Curves

So, the new GCode arduino firmware supports G2/G3 arc drawing. This is all good. But is it actually useful to us beyond the 'that's neat' or 'now we support a decent amount of gcode standard X'

However, how is the host software ever going to take advantage of this fact? If we're using STL source files, any curved surfaces on the object will have already been tesselated by the design software. This isn't alwaysuseful for a reprap, as can be seen by the amount of effort required to parse, slice and sanitise triangle meshes such as those found in an STL file.

In order to take full advantage of arc drawing (less gcode output, easier to read gcode files, hopefully smoother object faces) we wouldneed some kind of constructive solid geometry source instead, letting us do the work of rendering it usefully.

- Does such a filetype exist which is actually useful to us?
- Is it worth the effort to parse and process it?
- Is the arduino firmware up for doing all the maths required for drawing curves in good time anyway?

Course, this isn't a whole lot of use for more complex curves which aren't just conic sections, but we can leave NURBS for another day

- Yes - both IGES and STEP are industry standard and have solid-body support

- No - solving the slice/dice pattern for one of these in the general case, without tessellating it first into an STL-like object, would be nearly impossible and of dubious worth.

- I'm not sure, but Zach may have a better idea.

One possible use for G2/G3 would be for the "fillet" stage of Enrique's toolchain. However, in general, I see little purpose in emphasizing support for this standard, because to me the compatibility gained from the "lowest common denominator" straight-line-only approach outweighs the smaller file size that would be the main benefit of actually implementing these standards.

i'm not sure. someone else coded the G2/G3 stuff, and i added it because i love contributions and collaboration. i'm not sure if it was intended for exclusive reprap use.

the gcode firmware has applications outside the realm of reprap. i've already used it to make drawings with a pen instead of a print head.

if you have an idea for modifying the existing code to handle arc GCodes, that would be awesome! please send me diffs and such, and i'll get them integrated if possible.

> i'm not sure. someone else coded the G2/G3 stuff,
> and i added it because i love contributions and
> collaboration. i'm not sure if it was intended
> for exclusive reprap use.

Yeah, I did the G2/G3 stuff. It was actually because I wanted to use the same hardware and electronics to do some milling and plotting, which needed the arc codes. I am sure I am not the only person to build a 3-axis positioning system first, before starting on an extruder.

In particular, this means you could use the same machine (if it's sturdy enough) to mill PCB's for the rest of the project. That is one of my forthcoming tasks...

I've recently updated the images about this project on my website (you will see why arcs were necessary) - [www.chrismeighan.com]