slicing without polygons

[marcus-wolschon 0]

Are there any slicers that accept common CAD file formats without forcing a tesselation into discrete polygons?

There are G-Codes to run perfect arcs, yet I don't see any slicer supporting file formats that can contain perfect arcs and circles that are not broken up into polygons on the way from the CAD program to the slicer.

 

[donmilne 2]

<innocent>Do you have the formula handy for calculating the bezier parameters of the curve which represents the intersection between an arbitrary 3D surface and a horizontal plane?</innocent> :wink:

Oh, also toss in this thought: in the depths of the controller where gcodes are turned into stepper motor moves, how to handle that?

Seriously, it's probably an unnecessary complication. The printer has a finite resolution. You can reach that resolution using linear moves, and you can't better it with complex curves. In the past I thought that at least the gcode file would be resolution independant, but you can achieve that in practice by levelling up to a high resolution.

 

[marcus-wolschon 0]

<innocent>Do you have the formula handy for calculating the bezier parameters of the curve which represents the intersection between an arbitrary 3D surface and a horizontal plane?</innocent> :wink:

 

Sure, this is done to render them for display a thousand times a second.

I hate seeing polygon edges in my high-res prints all the time or running onto memory limits due to the number of polygons. The finite resolution is pretty high. 30x30x30cm at 0.04mm layer height and even higher resolution in XY.

 

[donmilne 2]

Sure, this is done to render them for display a thousand times a second.

 

All software for PC that I'm aware of will convert curves into piecewise approximations, and therefore would not solve the problem posed. Just because the shader gives you a good illusion of a curved surface doesn't mean that it really has that curve.

 

[marcus-wolschon 0]

Sad.

The CAM software for my CAD does it for subtractive machining.

Thus circles can be machined with microstep-precision with a minimum of g-code.

For additive machining, the limiting factor is the STL file format. STEP, IGES, ACIS, ProE,... would be so much better.

It never is a curve. In the end it's just discrete microsteps. But that step should always happen in the machine controller when interpreting the g-code.

Projecting a 3D spline onto a 2D plane is just a trivial projection of all it's control point to this plane. In this case it's even just a parallel projection and axis-parallel too.

Bisecting a surace that is defined by 2 3D splines is just a linear interpolation of their control points. Again trivial math.