Official Luthiers Forum!

Well, I have had Rhino for nearly a year now and my skills are improving but the 'perfect' curved instrument surface is still elusive. I'm getting closer, I think, but the devil is in the details. I have always been one who likes to learn by doing and am usually successful at figuring things out but I have to say that drawing and surfacing these 3 dimensional curves has been one of the steepest learning curves I have experienced. So it's time to ask for some help.

Here's are some captures of the A5 that I have been working on The underlying curves, the wire frame version and the render. In the rendered version, the recurve seems to have disappeared. Is the lack of recurve in the render just a limitation in Rhino? the recurve is definitely there in the station curves. I haven't cut this yet (still waiting for my CNC) so I'm not sure what would happen there. Come to think of it I have seen gentle recurves in other people's renderings.

I would love to hear how others would approach a project such as this. My process has been to:

Scan in the plans (tricky but doable on a small scanner - I'll have to try a copy center next time)
Clean up the scans in as much as possible in Photoshop
Convert the bitmaps to vectors either by setting them as backgrounds in Rhino and then tracing over them or by using the 'Fit Vectors to Bitmap' feature in VCarve Pro
Mess around with the vector curves for what seems like forever in Rhino until everything lines up. Trimming, rotating, extending, splitting, joining or whatever is necessary
Creating a surface using NetworkSrf

All of which takes a very long time.

Thanks

Scott

Scott it is funny that I am here offering you help and need help myself on a carve top. I have done a Les Paul that looks decent, but this current design, I cannot seem to get it to work. I am sure it is my messy curves.

Now with that said, if you will add a few more curves on the "vacant" end of the top, use patch command, you will likely find good results. Since your instrument is symetrical this should fair out nicely. Another little tidbit for you. It looks as if you are drawing both inside and outside surfaces. Unless there is a difference between the two, create the top surface then offset it for your inside surface.

Mike

ps...the top I am attempting is not symetrical, and is a single cut....I need help as well!!!

Ask and ye shall receive

I'm not a mandolin builder - and the surface may not be truly accurate - but I did this quick video tutorial to show some basic surfacing techniques that have served me well. Be forewarned, this is sped up 4X to shrink the video to acceptable size. Also - sorry about the "stretched" video...not sure how that happened.

Trev

_________________
http://www.PeakeGuitars.com

Thanks for the replies.

So far I have just used the curves that were on the plan (three cross sections) but it may be that I need to add some more. I'd hadn't thought of offsetting to get the inside surface. They aren't exactly the same but probably close enough.

Trevor, I really appreciate that you took the time to make a video. Even watching it full screen on YouTube at 4X speed it was kinda hard to follow. I am particularly interested in what you are doing at about 1:20 where you start surfacing. Perhaps you could post that 30 seconds or so slowed down?

Thanks

Hey Scott, here is a realtime version of the actual surface commands. The basic surfacing steps are as follows:
a) use network surface to form the upper half of the body surface.
b) use the center profile to split that body surface in half, right in the middle
c) do a straight extrude on the central profile curve in the back half of the body. This is for construction purposes only. We will use this to form the lower left quadrant of the body.
d) Using the blend surface command - with the tangency option set - first select the back edge of the upper body surface and then hit return. Then, for the 2nd edge, select the inner edge of the straight extrude. This blend surface command will then fill in that quadrant with a perfectly formed sweep that is tangent to both surfaces used to construct it.
e) Delete the straight extrude construction surface
f) mirror the lower left quadrant to make the lower right quadrant
g) use the Analyze > Edge Tools >> Join 2 Naked Edges command to clean up the seams and to join those surface sections.

It looks like you have a good framework setup. I'd recommend forming those lower surfaces as I demonstrate it in the video - if you use a network surface to form these surfaces you will never quite get them right. Sometimes you'll get a "pinch point" at the very back center point where the surface terminates. The technique I show in this video will make it perfect, every time.

Also, another point to keep in mind is that surfaces generally work best when they are 4 sided. Looks like you are almost there.....! Nice work!

Trev

_________________
http://www.PeakeGuitars.com

Trev,

What was the function you did when you extruded the end "half" of the to the side? What was the purpose of that?

Is this method as easy to do with an asymetrical body, single cut and carved top similar to a PRS, though the body looks nothing like a PRS? I that made sense to you didn't it??

Mike

Trev's already given some great advice on modelling the surface, so I'll just add a +1 there. A screen grabber that allow captions or grabs audio would make the videos easier to follow for those who aren't already very familiar with Rhino. I sound horrible on my computer's mic, but I suffer for the cause

So far as what's happening on screen, it looks to me as if there's an accidental planar surface through the top contour curve. The very top section of the mandolin top (not covered by the network surface) still has a surface there and it only covers up the parts of the carve below parallel, so it's a dead giveaway. I suspect it happened when the outside contour was extruded and Rhino capped it?

Anyhow, to get rid of it: select all surfaces with selsrf then selpolysrf, explode them so they can be selected individually, then click on and select that top surface and delete it.

Mike:
The surface he creates with blendsrf is tangent to the surfaces at either end of it. The extruded surface he creates using the center line (just with extrudecrv) is created to be the second tangent reference for the blendsrf

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Therefore my question! If the surface is extruded to the side, why not create the network surfaces using that curve? Would the two halves not be tangent?

There is soooo much I don't know about Rhino!

Mike

The two halves would be tangent, but if you look at the ISOcurves that form when you do that, you'll notice that it is "pinched" at the very back in the middle. You actually don't have very good control of the surface in this area if you do it this way because of this pinching effect. Rhino is basically trying to build a 2 sided surface out of a profile that is continuous, hence the pinch (it's a corner in which the two lines are tangent, if that makes any sense).

Building the surface as I show it gives you complete control over the surface and will keep everything tangent in that area. It's a technique that took me awhile to figure out, but once I did it made this type of feature much easier to make. I've tried plenty of times to build surfaces as you are doing, but it just never works out.

A PRS style body would use similar functions, but you have to break the carve into a number of different areas because of the way the upper and lower bouts are carved, as well as the hand carve. The PRS carve is pretty tricky to do well.

Good luck!

Trev

_________________
http://www.PeakeGuitars.com

Progress is being made. There are still a few anomalies to work out (the black dot in the center where all of the surfaces join and a few other small surfacing issues) but I am definitely on the right track - it actually looks like a mandolin top! I also did some work on the neck and I thought it came out pretty well. I used Trevor's guitar neck tutorial as a starting point. On to drawing the back next.

I'm sure I will have more questions as I ponder the why and how of what was done. Then there is F5 the curvier brother of the A5 and that very curvy rocking chair seat I want to machine. And how would I add a diamond volute to my guitar neck? So many questions, so little time.

For now, a big thank you to everyone who replied and especially to Trevor for his video.

Awesome, I'm glad it helped you out! I've learned a lot from browsing this forum & am happy to chip in with the few things I can offer.

Best,
Trev

_________________
http://www.PeakeGuitars.com

You guys need to offer an on-line class RHINO FOR DUMMIES for guys like me.
I've been using ProE 3D (day job) for about 10 years now but won't be long before I'm retired and will need to buy Rhino.
Nelson P.S. With that said, all the posts here are very informative and useful. It takes time to post all the videos and screenshots let along the explanations.