Post-processing 3D contour as G2/G3 (arcs) is not working on a large stock

[Anonymous]

I'm having big issues with getting Fusion 360 to export a 3D contour as G2/G3 arcs in post-processing when my stock is large and my origo, therefore, is far away from the 3D contour operation.

I've made 2 example files that illustrate the issue. In the first one, the stock is 100mm x 100mm, and as you can see the circular paths are detected:

The generated G-code contains G2 and arc operations for the circles:

If I increase the stock size to 400mm x 600mm and keep the same operation, then the circular paths are still detected:

But the outputted G-code contains no G2 or G3 operations, but instead changes the arcs to a lot of small lines:

My postprocessor is the Stepcraft UCCNC postprocessor, but I believe this is an overall issue with Fusion 360. I've attached the 2 examples below so you can play around with them yourself.

I'm kind of stuck with the issue and my CNC is running very slow and jerky when the arcs are converted into lines. What's the reason for this problem occurring and what can I do to get around it?

[Anonymous]

I've figured out a solution to the issue. If I set the tolerance and smoothing to 0.001, then arcs will be created instead of linear paths.

It seems counter-intuitive to me that arcs would be created if I set a smaller tolerance and smoothing rather than increase it. Can anyone explain to me why that's happening?

[boopathi.sivakumar]

The reason is when the tolerance is loose then there is a possibility toolpath will create it as a spiral arc (The start and end radius of the arc is different) due to the tolerance.

The moment you tighten the tolerance the start and end radius will be the same so it considers as an planar arc.

This can be controlled in the post processor by adding a property named which will allow the post to support for spiral arcs

allowSpiralMoves = true; // << allow spiral arc