Arc Tolerance Issues

Greetings! I believe I am having an arc tolerance issue which is creating a problem with my final cut. I will do my best to explain.

I’m using Adobe Illustrator to create a perfect tesselation. A tesselation (if you don’t know already) is a shape that can fit into itself infinitely - so the angles on each side to be be perfect. In illustrator the design is spot on. Each side is the same arc - just flipped and rotated. I recently noticed that after I import my .dxf file into sheetcam, that sheet cam is adding vector points that are not in the original design…BUT sheetcam is NOT adding these vector points in the same spot on each arc. This is a detail I observed after I noticed my cnc router cuts were slightly off - which defeats the purpose of having a CNC router in the first place. The tesselation isn’t fitting together as smoothly as I would like and I’m thinking these new vector points might have something to do with it? Can anyone guide me on this arc tolerance thing? I played with the settings but didn’t get better results.

What is the best way to import my .dxf arcs into Sheetcam and have it be exactly the same as the original? There is a possibility this could be an issue with my CNC table itself - but for process of elimination I’ll keep this particular conversation focused on sheetcam.

I do notice if I stretch my design and import it - that the vector points are pretty spot on in comparison to the original. But it’s too big.

Any feedback is very appreciated.

Thank you in advance!

Could you send me a drawing to look at.

I looked at your drawing. The issue is that your curves are not circular arcs. G-code can only understand lines and circular arcs so SheetCam has to break these curves up into something g-code can handle. First SheetCam breaks the curves into thousands of tiny line segments then it tries to find areas where the lines are close to an arc. Those areas are converted to arcs. The rest are left as lines, with some segments removed. Obviously all of this conversion introduces some errors. Go to Options->application options->drawing import and change the minimum segments for arc fitting to something like 20. This means that at least 20 segments have to fall on an arc for SheetCam to convert them. You also may want to decrease the arc fitting tolerance. The smaller you go the more accurate teh result but the more segments you will get. You also may want to decrease the maximum detail reduction error. After making changes reload your drawing to see the results. You will have to experiment a bit to get a balance between accuracy and code size.

Is there any downside to getting more segments?

Depending on your machine having more segments can really slow down cutting. It also slows down SheetCam when generating tool paths and creates bigger g-code files.

Machine controllers vary widely. Basically you need to find settings that suit your application the best.

Thank you!!