Mirror, mirror on the . . . um . . . screen

[Anonymous]

Been mirroring sketches for some time with no trouble. Handy because I usually work on one half of a symmetrical drawing to get the bugs out, and then I mirror it.

Yesterday I mirrored half a surface of a musical instrument arching. It appeared to go well, and when I was done all I had to do was stitch the two halves together in preparation for thickening it. Then things got odd. After the mirror, the two halves were displayed in F360's default steel color. After the stitching, the original half stayed steel colored, while the mirrored half took on a nice brassy color.

When I thickened the surface, one half thickened in the plus Z direction, and the other in the minus Z direction. This seems to make any further operations, such as trimming, impossible. Is this a bug? Anyone know how to squash it?

[laughingcreek]

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@Anonymous wrote:

...Also, I did not see the attachment you posted....

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Just checking that you do see the attachment now? its at the bottom of post 10, a file named violin.f3d.  you can open it and look.

A few thoughts from the prospective of someone who has made the models and tool-paths for an arch-top guitar maker for a while now.

-I have done models using both nurbs lofting, and tsplines.  it seems like the t-splines would be to in-accurate, because your eyeballing a lot.  Having seen the results of both I prefer t-splines.  Especially if I don't nail the surface the first time and have to go back and make adjustments.

-with both lofting and t-splines, less is more.  fewer control points on splines, fewer overall profiles, fewer t-spline faces will all contribute to smoother surfacing.

-t-splines is nothing like brep/nurbs modeling.  It's a different skill set.  a lot of the youtube tutorials frankly suck.  Sub-D modeling is very close analogy to t-spline modeling.  There are some difference, but it's close enough that it is a good place to start learning.  There is a LOT of info and tutorials on sub-D modeling.  It's the "topology" you want to figure out.  You want to figure out how to use all quads, and where to place star points and loops.

-we found that even when using sharp bits, and being very careful with the tool paths so that the bit is always cutting while climbing, there is still a certain amount of sanding required b/c the bit seems to "bruise" the surface in places. and there always seems to be at least micro tearing.  the surface will look good right off the table, but if you just lightly sand and finish you can see all sorts of problems.

-A lot of correction can take place while sanding, but lumps and valley shaped creases are HARD to correct 

-we re-curved the tops in the model in the beginning, so the entire surface was cut in one go.  I still prefer that.  The guy actually building the guitar prefers to have control over the re-curve.  he does it while sanding.  Potato patato. 

[TrippyLighting]

I aim still experimenting, however, this little screencast showing the current work in progress should indicate that this can be done in Fusion 360. Considering how I created this surface ( a  loft with 2 profiles and 5 rails) I am surprised that it creates this smooth of a surface!

Now that we have the main surfaces, we "simply" have to blend between them.

[eliomiller]

Just another idea I used myself to create that type of backplate,

create an extrusion of the violin outline you created in 2D (try to keep the semi-circle part out of the loop for later)

then use the split body tool to achieve the shape you want. another thing you could also do would be to duplicate this t spline surface and offset it and use both to cut the body, and you will have your finished plate! I attached a work in progress I was working on myself recently. Kind of funny we are working on the same thing around the same time.

[TrippyLighting]

Here is a link to is one of the best T-Spline tutorials I've seen so far. This is Gichi Endo's channel and he models a car.

In the Sub-D modeling what he's doing is "hard surface" modeling and that is what this top and bottom surface require.

[Anonymous]

Hi, CADWhisperer--

I have tried a few times to open this file, and I always get an error message about some kind of like being missing. Not sure why it isn't loading. I might have written to you about this already, but in case the old brain gears have slipped a cog, I just wanted you to know that I wasn't ignoring your help!

--Bob

[Anonymous]

Hi, wmhazzard--

The way to draw this specific violin (The Stradivari Model G, considered his finest design) is derived from the ancient method of using the golden section and drawing with dividers, a compass, and a straightedge. It is amazing to see the precision coming to us from the early 16th century, especially since golden section geometry deals entirely with irrational numbers. Approximately around 1735, the process followed by the old geometers was lost until a small group of perhaps half a dozen of us independently began to rediscover it about fifteen or twenty years ago.

In 2008, I wrote a series of articles on drawing a violin using the golden section for American Lutherie magazine, no. 93 (body), no. 94 (ff-holes), and no. 95 (scroll and pegbox). These back issues might still be available at www.luth.org.

I used an excellent 2D program called DesignCAD because it gave me iron control over my large-format plotter. I still wish I could send my Fusion sketches to a plotter as many people prefer this kind of output. Since then, and since trying to expand the process into 3d with Fusion, I have realized that I needed an even finer resolution than before, and I also made all the usual stumbles when coming up the very steep learning curve of an amazing piece of software.

Just one example: the tangent functions of Fusion will sometimes create what I desire, but it took me a while to understand that in order to do so Fusion will move the centerpoint of the arc from its reference mark on my grid. Since this point can also serve as a reference for other circles or arcs, and I didn't notice at first, some interesting confusion (not to mention some interesting language) was often heard in my house.

The results in Fusion are even better than before, and it is still amazing that the old way remains very precise and accurate.

[TheCADWhisperer]

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@Anonymous wrote:

Hi, CADWhisperer--

I have tried a few times to open this file...

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What file? I do not know what file you are referring to?

[Anonymous]

Greetings, laughingcreek--

I own an early copy of Rhino, which uses non-uniform random b-splines, but to get the CAM functionality the costs were prohibitive for me at the the time.  So Fusion 360, here I am! I've done a couple of arched tops using splines (will post my latest in a few minutes when I answer TrippyLighting's post), and it is a chore as the work goes on to have to adjust, re-adjust, and then adjust the spline points again. It looks as if it might be possible for my specific needs to get lofts to work, which would be nice if it is possible to edit them.

Still very new at this, and I am hoping to understand quads, star points, and loops since I think they would apply to the recurve of the arch. Can you point me to some good tutorials?

The surface of wood after routing always creates problems. It's why small irregularities didn't bother me so much since I'd planned to  deal with them while surfacing the wood with steel scrapers (never sandpaper!). I know a gentleman who explained that by altering the bevel on round-nose bits a lot of the tearing is diminished. I'll have to write to him and see where he got the bits or if he had them specially made.

--Bob

[Anonymous]

Peter--

This is amazing. I fooled a bit with lofts, and except for controlling the area it covers I thought it went really well. Can you explain how you selected the profiles and which rails you used? If I could go back to using the original set, it would greatly simplify the process and result in a much tighter sketch.

The drawing as you left it is exactly what I had envisioned. The flat shelf around the perimeter gives a secure mounting surface when the work piece is flipped over to rout out the interior arching. When done, there will be a flat shelf on both sides, the work can be flipped back to its original orientation, and then the purfling groove and recurve and be cut. If you're thinking that the part should be fully modeled, have a go!

I've included my latest arching effort using my guide arches and spline planes. Thanks to all of you, I got the "flipped" mirror error to go away, and I eliminated all the irregularities in the arching . . . I think. Let me know if this effort represents and improvement over my earlier efforts. And if you want to loft v20, I'd love to see the results.

--Bob

[Anonymous]

Great minds run in the same ditch, as they say. See my earlier post to wmhazzard to find out more about the method of creating a plate with geometric design. I'm a near-total Fusion wimp for the time being, but I do know a lot about violin geometry. Congratulation on your effort

[davebYYPCU]

Not trying to divert your train of thought, but picking up on your comment in message 26 above, Fusion can deliver large format plotter output, too.

Depending on your requirements, and software / hardware, Fusion exports single sketches as dxf.  With an Addin called DXFer (from Github) you can export multiple faces to a single file.  

I am admiring your enthusiastic tone.

[Anonymous]

Thanks, DavebYYPCU--

I appreciate your advice about plotter printing Fusion sketches and
since my old CAD program accepts .DXF files I might be able to get it to
work that way. Otherwise, a white-knuckle enthusiasm is sometimes all I
can bring to a challenge. Probably better than nothing!

[Anonymous]

My college orchestra director used to say that if you beat your head against a brick wall long enough, sooner or later one must assume the shape of the other. But I've been sledging away and have learned (almost) how to create a really excellent surface on my model following your idea to do it with lofts and profiles. I started out with around 30 construction planes the way I was doing it before, and most recently got that down to about 12 rails and about the same number of profiles. I think it can be done with even less once I get more experience. I got so engrossed in figuring out why Fusion 360 hates splines used in loft profiles that I fried my brain cell (singular) and afterward couldn't for the life of me figure out how you got that flat platform around your version and then thickened it (4 mm would have been plenty, by the way). I tried extruding it, but that always crashed Fusion so I stopped. I'm hoping you can tell me a fairly easy way to do it as this will put me over the last huge obstacle in my way (until the next one). Thanks again for your insights, and I will take a break here and pick mortar from between my teeth while waiting for your reply.

[TrippyLighting]

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