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heel to neck transition - SW
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10106&t=39357		 Page 1 of 1
Author:  Glenn C Foster [ Fri Feb 15, 2013 6:07 am ]
Post subject:  heel to neck transition - SW
Hi Guys and Gals - Hoping for some advice on modeling a neck in SW, i seem to keep getting the same issue no matter what i do.. gaah especially when it should be such an easy thing to do!

I seem to be having problems with the heel section and the transition from heel to the neck contours deviating. instead of being a smooth transition it seems to dive down slight below the neck contours and then back up (as per pic highlight with red).

My Process for drawing the heel transition is create a series of boundary surfaces, then for the actual transition use a surface fill, ensuring that the neck selection edge is set to tangent.

Is there something stupid that I'm not seeing? or am i just going about the whole thing the wrong way? [headinwall]

Many thanks
Glenn
SW file also below:

http://speedy.sh/hNxt6/Test-Heel1.SLDPRT
Author:  Andy Birko [ Fri Feb 15, 2013 11:52 am ]
Post subject:  Re: heel to neck transition - SW
First of all, remember that I'm trying to help you so please excuse my venting - your model is an absolute mess!!! [headinwall] Always put planes at the top of your design tree before you make a single sketch. The only sketch that's allowed to go before any created planes is a master model sketch and some would say that even that's too much. Had you done that, this would have been done an hour ago. /vent

You've got a number of things you're doing that I'd do diffeerently.

1) I'd only do half the neck and mirror it.
2) NURBS is bad at modeling 5 sided surfaces so the trick is to make the blend with two 4 sided surfaces, one of which is trimmed to a 3 sided surface.

3) Here's what I did. I had to abandon your heel because the model was too screwed up to fix it without starting over from scratch. The comments will describe each step

I run Solidworks in a virtual environment so some of my edges don't look as good as they could. Good luck.
Author:  Andy Birko [ Fri Feb 15, 2013 12:06 pm ]
Post subject:  Re: heel to neck transition - SW
p.s. the zebra stripes don't look good on the transition from the trimmed surface to the heel but in real life they work out fine.
Author:  Stuart Gort [ Fri Feb 15, 2013 12:11 pm ]
Post subject:  Re: heel to neck transition - SW
Read the caption of each pic which identifies the SW elements depicted.

This will perhaps offer a way of looking at the problem that you haven't yet considered.

This neck and heel are a single surface lofted not from end to end but from long edge to long edge. There are only three lofting sections. Two of them are 3D sketches. Technically there are only two lofting sections since the 3D sections are simply mirrored.

Angled planes must be constructed so the various guide curves can be placed. But once in position, each guide curve offers the ability to tweak the shape until you get what you want.

It's maybe not the easiest way to go but I think it offers, by far, the most versatile way to tweak the shape.
Author:  Andy Birko [ Fri Feb 15, 2013 12:43 pm ]
Post subject:  Re: heel to neck transition - SW
Stuart,

I really like that concept except that you still have a degenerate point on your surface. If you combined the method I showed to eliminate the degenerate point with your method you could eliminate some of the ridges (at least they look like ridges - I can't zoom the images) while giving up almost none of the flexibility of your method.

Four sides will always look better in NURBS than 3 or 5 sided parts.
Author:  Stuart Gort [ Fri Feb 15, 2013 4:43 pm ]
Post subject:  Re: heel to neck transition - SW
What do you mean by "degenerate point", Andy?

I think you might be referring to a wrinkle right at the base of the neck shank (?)...but this was just a demonstration slapped together for someone....not a model I spent any time with. A small tweaking of a nearby guide curve deals with that.

And besides....220 sandpaper generally takes out anything I leave in a surface model....in a few swipes. That's one of those things I also used to strive over that I came to undserstand was a waste of time. :)
Author:  Andy Birko [ Fri Feb 15, 2013 5:04 pm ]
Post subject:  Re: heel to neck transition - SW
I'm not an expert at the math behind nurbs but from what I understand, it works best on surfaces with 4 corners or edges. So, for the model that you have, there are actually 3 sides that you're lofting with the one "corner" being the degenerate point. There are other instances for degenerate points as well. Sometimes they can work out well and other times, they can cause that wrinkle.

I'll admit that I never tried your approach on a neck to heel blend but I have done the "opposite" loft than I thought of at first (i.e., switching the guide curves for loft profiles) but I have in other instances and it helped get rid of a ripple tremendously.

If you were to take the first part of my method (which I actually learned on cad junkie) and trimmed it just like I showed and then used that edge with no corner in it, I think you'll get a perfectly smooth loft.

I like these discussions because it's always nice to have a lot of arrows in the quiver.

I'm a fan of getting the surfaces nice to begin with and the more I'm experimenting, the more I'm learning that it can be done quickly if you learn a process and follow its guidlines when building. What that does mean is that there's a bit of sitting and pondering about how you're going to do something before you start adding features and sketches to the design tree!
Author:  Bobc [ Fri Feb 15, 2013 5:44 pm ]
Post subject:  Re: heel to neck transition - SW
Zlurgh wrote:
And besides....220 sandpaper generally takes out anything I leave in a surface model....in a few swipes. That's one of those things I also used to strive over that I came to understand was a waste of time. :)


+1
Author:  turmite [ Fri Feb 15, 2013 5:51 pm ]
Post subject:  Re: heel to neck transition - SW
+2

Different industry, but still wood...I discovered, regardless how much extra time I spend machining, I still have to sand, and all that extra time machining could have been used for sanding anyway.....now that is the way I do it. Close and sand!

Mike
Author:  Andy Birko [ Fri Feb 15, 2013 6:34 pm ]
Post subject:  Re: heel to neck transition - SW
The thing is that there's no extra time involved here in neither machining nor design...but less time sanding :D I assure you that Stuart's method is just as or more labor intensive than mine but, mine gives a surface that's smooth to begin with.

This is just a matter of getting the surface right to begin with by keeping a few points in mind during design. Obviously you're more than welcome to choose whichever method you desire.

In my first neck model I struggled for hours to patch a 3 sided 3D surface and got ripples at the edges that I in fact did sand out. Now that I know how to do it, I can get a result that needs hardly any sanding in a 1/4 the time.
Author:  turmite [ Fri Feb 15, 2013 9:58 pm ]
Post subject:  Re: heel to neck transition - SW
Andy I wasn't necessarily commenting on the smoothness of the model when I made my statement. I carve full 3d in a wide variety of woods and in my experience, the added machining time between a .060" step and a .030" step is just not justified because I still have to sand the part. For me, it is a simple matter of time management, because my sanding equipment can smooth the difference much faster than my cnc can carve it.

Mike
Author:  Glenn C Foster [ Sat Feb 16, 2013 4:35 am ]
Post subject:  Re: heel to neck transition - SW
Hi Guys - Thanks for all the responses.

Quote:
First of all, remember that I'm trying to help you so please excuse my venting - your model is an absolute mess!!! [headinwall]

Ahaha sorry Andy, I know I need to clean things up a bit, i think i also need to do all of the SWtutorials to make sure I'm doing things the right way, most of it I've just tried to figure out myself :) I'm lacking the basic grounding with SW.
I'll work your steps and see what I can come up with.
One question though regarding the first step, are you creating a plane for the sketch (14)? or are you just drawing 1 reference line on the same plane the heel 'cap' is one?

Stuart - thanks, i will give your method a shot as well, what i like about yours is being able to adjust the heel by modifying the guide curves.

Couple hours free now so I'm going to get busy, thanks again guys really appreciate the guidance
Cheers
Glenn
Author:  Andy Birko [ Sat Feb 16, 2013 9:16 am ]
Post subject:  Re: heel to neck transition - SW
Hi Glenn,

Yes, I just used the heel cap plane to draw a line for that initial loft.

I think Stuart's method is a very good idea too. Since you're just experimenting, it's worth trying it without any guide curves and just use tangency controls to see how that works out as well. Although skipping the guide curves gives you less control over the final shape, it can result in a smoother final surface. The rub is that if you don't use guide curves you can run into unforeseen issues if you make changes higher in the design tree.

You should also try a combo of my method and Stuart's - I'm kind of thinking that might be the bomb. Basically start with a 4 sided loft for the heel with a line at the fretboard plane (front), the heel and a guide curve to give the heel shape you like. Trim it with a spline like I had in step 2 of my post and then do the loft like Stuart does.
Author:  Stuart Gort [ Sat Feb 16, 2013 1:12 pm ]
Post subject:  Re: heel to neck transition - SW
I'd also add, Lappy that depending on your version of SW, the "Freeform" tool would have dealt with the issue in your original post QUITE easily. It would allow you to completely eliminate the vector issue you highlighted.

Actually...the freefrom tool is a small miracle for dealing with issues EXACTLY like yours. It allows you to choose a bias on a surface, make a guide curve or curves (essentially like a 3D intersection curve) along that bias, create points on that curve, and then pull each point of that curve any way you like to alter the surface. Basically, it can save hours of tweaking with organic shapes like the heel or volute area.

If there was any reason at all that you were considering upgrading your version of SW....the freeform tool will blow your reason out of the water.

Or maybe you have a later version with freeform? That would be nice. I have 2012 but I don't know when they introduced the tool.
Author:  Bob Garrish [ Sun Feb 17, 2013 4:35 pm ]
Post subject:  Re: heel to neck transition - SW
Andy Birko wrote:
I'm not an expert at the math behind nurbs but from what I understand, it works best on surfaces with 4 corners or edges.


Always, and it is totally a result of the math. OTOH, that math makes quads work oh so well.

Without question, all the worst CAD problems I've had to deal with happened because I was trying to solve a problem with non-4-sided surfaces instead of figuring out how to solve it with them. Now, unless it's an unimportant or flat patch, I just start on figuring out how to turn it into something that can be made with quads right away. The one place three sided surfaces work is when they're sections of a surface of rotation or an analogue like a two-rail sweep with a degenerate rail, but that's a special case.
Author:  Andy Birko [ Sun Feb 17, 2013 4:57 pm ]
Post subject:  Re: heel to neck transition - SW
Bob Garrish wrote:
Now, unless it's an unimportant or flat patch, I just start on figuring out how to turn it into something that can be made with quads right away.


Pretty much the exact point I was trying to make!
Author:  Glenn C Foster [ Thu Feb 21, 2013 8:50 am ]
Post subject:  Re: heel to neck transition - SW
Just wanted to say a quick thank you for everyone's guidance and help on this.

I managed to finish the neck and feel as though I have gotten a much better finished product, also i have learnt heaps about SW and surfacing.
I've attached a couple of pics of the finished product. I actually ended up being able to model the neck that was in my head as opposed to the neck that i could only draw with the lack of skills i had.

Biggest takeaways I have learnt are that when surfacing stick to four sided surface selections, makes a huge difference in the finish. Secondly the use of the tangency to face feature in boundary surface, this along with the guide curves really helped to get the perfect transition.

Any way thanks again guys really appreciate it... time to go and cut this thing out now!

Cheers
Glenn
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