[QueueJr]

Hey all, I need some help.

I am using RhinoCAM 2012 and I have been unable to toolpath a profile of a round object using arc interpolation (G02 or G03 command) rather than the software approximating a curve using a series of straight segments (G01 linear commands).

I have tried adjusting the Tolerance value in Cut Parameters of the toolpath to increase the accuracy of the approximation, but I cannot make the line segments small enough to make the part to spec. I am using the provided post processor for Haas (my machine is a Haas TM1). In the post processor editor I see a place to specify that G02 and G03 pertain to arc commands, but nowhere to specify how the software chooses to toolpath arcs.

Can anyone tell me how I might be able to profile a round object with arc interpolation rather than a linear approximation?

[swarfman]

This thread is a little old but it's a good question. In some of the 2D tool paths you'll see the option to "ArcFit" the tool path and an option for the tolerance. In 3D operations I normally open the MOp and right click the toolpath. This will open a g-code list with icons at the top. Click the rounded "Arc" to open the Arc Fit dialog to set your parameters. You can set the tolerances and axis you want it to look at, run the arc fit, observe the results, undo them and try again until you're happy with the results.

The $20 question is how to make it work. Say the original tool path was created with an intol/outtol of .001. When you ArcFit you'll need to loosen it up to at least .002 so there's some room for it to calculate the arcs. If you're not getting all the interpolated arcs you want, try loosening up the arc fit tolerance to say .003 or .004 to give the software a better opportunity to include more of the tool paths. The software is fitting the arcs onto the existing tool paths so there's some tolerance stack up to consider when doing this. You'll see it in the finished part the most when calculating arcs from a vertical to horizontal surface like when you've used a Parallel finishing MOp on a complex object. It works the best when your MOp's are done correctly for the object you're machining i.e. finishing the arc's of the object with their own MOp's and arc fitting those individually, then machine the horizontal/vertical surfaces separately and arc fit those accordingly.

Also, if you think it should be arc fitting a curve and it won't - turn on flat shade in your current Rhino window to see the faceting and what the curves on the part really look like. In some cases it's necessary to create a smoother custom mesh for the part to remove the faceting, then hide the Nurbs object and run your tool paths on the smoother mesh.

It takes a little practice to understand it and get it right, but it works. It seems like it's actually a bit better in the 2012 version than it was previously.