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Author Topic: Arc import prob in Lazy cam  (Read 7786 times)

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Re: Arc import prob in Lazy cam
« Reply #10 on: March 03, 2008, 01:56:52 PM »
Hi
I've experimented in Corel Draw 12, outputting in all its many file formats and importing into LazyCAM. I find that ellipses are rendered as octagons in some cases. This seems to be because they are output as four Bezier curves, and LazyCAM treats each of these as three straight lines. Outputting from Corel as a WMF gives the most accurate rendition - better than its own native formats. The oldest DXF formats (AutoCad 2.5, from memory) work well, but the newest are hopeless. If you see jagged lines where you expected curves, I think it's because LazyCAM isn't interpreting Beziers correctly.

Is GCode the only graphical language that doesn't support Bezier curves? It seems to me it could make for much better import of DXF and other files. The Bezier probably wasn't invented when GCode started out, but these days it is the way almost all fonts and graphics packages work.
Imagine if you could code:
Gnn X x3 Y y3 Ax By Cxx Dyy (Move along a Bezier curve to x3,y3 with control points x,y and xx,yy)
This would replace anything up to hundreds of lines of G1s.

I have written a 2D Bezier macro for Mach3, but native support would be much more elegant, so that LazyCAM could post it directly. We have all sorts of canned cycles, so why not Beziers? They are extremely easy to scale, rotate, stretch or skew and fast to draw. Much better than circular arcs which are so very restricted.

From the perspective of a CAM programme, I can see that there are some complexities, such as offsetting by tool radius. For Mach3 there might be issues of calculating acceleration and deceleration, but it could convert the curve to a sequence of G1s internally for this purpose.
Other parametric cubic splines exist with, in some cases, valuable properties, but none are as universally found in graphic files as Beziers.

As a newcomer to this business I don't know if this has ever been suggested before and, perhaps, very good reasons exist why it couldn't be done or wouldn't be worthwhile. If so, I'd love to know.

Regards
Chris Lusby Taylor

« Last Edit: March 03, 2008, 02:00:51 PM by ChrisLT »