# Thread: Algorithm for G02 / G03 coding

1. ## Algorithm for G02 / G03 coding

Hi,

Can anybody help with an algorithm for generating circular interpolation for ARCs? I know the arc center (X,Y) the radius and the start angle and the end angle.

I want to output either a G02 or G03 gcode line.

TIA,

-James Leonard
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2. Are you just looking for a formula to find the start and endpoints? That's all you'll need to write G2 or G3 code.

3. ## I need to calculate X, Y, I and J

Originally Posted by ger21
Are you just looking for a formula to find the start and endpoints? That's all you'll need to write G2 or G3 code.
Hi,

I need to calculate X, Y, I and J (relative) for both G02 and G03, do you have formulas to do that based on the arc center, radius and start and end angles? These are values from a DXF file.

Thanks!

-James Leonard

4. You just need to find the start and endpoints using trig. I and J are the center point relative to the start point. From the little research I just did, arcs are always CCW in a dxf. It looks like you'd take the sine of the start angle times the radius will give you the Y value of the start point (relative to the center of the arc). for the X, take the sine of 90°- start angle times the radius (again relative to the center of the arc). You probably need to convert the angles from (or to) radians.

Your previous line of code needs to get you to the start point. Do the same thing to find the endpoint, which is the X,Y in your G2/G3 line.

I wrote an AutoCAD macro that outputs g-code, but it doesn't do arcs. But It will do G2 and G3 from polyline arcs. A polyline gives you the start and end points, and radius (bulge) but not the center. I find the center using a chord, and the rest is easy.

5. Originally Posted by ger21
You just need to find the start and endpoints using trig. I and J are the center point relative to the start point. From the little research I just did, arcs are always CCW in a dxf. It looks like you'd take the sine of the start angle times the radius will give you the Y value of the start point (relative to the center of the arc). for the X, take the sine of 90°- start angle times the radius (again relative to the center of the arc). You probably need to convert the angles from (or to) radians.

Your previous line of code needs to get you to the start point. Do the same thing to find the endpoint, which is the X,Y in your G2/G3 line.

I wrote an AutoCAD macro that outputs g-code, but it doesn't do arcs. But It will do G2 and G3 from polyline arcs. A polyline gives you the start and end points, and radius (bulge) but not the center. I find the center using a chord, and the rest is easy.

Hi again,

Thats good info, but I was hoping for explicit formulas. I really don't see how to calculate I and J, my math skills are not that good.

Yes, DXF ARCs are always CCW, but for CNC purposes I may need to flip them to CW. I already know how to do this and how to derive the ARC center, radius and start and end angle from three points on the ARC (begin, end and middle) but I still don't see how to do the G02 / G03 stuff.

-James Leonard

6. Find the start point of the arc using the sin method like I said. You already know the centerpoint.

I = Centerpoint X - Startpoint X
J= Centerpoint Y - Startpoint Y

7. Originally Posted by ger21
Find the start point of the arc using the sin method like I said. You already know the centerpoint.

I = Centerpoint X - Startpoint X
J= Centerpoint Y - Startpoint Y
OK!

I will give it a fly tomorrow.

-James

8. Here is an open source program to convert DXF to G-Code:

http://www.dakeng.com/ace.html

Here is my program to convert G-Code to DXF:

http://www.cnczone.com/forums/showth...?t=8814&page=2 (G-Code to DXF)

9. Originally Posted by WayneHill
Here is an open source program to convert DXF to G-Code:

http://www.dakeng.com/ace.html

Here is my program to convert G-Code to DXF:

http://www.cnczone.com/forums/showth...?t=8814&page=2 (G-Code to DXF)
Hi,

The ACE converter source code is the most difficult I have ever read. I had a LOT of trouble trying to follow the DXF load and conversion process. Also ACE won't process my DXF files (from the DXFTool for CorelDraw). So, I am trying to come to a deeper understanding of this.

-James Leonard

10. James,

Can you post a short file of the DXF format that will not work with ACE ?

Line,circle and a point.

11. ## Here is a DXF that ACE will not process

All of these DXF files are pure LINE and ARC entities. This is to improve cutting over the many shortline segments CorelDraw generates for a polyline.

Here is a circle, ellipse, star and rectangle. Both LazyCAM and SheetCAM are very happy with these DXF files.

-James

12. Could someone post the "formula" for cutting circles or circular interpolations. Just What to put in, where it all goes, and what it means. I need to cut circles and arcs.

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1. ###### What is G02 G03?
03-16-2013, 11:32 AM