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Rhino help with Volute area please
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Author:  Bob Hames [ Tue Jul 05, 2011 8:03 am ]
Post subject:  Rhino help with Volute area please
Good Morning

Ok after many, many hours in Rhino I admit defeat.
I have been teaching myself Rhino for a few years now and drawn
up a couple of guitars. I find it a great tool for thinking things through.
While I'm getting reasonably proficient at it, I hit a wall whenever I get
to the volute area. As in the example below, I have been able to produce
a facsimile of what I'm looking for, but to be honest I can't even remember
how I arrived there. Curve network would appear to be the way to go, but
I think I am missing some very basic information.
My goal would be to able to play with the design of this area.

Up until now I've not looked at using CNC, but a good friend has built himself
a CNC (4'x8') and I'd like to try some necks on it, so I'm redrawing my neck with
that purpose in mind.

Trevor's great tute helped me a lot in refining the heel area, but I don't think the
transition at the head applies to my situation (or I'm too dumb to figure out how
to apply it)

Any thoughts or ideas welcomed.

Here's a drawing I did about 2 years ago.
Attachment:
Transition.jpg


I've made quite a few guitars with this design and fairing with hand tools seems
to kind of naturally work out, but I find drawing it a bear!
Attachment:
transition2.jpg


Here's some things I've tried.
As it is required that the curves in the network cross each other, I joined 2 curves
to make it work
Attachment:
Square_a.jpg

The resulting surface mirrored across the centre line
Attachment:
Square_b.jpg


Here I radiused the upper corner.
Attachment:
Round_a.jpg

The result looks better but no idea how to resolve the unfinished part.
Attachment:
Round_b.jpg


I can't help but think that part of what I'm missing is that there's an issue with tangency.
The isocurves in the network are certainly not looking tangent to the neck back.

Help!!!

Cheers
Bob
Author:  Andy Birko [ Tue Jul 05, 2011 10:37 am ]
Post subject:  Re: Rhino help with Volute area please
I'm not really working with Rhino but these things are pretty similar among CAD systems. I'm working on something similar and my strategy is to use a loft with guide curves to keep the tangencies correct and give the right shape. With SolidWorks, it seems that if you mix a curved guide curve with those with angles, it will introduce a "kink" or facet in the lofted surface.

Once I have the swept part done, I'm trying to use boundary surfaces (don't know if that exists in Rhino) to fill in what's left. A boundary surface is basically a surface that is created from the intersection of two curves in direction one and one or two curves in direction two. In the attached pic, you'll see I'm using a loft but it's not giving the results I'd like. I just haven't had the time to do it with the boundary surface yet but I think that's where I'll find my solution.

So, I don't know if this has helped but please post your progress as I think it will help a lot!!!
Author:  Stuart Gort [ Tue Jul 05, 2011 1:30 pm ]
Post subject:  Re: Rhino help with Volute area please
Looks like Rhino lets you make 3D curves so it'll probably let you do this. I have Solidworks which allows me to make 3D drawings from a combination of splines and lines.

There are two tricks here: 1. Break this volute into two symetrical shapes. Or maybe it already is two pieces. I can't tell...but computers certainly get less confused when they have less to assume. 2. Reduce this loft into two loft sections and two guide curves. Since your original shape seems to require 5 drawings you need to combine two of them into one. In the pic you can see one of the white lines representing the loft sections now includes the vertical, straight line defining the end of the volute that you are having trouble with. The red lines are the guide curves.

Try that and see how it goes. This will work in Solidworks though there may be mid loft section required for further control of the definition. Not sure about Rhino.
Author:  Parser [ Tue Jul 05, 2011 1:50 pm ]
Post subject:  Re: Rhino help with Volute area please
The transition to the headstock typically starts at about the 1/2 fret position - not at the nut as you have done it. It looks like the method you chose resulted in smooth, unwrinkled surfaces, so I would stick with that (there are numerous ways to do this). I'd just recommend redrawing that curve at that center bottom of the neck so that it blends into the shank closer to the 1/2 fret position. Also - make sure that all of the curves in the framework that you construct are tangent (or curvature continuous if desired) to the edges & center of the shank of the neck. If your framework is not tangent/curv. cont. then you won't be able to construct a smoothly blended surface. Network surfaces typically work great. Some folks use patch, but I've found that network surfaces are more controllable.

The tutorial I did awhile ago did show a simplistic way to handle the headstock blend surfaces (OK, let's just call it cheating). :D The method in the tute would get you something to carve, but that's about it. You could use a similar method to what is shown in the tute however, and simply trim away the parts that aren't part of your headstock shape. I'm thinking about doing a bunch of tutorials and putting them on my website. I think all this surfacing stuff is one of the high hurdles in doing guitar CNC work.

I hope this helps. Looks good though! Nice looking neck too...!

Best,
Trev
Author:  Bob Hames [ Tue Jul 05, 2011 5:52 pm ]
Post subject:  Re: Rhino help with Volute area please
Hi Guys

Thanks for your informative replies.
We get up real early 'round here and that's my computer time, so I'll
digest all this and get back to you tomorrow!

Ciao
Bob
Author:  Stuart Gort [ Tue Jul 05, 2011 6:19 pm ]
Post subject:  Re: Rhino help with Volute area please
One more thing. See on my pic how that lower white loft sketch has two components, a line and a spline?

On the other loft section, the small, white loft section....you should similarly break that into two pieces, not one continuous spline but two connected splines. The two pieces should have lengths that roughly correspond to the lengths of the lower white drawing. Often, when lofting, the sketches need to have an equal number of line segments or the software will provide a snafu result.
Author:  Stuart Gort [ Tue Jul 05, 2011 6:36 pm ]
Post subject:  Re: Rhino help with Volute area please
AhHa!....when I first replied the top pics didn't load. It appears you already tried it my way except the vertical line segment was included in the upper loft section....which gave you that squareness you clearly don't want.

I actually did a test in Solidworks with that vertical section included as I illustrated and got a good result. Try it my way and I think you'll get a better result than the squared look.
Author:  Andy Birko [ Tue Jul 05, 2011 10:49 pm ]
Post subject:  Re: Rhino help with Volute area please
P.s. I love these threads. The surfacing is really the art part of CNC that not everyone seems to get. For a good laugh, check out the "volute" on the Laguna CNC page.

P.p.s. I think that Stuart's idea is e best candidate so far. Sometimes it's a matter of flipping your mindset 90 degrees and trying again. On the upper part of my scroll, I first did the lofts in one direction and they were really crappy. I then swiched the guide curves and profile curves and voila! I can't believe I forgot about that approach when working on the volute - i know what to try tomorrow now too.
Author:  Stuart Gort [ Tue Jul 05, 2011 11:09 pm ]
Post subject:  Re: Rhino help with Volute area please
Andy Birko wrote:
The surfacing is really the art part of CNC that not everyone seems to get.


I suppose that was true of every new artistic medium. You'll have detractors and critics but the technology won't be uninvented so it can only flourish as an artform as it becomes more and more accesible.

Nobody is going to tell me that after tweaking one spline point a thousand times and viewing a surface from every conceivable angle that I'm not practicing an art. Coming from a long line of artists and musicians, I know art when I'm looking at it. Funny though...my family thought I was a technoboy with this cnc stuff. Then I handed them an instument...and it was fun to watch them adjust their notions. :)
Author:  Bob Hames [ Wed Jul 06, 2011 8:37 am ]
Post subject:  Re: Rhino help with Volute area please
Morning All

Thanks for all the tips and feedback, I'm learning a lot!

There must be some differences between how SW & Rhino handle geometry.
Firstly I'm assuming a controlled loft is similar to whats called a Sweep in
Rhino. You can sweep a number of cross section curves along either 1 or
2 rails.
I tried Stuarts suggestion, but no matter how I try it, I end up with varieties of
the image below. Ensuring the same # of line segments did not help.
Attachment:
Sweep_2rail.jpg


With anything I've tried, the isocurves in the resulting surface never look right to me.
Perhaps driven by what's in my minds eye while I'm shaping by hand, I believe the isocurves
should be tangent to the neck rather than the headstock and not an average of both.

Hope I'm making sense here!
At any rate I'm wondering if I'm trying to force the software to resolve to many lines.

So here's what I'm looking at now.
As per Trevors advice I redrew my lines to begin at the 1/2 fret location.
The top line is tangent to the centerline on the back of the neck, while the bottom one is
tangent to the edge of the neck.
The rail is the edge curve on the end of the neck.
Attachment:
Sweep_1-rail.jpg


This produces this sweep.
Attachment:
Sweep_1-railb.jpg


Another view (and not a good one at that)
It's supposed to show the difference between the shape I had drawn and the
shape that the sweep produced. Hopefully the following pics will make it clear.

Attachment:
Sweep_1-railc.jpg


Here I extended the upper edge of the sweep above the rear surface of the headstock.
Attachment:
Sweep_1-raild.jpg

Attachment:
Sweep_1-raile.jpg

What I'm thinking is to let the sweep define the shape on the back of the headstock so I
"untrimmed" that surface.
Attachment:
Sweep_1-railf.jpg

Attachment:
Sweep_1-railg.jpg

I'm at my max attachments so more to follow.
Author:  Bob Hames [ Wed Jul 06, 2011 8:43 am ]
Post subject:  Re: Rhino help with Volute area please
I'm back!

This is where I stand at the moment.
I'm wondering how much control we have at the top edge of the sweep by tweaking
the bottom curve in the initial sweep.
Anyways out of time fellows!

Cheers and thanks for listening!
Attachment:
Sweep_1-railh.jpg
Author:  Bob Hames [ Thu Jul 07, 2011 6:21 am ]
Post subject:  Re: Rhino help with Volute area please
FYI
Well I believe this approach will work after a little fiddling around.
I made few goofs and it's very rough, but it's basically what I was after.
If you think about it it is pretty well Trevor's method from his tute.
I'll post some pics of my first neck off the CNC when I get it machined.
All comments,questions welcomed!

Bob
Attachment:
Sweep_1-railhi.jpg
Author:  Parser [ Thu Jul 07, 2011 11:31 am ]
Post subject:  Re: Rhino help with Volute area please
Looks good! The transitions all look pretty smooth to me.

Trev
Author:  Marty M. [ Thu Jul 07, 2011 2:30 pm ]
Post subject:  Re: Rhino help with Volute area please
I'm not sure that I can be of help as I'm in the learning curve as well, but I'll offer some observations from my own struggles with Rhino. I've found that sometimes the surfacing tools work better on more simple curves. What I mean is that I'll take a complex curve and break it into a couple simpler curves. Sometimes this means creating extra straight lines where surfaces would be attached together later. I have had a lot more luck in mirroring surfaces on a centerline than trying to get one surface across the whole area. Also, creating edges from surfaces after you delete them allows you to easily get back to curves that may be useful for the surface creation because sometimes a surface edge wont be enough to do what you want. Lastly, extruding a surface into a solid and then splitting part of it away to leave what you want, seems to be something that rhino likes to do over boolean differences. In my jpeg you can see the various surfaces I used to get the tele style neck. I'm not saying that this is the best way to do this...but it worked.
Author:  Bob Garrish [ Mon Jul 11, 2011 4:02 pm ]
Post subject:  Re: Rhino help with Volute area please
It's a big topic, and I don't have much time to write on it, but there are a couple tidbits I think are worth mentioning:

+1 on mirroring and using simple curves

Use rebuild to get the involved curves down to as few control points as possible (ie: maximally smooth) and also try to match the number of control points on opposed curves. That makes the surface more uniform and prevents 'kinks'.

Oftentimes a trimmed surface is your best bet vs building the surface to final dimensions. That was how I did nearly all my complex surfacing until many hours in.
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