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You guys have been great at helping out when people have questions. I have one that I hope somebody can answer. When I draw a neck, I have a fairly long surface for the neck shaft,and that connects to transitions at the peghead and at the heel. When I cut this out I notice a distinct mark in the wood at those points. I've joined everything together. My question is....Is there a command that smooths out the joint so that this mark won't show up? Thanks in advance.

I don't know Rhino but what you need to do is maintain tangency to the neck profile when you sweep your curve in the transition. That's probably a checkbox or something like that in the sweep or loft dialogue when you created the transition.

Knowing that Rhino doesn't have a design tree, it may be hard to go in after the fact to fix it though (don't know for sure though). So, the quick fix would be to select the two surfaces and put a fillet with a large radius, like 1" maybe but experiment, between the two surfaces. The fillet will have the effect of maintaining tangency between the neck profile and the transition profile.

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http://www.birkonium.com CNC Products for Luthiers
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When I create the transition surfaces, I use the surface edge of the "shaft" as the corresponding curve in the surface network. I would think this would make the next surface tangent. The surfaces do join together into one surface. I don't know if it just the router stalling in that spot for a millisecond or play in the router bearings, or even minimal bending of the shafts.... I was just wondering if others had the same experience.

Hmmm.. As I said, I'm not an expert in Rhino but, when you're using the edge are you talking about the "D" shaped profile or are you actually selecting the surface itself?

It's possible that if you're selecting the profile, the transition curve starts out normal to the "drawing plane" of the profile which isn't necessarily tangent to the neck surface. Does that make sense?

Zoom in really tight on the transition and see if you can see a ridge.

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http://banduramaker.blogspot.com

I don't know what to say about that because you have a choice of using a curve if it is there or the edge of the surface. I usually delete any curves when I'm creating the surfaces. Hopefully a more advanced Rhino user may chime in. Thanks for the ideas though....

I've had the exact same experience using Rhino, though I really don't think it's Rhino-specific. I don't have a good answer for you--I think Andy's suggestion about the large radius filet makes sense though. I've gotten around it just by fiddling around with those transition areas, doing additional lofts or sweeps to bridge the areas in question. Pretty un-scientific, but it's gotten me past any real problems. When I cut a neck now, there is still a hint of a line at these transition points, but nothing that doesn't easily sand out as I refine the neck. My goal has always been to use the CNC to replace a shaper in roughing out a neck. What I've actually gotten is much more refined than that, but it's still not a "sand it with 220 and lacquer" kind of deal. I take my necks off the CNC and start sanding at about 150 to take out the remaining tool marks.

One thing I've noticed though is that when sweeping along curves to do the heel/peghead transition, setting the tolerances tight to the curves I'm sweeping reduce the problems at the transitions. The default on a sweep is a pretty loose following of the curves.

I'm still a novice at this, but I'm stubborn and have been finding ways around my problems that might or might not be the easiest or best ways, but ways that work....

Dave

Same problem with cutting metal on mills. Sometimes a programmer does some little sleight of hand to keep the cut smooth. So guitar builders aren't the only ones in that boat....

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"Act your age, not your shoe size" - Prince

Does this happen at all feed speeds?
Perhaps a slower feed will keep the tool pressure down so there is no bounce when changing direction.

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How long is that in luthyears?

You have to make real light cuts when you get down to the final passes.

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"Act your age, not your shoe size" - Prince

Marty, this might also be within your tool path, depending on how you created them. What cam system are you using? If it is Madcam, I can probably help.

Mike

The join command doesn't necessarily make a surface, it might just be making a polysurface which is just a group of surfaces. A real surface will only give you gaps and blips if they're mechanical or if the curvature forces your tool to move off of the surface.

There are a lot of things that can cause witness marks, so I'll wait to see your answers to the other questions posed here before I make a guess at the cause. As someone else mentioned, there are different measures of continuity at surfaces (position, tangent, curvature) and to get the higher order (smoother) transitions like tangency and curvature you need to build them in on purpose.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks for the responses. Well,I hope speed isn't too much of a factor as I'm going about 50-60. I'm taking a stepover of about .060 on the final cut and maybe .050 deep although I'd have to check my files to be sure. I'm using a .5 dia Freud roundnose router bit in a PC 690 on the K2. I'm sure that a rigid machine, new router, and bit might provide a better result, but this is what I have available. The necks come out nice and the marks can be sanded out. Obviously not being a machinist or Rhino student has its drawbacks. I just thought maybe there was something obvious that I was doing wrong that was easily correctable. Is there any way to make a neck seamless instead of combining surfaces? I'm using meshcam too.