Thanks Jim. I’ll have to take a look at the outer curve points.
Basically, I am trying to create a form that will serve as the bread on my ‘sandwich’ to press thin veneers I to shape.
Radius dishes are commonly found at guitar tooling shops but custom dishes, not so much unless one hand-carves them or uses a CNC - the latter of which is what I’m wanting to accomplish.
Thanks Stratosfear.
At risk of sounding daft, could I trouble you to post a video showing what you mean by rebuilding the curves and building the surfaces from the edges with editable Bézier curves?
This is likely basic stuff but I’m fairly green at this point in time.
Hi @mbhwhitney
You are getting lots of help now. This time I’ll keep my comments focused on making the centerline arch.
Your posted file reveals the first problem which is that somehow I think you messed up when you measured the guitar. So if you don’t want to just buy a set of plans you will need to get a sample guitar again and measure more carefully. @JimD did a great job of explaining how to get sufficient information from a physical model without high tech probes or laser scan.
You do want your curve to pass smoothly through your target points as closely as possible in the beginning. If your ultimate goal does not require a precise duplication of a sample and you are experienced you can draw with less strict adherence to measured data. However I suggest that you err on the side of more measurements -say every 1"- then later you can smooth out the curves keeping your original for comparison.
Once you have a centerline drawn you can use Rebuild as suggested by @davidcockey I also like to use Fair and SoftEditCrv. Keeping the Curvature Graph on while you are working will help you understand the result.
Re my comments about using SetPt to create co planar perimeter please keep the end blocks as well as the sides and lining in mind from the beginning. Make sure your curves are flat where they need to be before using them to create a surface. There is a great explanation of how to use this command in the online help.
Thanks Abraham -
Unfortunately, getting a hold of the guitar again is not possible and there are no plans available for this model (I’ve looked high and low). As such, I’ll have to rely on my sketches and take artistic license, deviating slightly from the original, which I’m fine with.
I appreciate all the comments and support.
Hi @mbhwhitney - let’s start with your edges. See attached image showing 3 options. If you are committed to a laminated construction and a flat co-planar intersection with the sides-linings-blocks, this will influence the angle and curvature a lot as it leaves the edge. Please post your best solution for your center profile all the way down the middle of the back and I will try to help you through the rest of the way.
Thanks @abrahamwechter.
I tried the method @jeremy5 suggested and found that Rhino5 on Mac does support CurveThruPt - at least as far as I can tell.
As such, I modified my centre curve and set the degree to ‘5’ - not sure if this is what @Stratosfear meant. From there, I set ‘curve type’ to ‘control points’ (if I remember correctly).
With this approach, it smoothed out my curve significantly and I only had to make slight adjustments to my vertical reference lines.
I then tried the same method to the top-most curve, intersecting the centre-line. Choosing ‘interpolated’ from the parameters, ‘knots’ set to ‘chord’ and ‘degree’ set to ‘5’ resulted a curve that intersected the centre-line and constrained to that point.
I followed the same method for the next lateral curve but even when playing with the parameters, the result is not very fluid / not desirable.
‘Knots’ set to ‘Sqrt Chrord’ looks the best but still not quite right.
That’s as far as I’ve gotten today. I’ve attached the most recent file.Back_Recurve.3dm (2.7 MB)
Hi, I am going to suggest something that might be way off, so here goes.from your last image it looks like you are trying to make a curve through those highlighted points. First, should the reference lines to the right and left he slightly lower than the center point? If so, I would try Circle from 3 points. Touching the ends of the curves one step away from the center curve. Next , to the center curve. Split this circle at the beginning points where the circle was made. Then, rebuild the kept part to a degree 5 curve.next, draw a line horizontal away from the guitar body a little distance. Next use Adjustable Blend curve to connect the two curves.
Hope it helps. —-Mark
I would watch a video on vimeo about making a spoon in rhino… it had some very interesting modelling tricks on keeping the points to minimum and at the same time manipulating curves in a controlled way.
Hope its useful
Clem
Hi @mbhwhitney
Just a few minutes now to look at this…
I see you have made substantial progress by disregarding some of your original height measurements and going for a smoother result. This is the right direction in this case.
Before you go too far I suggest that we go back to my question about the edges. As you have drawn there will be gaps between the inside of the back and both the headblock and tailblock, and also the cutaway area will need to be pressed down. If you clamp these areas down when you glue the back the distortions will show.
The first step really needs for you to decide if you can use a hollowed sanding dish to prepare the side assembly or if it will be flat (co planar). If you can use a hollowed dish your angle as it leaves the edge can be higher and perhaps more attractive. Either way the ends of your curves need to match the glue surface of the side assembly for the full extent of the intersection. Once we have the ends in place we can work the curvature as it curls up to a dome in the center.
_CurveThruPt supports history: start the command and - before selecting any points - turn on Record History - then select your points and create your line. If you don’t like the curve you can select points and move them up and down with the gumball. The curve will follow them. For relatively shallow curves like these you may find this easier than editing the control points. By picking the matching pairs of points each side of your centreline together you can preserve symmetry (provided you started with it 
).
Note that Record History turns itself off when the command it is within completes so you need to turn it on each time you draw a line. See the help file for more details.
Regards
Jeremy
I assume everyone means CurveThroughPt when they type CurveThruPt.
My testing in V6 shows that CurveThroughPt and InterpCrv result in exactly the same curve with the same set of input points if the CurveType=Interp is selected in CurveThroughPt and the Degree and Knot options are the same. Differences in result are probably due to differences in option selection.
InterpCrv allows direct input of point locations without a point object being located at the location but requires sequential selection of the locations and is not History enabled…CurveThroughPt requires point objects as input and allows selecting all the input points simultaneously and is History enabled.
Added: CurveThroughPt with CurveType=ControlPoint results in inherently smoother curves than with CurveType=Interp but the curve will generally not go through every input point.
Thanks Mark - I’ll make a duplicate of the model and try that out. The centre point is, in fact, taller than the other points.
Cheers - Mike
Thanks Clem - I’ll look that video up!
Mike
Hey Jim - any idea why the inner curve would have the stacked points? I deleted it and then simply made an offset .5” inward and it gave the same result.
Thanks in advance.
M.
Hi Abraham,
Thanks for the encouragement and support thus far.
Regarding your question, the side details I’ve drawn reveal a very flat profile where the back meets the sides (not so much for where the top meets the sides). To this point, I will devise some form of dish to work the sides, kerfed lining and end blocks to meet the ‘flats’ (‘zero’ points) of the recurve. I think we’re on the same page here.
I sent you a PM as well.
Cheers -
Mike
Hi @mbhwhitney
I am posting a couple screen shots and a file that I hope will get you started in the right direction. I’ve saved the file back to V5. Please have a look at the result from starting with a dished edge-otherwise you will end up with a problem area in the cutaway or if the edge is really flat enough the curvature will be ugly.
I hope you can refine the green curves now yourself to produce a recurved arch or whatever shape you like.
Normally I do not use a laminated material-I prefer to carve from solid wood and can bring the edge down flat (co-planar). But in your case I strongly suggest you consider using a radiused dish. See the violet colored layer in the attached file.
Best,
Abraham
Mbhwhitney Back_Recurve starting point suggestion.3dm (214.8 KB)
Hi Abraham - Thank you! I need to sit down and look at this in more detail.
If you’re okay with it, I may message you from this point on.
I’ve definitely picked up some tips to try out by reading this thread.
It’s really nice for us to be able to see the discussion. I hope you might consider continuing to post in this thread 
Thanks very much for posting this! I’m going to give this method a try.
I have a body outline which is nice and smooth but there are differing numbers of control points in each quadrant and the whole outline is not degree 5.
Do you also use the Surface From Edge Curves command for that narrow area along the centerline?
A make one large surface. Then use Surface split at isocurve to maintain continuity between the two.
