Used or using OpenSCAD for precision machining?

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Used or using OpenSCAD for precision machining?

Cory Cross
Hi all,

I'm a programmer and love everything that can be done via descriptions
and compiling. I used gEDA for printed circuit boards and usually create
the footprints via emacs. So obviously, I like OpenSCAD.

But... it can't export circles. I just made up a model really fast of a
motor shaft coupler. But the round areas just aren't round. I'm hoping
for a couple thousandths (~0.08mm) precision.

So, does anybody know if just cranking up the precision ($fs/$fa) is
enough if I send out the job to be made?

Or should I be trying to learn something else, like PythonOCC?

Thanks,
Cory

ps Judging from some archive reading, I suppose if OpenSCAD moved its
backend from CGAL to OCC it would be able to export IGES or STEP and
have real circles.

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Re: Used or using OpenSCAD for precision machining?

nophead


On 16 February 2012 06:40, Cory Cross <[hidden email]> wrote:
Hi all,

I'm a programmer and love everything that can be done via descriptions
and compiling. I used gEDA for printed circuit boards and usually create
the footprints via emacs. So obviously, I like OpenSCAD.

But... it can't export circles. I just made up a model really fast of a
motor shaft coupler. But the round areas just aren't round. I'm hoping
for a couple thousandths (~0.08mm) precision.

It takes surprisingly few facets to get good precision. The points are bang on the circle and the flats shrink inwards by a factor cos(180 / n). So if your motor shaft is say 5mm to be within 0.08mm cos(180 / n) has to be more than 4.92/5  which makes n only about 18 I think.

So, does anybody know if just cranking up the precision ($fs/$fa) is
enough if I send out the job to be made?

I don't see why not, or use the formula above to set $fn = 180 / acos((d - 0.08) / d).

The eye is quite sensitive to facets, due to the change in reflected light intensity of the different angles. That means you could be well within tolerance and when viewed looking at the circle it would look perfectly round, because you would not notice an 0.08mm error. When viewed from the side you may well be able to see the facets though. In which case you have to set $fa to quite a low angle, or increase $fn.


Or should I be trying to learn something else, like PythonOCC?

Thanks,
Cory

ps Judging from some archive reading, I suppose if OpenSCAD moved its
backend from CGAL to OCC it would be able to export IGES or STEP and
have real circles.
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