DesignCAD CURVE command

[dtleahy]

Hello, (my first post here)

I used to draft professionally with AutoCAD, but always preferred my copy of DesignCAD when it came to drawing curved lines. In DesignCAD, rather than creating a bunch of arcs connected end-to-end, I am able to set up to 200 points, and a curved line is drawn through them. This is great for creating "organic" shapes, that would take a long time to create in arcs. Plotters handle the DesignCad curves just fine, but I'm wondering if the same is true for CNC...

While I dream of owning a ShopBot, I am going to have some parts cut out for me. The shapes I want to cut are sort of squiggly organic shapes that the DesignCAD curve command can draw perfectly. But, if I have to, I'll go through the painstaking process of creating the CAD file (which I guess is not really the tool path, but merely the first step in creating a tool path) out of arc segments sharing endpoints.

My question is: does anyone have experience with the DesignCAD curve output being used as CNC input? If that's not the right drafting tool to use, what software would be best for drawing organic-shaped (2D) curved lines that are going to be translated into tool paths?

Thanks!

Dennis

[gwilson]

I would try downloading a trial version of part wizard or V Carve and see how they translate. I do not know what you can export as. If dxf it might export the curves as splines. Then you might have to play with exporting options or find a way to convert them to polyline. I use a autocad lisp routine that I downloaded from www.dotsoft.com (http://www.dotsoft.com) (found out about it from the guys here).

You can get the trial version of the software above thru the Shopbot website.

Hope it helps.

Interested in other's info and your outcome with it.

Gerald

[gwilson]

just tried to go to www.dotsoft.com (http://www.dotsoft.com) and I think they are down or no longer. Sorry about that.

Hopefully someone here might have more info.

Gerald

[beacon14]

I use DesignCad extensively and use the curve command frequently as you describe. I export my part drawings as .dxf version 13 or 14, then import into PartWizard, and more recently VCarvePro, for toolpathing. I have had no problems with curves making it through the above process and toolpathing correctly. The biggest stumbling block in my experience is when lines, curves, and/or arcs are not actually connected at their ends, they may look connected but they either just miss or just overlap; the toolpathing software does funny things in these cases.

So be careful about lines, curves, and arcs ending at the same exact point, but go hog wild on the curves - I do.

[mikejohn]

Dennis
What is the difference in resulting curve when you are able to set up to 200 points, and a curved line is drawn through them and creating the same points with the AutoCad SPLINE command?

.........Mike

[rhfurniture]

Dotsoft works fine for me - try again.
Sounds exactly the same as Acad's pline, curvefit to me.

R/

[mikejohn]

rh
As I understand it, the AutoCad pline- curvefit creates the same shape as SPLINE.
Which I think (but I am not sure) is a bezier curve. It isn't arcs joined together.

..............Mike

[hespj]

Curve fit - "The curve passes through the first and last control points unless the original polyline was closed. The curve is pulled toward the other points but does not necessarily pass through them."

So it's not quite what Dennis wants.

also

"Spline curves are very different from the curves produced by the Fit option. Fit constructs pairs of arcs that pass through every control point. Both these curves are different from true B-splines created with the SPLINE command."

[rhfurniture]

Sorry John. Below pline,copied, one curve fitted.
They are all true arcs - You can explode and rejoin as a polyarc.

r/


4320

[mikejohn]

rh
at least two of the curves, the one far right, and the one right inthe middle are not true arcs, if a true arc is a segment of a circle.
Any idea what shape you get if you construcrt a SPLINE starting bottom left and clicking on the remaining 5 points in turn?

............Mike

[rhfurniture]

I've copied it, exploded one, and put every other arc on a different layer.
All come up in properties as true arcs.
Autocad's recent spline command will put a splined curve through a series of points no problem - you have to define start and end angles.
Dennis, looking back at your question, subject to translation problems that can usually be got round, any curve that can be exported as a dxf can be machined no problem.

r/


4321

[hespj]

Yes Ralph, they are all true arcs, but (and this might not be relevent to Dennis's work) they don't make a fair curve when joined together. The radius of the curve is constant until it gets to a join and then changes instantly to a new radius. Personally I don't think this is an organic shape, or a "fair curve" as boatbuilders call it. I would say a fair curve is one where the radius changes smoothly.

I'm glad to hear that newer versions of Acad now have the ability to draw splines through points. I've probably spent hundreds of hours adjusting splines to pass through points, all the time wondering why the software can't do it.

John

[hespj]

Just out of interest, here's two curves drawn in Acad and imported into Rhino. The top one is a spline, the bottom one drawn using "fit". The "graph" drawn on each curve is Rhino's "Curve analysis" of each curve, an excellent tool for getting fair curves.


4322

[mikejohn]

rh
I wrongly assumed the arcs went from one line end to another. As John says, this produces a curve which isnt 'fair'.
I can not, off hand, imagine why this method would be superior to a SPLINE (not that you have said it is superior, I just can't see when I might use it.)

....................Mike

[hespj]

Mike, one answer is "it's quick". Dennis says he has 200 points he wants his curve to pass through, and with a spline this would take a long time to get right (I know, I've done it).

Unless, as rh points out, you're using a newer version of acad. I just had a try on acad 2004 this morning, and rh is right, splines are drawn through selected points. Very useful.

[mikejohn]

John
I have some tricks for producing splines for certain applications which are fast enough if you generate the points fast.
When I have time I will post my method.
In AutoCad though, not sure what the capabilities of other CAD programs are, although I guess many have similar possibilities.

..........Mike