Re: Help! How do you CNC a solidworks spline??

I've exported hundreds of DXF files containing splines and fonts, I'm hardly confused. Fonts and splines do not translate to splines on export. They are converted to short line segments. There are no settings which can change this fact, at least not up to 2006 releases. The most efficient means I found to achieve the desired results is to trace the splines using a 3 point arc. Tedious, but using the DXF as is would result in a spline with a circumference of 12" being converted to hundreds of lines and that means hundreds of extra lines of GCode and an unacceptable finish on the cut edge.

Since you didn't reply to my direct question about your experience with SWX, I can only assume you have none, based on what you did post.

Splines in a DXF file are called splines with points on the curve given. I would suggest that the cam software does not understand the concept of splines.

Bob

0 SECTION 2 ENTITIES 0 SPLINE 5 17A 330 23 100 AcDbEntity 8 VISABLE 100 AcDbSpline 210 0.0 220 0.0 230 1.0 70 8 71 3 72 12 73 8 74 6 42 0.0000000001 43 0.0000000001 44 0.0000000001 13 0.983148089309517 23 0.182810925513346 33 0.0 40 0.0 40 0.0 40 0.0 40 0.0 40 0.5061414898570419 40 0.9199702471070123 40 1.575345136293664 40 2.045039716453304 40 2.769260067854284 40 2.769260067854284 40 2.769260067854284 40 2.769260067854284 10 13.43328730535758 20 16.85005512985181 30 0.0 10 13.58842145696185 20 16.78487631740688 30 0.0 10 13.87039558207541 20 16.66640634528891 30 0.0 10 14.34456513808076 20 16.42415660731785 30 0.0 10 14.89601632531026 20 16.49226158568692 30 0.0 10 15.40840974183308 20 16.92516579383252 30 0.0 10 15.83519929917696 20 16.65671426629983 30 0.0 10 16.07253791741661 20 16.70084606387157 30 0.0 11 13.43328730535758 21 16.85005512985181 31 0.0 11 13.89715557325682 21 16.64755713531641 31 0.0 11 14.28104652301536 21 16.49301918198279 31 0.0 11 14.93152857018393 21 16.57295260232628 31 0.0 11 15.35274227579633 21 16.78077948421505 31 0.0 11 16.07253791741661 21 16.70084606387157 31 0.0 0 ENDSEC

My conclusion, if your cam program uses the same interpolation method as your CAD program you get the expected results, If not?

Bob

Is there some confusion here? It looks, to me, like on one hand someone's talking about interpolation and on the other someone's talking about the approximation of, for instance, degree three curves with either degree 1 or degree 2 curves or their analytic line or arc equivalents.

When is a Non-Uniform Rational B-Spline not a "spline"? Is it meant that not all "splines" can be precisely represented by NURBS? Are there any in common CAx usage today or, even, since the '50s or '60s?

I see. My bad.

Yes. I do. Relatively few programs will, excluding rational second degree conic representations, create a rational Bezier or B-Spline. So when we're talking about NURBS we're usually talking about the (W = 1) nonrational forms.

But the statement was: "Nor is a NURBS curve guaranteed to be a spline.".

A NURBS curve may not be rational, it may not even wiggle, but it is always a spline.

The question was: Are there any splines [that cannot be precisely represented by NURBS] in common usage today? I should hope there are not.

'Fairly new' is fairly old by 'CAD for the common man' standards.

1995 - "AutoSurf version 2.1 for use with AutoCAD 13, integrates precise NURBS technology and Advanced Surfacing."

The MES (Solutions 3000) code was acquired in '92 making it, roughly, twenty years old.

Yes! I've seen that. I even understand the occasional bit and piece of it. ;^)

Is it?

If you know of a (we're "usually" talking) main stream 'MCAD' application that will create a rational degree 3, or higher, Bezier or B-Spline do me the favor of pointing it out.

Non-uniform knots? Compatibility? It's probably safe to say there are far more programs capable of importing rational entities without screwing them up than there are creating them, not unlike higher order entities.

"Not" as in; not a rational spline?

In "common CAx usage today"?

How do you define "fairly new" then?

Appendix K: Glossary Spline: A piecewise continuous polynomial.

We all know that has nothing to do with the four coordinate values describing a control vertex as applied to common CAx use NURBS application, right?

The question stands. Computervision "can"? Yes; CADDS, UG, Catia can. Rhino, Alias and, I assume, ICEM can. Alibre? Cobalt? Inventor? Pro/Engineer? Solid Edge? Solidworks? Any other 'main stream MCAD' programs? Or modeling packages associated with CAM software? It would be interesting information and we both stand to learn something.

You keep stumbling over that word "support", keep assuming it means more than it does.

As opposed to; by accident? Pro/E "supports" higher order NURBS; e.g. will import and interact with them. It can / will export them intact; e.g. without altering their definition. By current "design and intent" (I suppose, as PTC bought Computervision / CADDS almost ten years ago) it will not create an entity with degree greater than 3 (cubic) nor will it create a rational degree 3 entity.

And without NU that would be the ever-so-popular BS?

"The generalization of B-spline curves to NURBS (Nonuniform Rational B-splineS) has become the standard curve and surface form in the CAD/CAM industry. They offer A UNIFIED REPRESENTATION of spline and conic geometries: every conic as well as every spline allows a piecewise rational polynomial representation. The origin of the term NURBS is unclear; but the TERM was certainly a bad choice: it explicitly excludes the popular uniform B-spline curves." - Farin; "A History of Curves and Surfaces in CAGD"

And without B you have S which is all that is inferred by the term NURBS; it is going to be a spline.

Not so new that I think this tap dancing is much more interesting than, or anticipate it being more informative than "I Love Lucy" reruns or contemplating the nature and meaning of a "kernel".