc.. Often times, the way the you model the part reflects how you would hand carve it.

It takes a long time to get to where you can get high quality results consistently..! Just keep practicing...

Trev

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http://www.PeakeGuitars.com