Convert DXF polyline arc to gcode from the bulge

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I am writing an application in VB.net to convert a DXF file to GCode for my GRBL laser. I know there are many free or low cost programs out there, but I want this program to work in a very specific way (for too many reasons to explain here). I have been working on this program for about 6 months and am at my last "step".

I need some help converting the Arc segment of a Polyline to GCode (using G02 or G03).

By standard, the DXF stores the arc segment as start point, end point, and bulge. So I have these 3 variables. I know that the radius of the arc is 4*Atan(bulge), so I can figure the angle of the arc. What I need is how to convert this to GCode (or .nc file) using G02 or G03. I know that a +bulge is counterclockwise, and -bulge is clockwise, so that's no big deal.

But now what? G02 and G3 requires the center of the arc... but how do I get it? Is there another way of going about this?

I would be very, VERY grateful for any help here. Thank you!

What I have tried:

Google search, DXF-to-GCode Converter, Autodesk Fusion 360

Posted 2-May-18 15:16pm

Ronald Veldman

Updated 6-Jul-23 0:00am

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Marcus Neves · Answer 1 · 2021-03-11T07:35:00

Here in C# ...

C#

public static List<LinhaGCode> Bulge2IJ(double X1, double Y1, double X2, double Y2, double Bulge, Config config)
        {
            double C = 0; //lunghezza della corda - length of the cord
            double H = 0; //altezza del triangolo - height of the triangle
            double alpha2 = 0; //mezzo angolo di arco  - half arc angle
            double beta = 0; //angolo della corda rispetto agli assi - orientation of the segment
            List<LinhaGCode> lista = new List<LinhaGCode>();
            double I, J, R;

            if (Bulge != 0)
            {
                C = Math.Sqrt(Math.Pow((X2 - X1), 2) + Math.Pow((Y2 - Y1), 2));
                alpha2 = Math.Atan(Bulge) * 2;
                R = Math.Abs(C / (2 * Math.Sin(alpha2)));
                H = Math.Sqrt(Math.Pow(R, 2) - Math.Pow((C / 2), 2));

                if ((Bulge > 1) || ((Bulge < 0) && (Bulge > -1)))
                {
                    alpha2 = alpha2 + Math.PI;
                }

                if (X1 != X2)
                {
                    beta = Math.Atan(System.Convert.ToDouble(Y2 - Y1) / System.Convert.ToDouble(X2 - X1));
                    if (X2 < X1)
                    {
                        beta = beta + Math.PI;
                    }
                }
                else
                {
                    if (Y2 < Y1)
                    {
                        beta = (-1) * (Math.PI / 2);
                    }
                    else
                    {
                        beta = Math.PI / 2; ;
                    }
                }

                if ((Bulge > 1) || ((Bulge < 0) && (Bulge > -1)))
                {
                    I = (X2 - X1) / 2 + (Math.Cos(beta - Math.PI / 2) * H);
                    J = (Y2 - Y1) / 2 + (Math.Sin(beta - Math.PI / 2) * H);
                }
                else
                {
                    I = (X2 - X1) / 2 - (Math.Cos(beta - Math.PI / 2) * H);
                    J = (Y2 - Y1) / 2 - (Math.Sin(beta - Math.PI / 2) * H);
                }
                if (Bulge > 0)
                {
                    lista.Add(new LinhaGCode("G03", X2, Y2, config.Z_G03, I, J));
                }
                else
                {
                    lista.Add(new LinhaGCode("G02", X2, Y2, config.Z_G03, I, J));
                }
            }
            else
            {
                lista.Add(new LinhaGCode("G01", X2, Y2, config.Z_G01));
            }
            return lista;
        }