Using OpenSCAD for CNC milled aluminum jobs

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Using OpenSCAD for CNC milled aluminum jobs

jdabbs003
Hello, I have three parts in OpenSCAD, and am interested in having them fabricated by a job shop using a CNC milling machine.

No one seems to work off of CSG files, and the bottom line is OFF and STL files really end up throwing away a lot of information regarding arcs and holes.  For that matter, no one supports OFF anyway for CNC machines.

So, how can I get from OpenSCAD to STEP or IGES, to get these parts fabricated?

(one caveat, these parts use imported DXF's, generated by another CAD program, which are then extruded, rotated, translated, and combined in OpenSCAD.  DXF arcs seem to blow up FreeCAD which would have been an easy way to do this.  When I load any of the CSG files into freeCAD, they are unrecognizable).

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Re: Using OpenSCAD for CNC milled aluminum jobs

nophead
There are no true arcs in OpenScad so STL throws nothing away apart from truncation of numbers to float. You simply have to set $fa and $fs appropriately for milling.

On 28 October 2014 18:50, jdabbs003 <[hidden email]> wrote:
Hello, I have three parts in OpenSCAD, and am interested in having them
fabricated by a job shop using a CNC milling machine.

No one seems to work off of CSG files, and the bottom line is OFF and STL
files really end up throwing away a lot of information regarding arcs and
holes.  For that matter, no one supports OFF anyway for CNC machines.

*So, how can I get from OpenSCAD to STEP or IGES, to get these parts
fabricated?*

/(one caveat, these parts use imported DXF's, generated by another CAD
program, which are then extruded, rotated, translated, and combined in
OpenSCAD.  DXF arcs seem to blow up FreeCAD which would have been an easy
way to do this.  When I load any of the CSG files into freeCAD, they are
unrecognizable). /





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Re: Using OpenSCAD for CNC milled aluminum jobs

Stefan Göttsche
I would be interested in the same.

As far as I understand, the 3D format exportable in OpenSCAD is not readable by my local mill/lathe shop per se.

I would therefore either like to convert them to a readable 3D format, or export views to DXF. This is something OpenSCAD can do (haven't tried yet),
but I have read that the generated DXF files use no circles or arcs as there are none in the OpenSCAD innards.
I have yet to see how this functions regarding rounded edges, of which I have quite a lot in some parts.
The minimum would be exporting some views to 2D DXF and making some 3D view/screenshot to accompany it, but it would probably generate extra work for the mill shop.






On 28. okt. 2014 19:56, nop head wrote:
There are no true arcs in OpenScad so STL throws nothing away apart from truncation of numbers to float. You simply have to set $fa and $fs appropriately for milling.

On 28 October 2014 18:50, jdabbs003 <[hidden email]> wrote:
Hello, I have three parts in OpenSCAD, and am interested in having them
fabricated by a job shop using a CNC milling machine.

No one seems to work off of CSG files, and the bottom line is OFF and STL
files really end up throwing away a lot of information regarding arcs and
holes.  For that matter, no one supports OFF anyway for CNC machines.

*So, how can I get from OpenSCAD to STEP or IGES, to get these parts
fabricated?*

/(one caveat, these parts use imported DXF's, generated by another CAD
program, which are then extruded, rotated, translated, and combined in
OpenSCAD.  DXF arcs seem to blow up FreeCAD which would have been an easy
way to do this.  When I load any of the CSG files into freeCAD, they are
unrecognizable). /





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Re: Using OpenSCAD for CNC milled aluminum jobs

Taylor Alexander
I did CNC machining for many years. Machining anything from OpenSCAD is awful, because it doesn't preserve any of the original lines of the part. It would be very difficult to accurately machine anything that originated from OpenSCAD, even if you convert it to a format the machine shop can read. The exported format is simply not good.

In this case, the best thing you can do is make drawings of the part to give to the shop, and they can re-model it in their preferred cad program. You might just want to make those drawing from scratch rather than try to export them, because again OpenSCAD doesn't support smooth arcs and doesn't properly preserve the lines (someone correct me if I'm wrong).

OpenSCAD would be perfectly capable of exporting for machining if it supported IGES and true arcs. IGES is apparently CSG compatible and is on the OpenSCAD roadmap, but has been there for years. I am a big fan of the idea of OpenSCAD supporting IGES, because then it could export high quality models to programs like solidworks. Sadly, there doesn't seem to be any interest in this internally.

On Tue, Oct 28, 2014 at 12:30 PM, Stefan Göttsche <[hidden email]> wrote:
I would be interested in the same.

As far as I understand, the 3D format exportable in OpenSCAD is not readable by my local mill/lathe shop per se.

I would therefore either like to convert them to a readable 3D format, or export views to DXF. This is something OpenSCAD can do (haven't tried yet),
but I have read that the generated DXF files use no circles or arcs as there are none in the OpenSCAD innards.
I have yet to see how this functions regarding rounded edges, of which I have quite a lot in some parts.
The minimum would be exporting some views to 2D DXF and making some 3D view/screenshot to accompany it, but it would probably generate extra work for the mill shop.






On 28. okt. 2014 19:56, nop head wrote:
There are no true arcs in OpenScad so STL throws nothing away apart from truncation of numbers to float. You simply have to set $fa and $fs appropriately for milling.

On 28 October 2014 18:50, jdabbs003 <[hidden email]> wrote:
Hello, I have three parts in OpenSCAD, and am interested in having them
fabricated by a job shop using a CNC milling machine.

No one seems to work off of CSG files, and the bottom line is OFF and STL
files really end up throwing away a lot of information regarding arcs and
holes.  For that matter, no one supports OFF anyway for CNC machines.

*So, how can I get from OpenSCAD to STEP or IGES, to get these parts
fabricated?*

/(one caveat, these parts use imported DXF's, generated by another CAD
program, which are then extruded, rotated, translated, and combined in
OpenSCAD.  DXF arcs seem to blow up FreeCAD which would have been an easy
way to do this.  When I load any of the CSG files into freeCAD, they are
unrecognizable). /





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Re: Using OpenSCAD for CNC milled aluminum jobs

mario taricco
In reply to this post by jdabbs003
Yo can use PyCam
http://pycam.sourceforge.net/
PyCAM is a toolpath generator for 3-axis CNC machining. It loads 3D
models in STL format or 2D contour models from DXF or SVG files.

Il 28/10/2014 19:50, jdabbs003 ha scritto:

> Hello, I have three parts in OpenSCAD, and am interested in having them
> fabricated by a job shop using a CNC milling machine.
>
> No one seems to work off of CSG files, and the bottom line is OFF and STL
> files really end up throwing away a lot of information regarding arcs and
> holes.  For that matter, no one supports OFF anyway for CNC machines.
>
> *So, how can I get from OpenSCAD to STEP or IGES, to get these parts
> fabricated?*
>
> /(one caveat, these parts use imported DXF's, generated by another CAD
> program, which are then extruded, rotated, translated, and combined in
> OpenSCAD.  DXF arcs seem to blow up FreeCAD which would have been an easy
> way to do this.  When I load any of the CSG files into freeCAD, they are
> unrecognizable). /
>
>
>
>
>
> --
> View this message in context: http://forum.openscad.org/Using-OpenSCAD-for-CNC-milled-aluminum-jobs-tp9977.html
> Sent from the OpenSCAD mailing list archive at Nabble.com.
> _______________________________________________
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Re: Using OpenSCAD for CNC milled aluminum jobs

jdabbs003
In reply to this post by jdabbs003
Looking at the csg file content, it seems like it has all the geometry info.  It's a text description of the DXF files transformed and combined, which implicitly means all the arcs and lines in the DXF file are preserved.

But, looking at the responses (thanks!), here is my take away:

1. OpenSCAD is really intended for 3D printing but not CNC jobs.

2. OpenSCAD geometry is polyhedral mesh only, no arcs or circles.

3. For CNC with OpenSCAD, I need to convert the part to STL, then someone needs to convert the STL to G-Code.  (Honestly, this seems like a recipe for disaster when it comes to tolerances and flatness.)


I also have two follow-up questions:

1. Is there no other program that can read the CSG file and come up with it's own geometry?  (FreeCAD blows these parts up).

2. Is there any other OpenSCAD type platform that I can use to programmatically create these parts, but output CNC-friendly files instead of STL?
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Re: Using OpenSCAD for CNC milled aluminum jobs

Johannes Reinhardt
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi,

> *1. OpenSCAD is really intended for 3D printing but not CNC jobs.

It is not that 3D printing could not benefit from a non-mesh input
representation, but the current tools are working mostly with stl
input.

> 2. OpenSCAD geometry is polyhedral mesh only, no arcs or circles.

Internally no, but the stl export yes. As you mention the csg, which is
a dump of a internal representation, still has arcs and co.

> 3. For CNC with OpenSCAD, I need to convert the part to STL, then
> someone needs to convert the STL to G-Code.  (Honestly, this seems
> like a recipe for disaster when it comes to tolerances and flatness.)*

You probably could crank up the accuracy of the stl up until it doesn't
matter for all practical purposes. But it is certainly not ideal.

> I also have two follow-up questions:
>
> *1. Is there no other program that can read the CSG file and come up
> with it's own geometry?  (FreeCAD blows these parts up).

FreeCAD is the only one I know, and seems like a good solution,
because it allows to save to a "smarter" format like step or IGES.
However, it doesn't support some special constructs (minkowski and
hull were a problem, at least some time ago). If you don't use those,
this sounds like a bug, and you could try to work with shoogen on the
FreeCAD forum to fix it. http://forum.freecadweb.org/

Greetings

Johannes

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Re: Using OpenSCAD for CNC milled aluminum jobs

tp3
In reply to this post by Taylor Alexander
Taylor Alexander wrote
Sadly, there doesn't seem to be any interest in this internally.
Just curious... on what facts is that statement based?
-- Torsten
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Re: Using OpenSCAD for CNC milled aluminum jobs

nophead
Does IGES support hull and minkowski? If not I can't see how you can ever preserve the true arcs. They only exist in circle, cylinder and sphere in the source code. As soon as you operate on them they are converted to straight segments.

On 31 October 2014 15:00, tp3 <[hidden email]> wrote:
Taylor Alexander wrote
> Sadly, there doesn't seem to be any interest in this internally.

Just curious... on what facts is that statement based?



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Re: Using OpenSCAD for CNC milled aluminum jobs

Whosawhatsis
For 2D hull/minkowski, it should be relatively simple to convert to a path on a 2d plane (which can then be extruded).

I'd be happy even if OpenSCAD only supported true arcs in 2D, with DXF export, and converted them to segments for everything else the way it does when you import a DXF with arcs.

On Friday, October 31, 2014 at 8:11 AM, nop head wrote:

Does IGES support hull and minkowski? If not I can't see how you can ever preserve the true arcs. They only exist in circle, cylinder and sphere in the source code. As soon as you operate on them they are converted to straight segments.

On 31 October 2014 15:00, tp3 <[hidden email]> wrote:
Taylor Alexander wrote
> Sadly, there doesn't seem to be any interest in this internally.

Just curious... on what facts is that statement based?



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Re: Using OpenSCAD for CNC milled aluminum jobs

Stefan Göttsche
As it is, I will just design all the parts in OpenSCAD, and then look at the exported DXF. I will have to do several corrections anyway as there are no means to specify tolerances (eg. H7).
I will maybe have to draw parts of the DXF anew, but the design process was so much faster in openSCAD that it is worth it.


On 31. okt. 2014 20:18, whosawhatsis wrote:
For 2D hull/minkowski, it should be relatively simple to convert to a path on a 2d plane (which can then be extruded).

I'd be happy even if OpenSCAD only supported true arcs in 2D, with DXF export, and converted them to segments for everything else the way it does when you import a DXF with arcs.

On Friday, October 31, 2014 at 8:11 AM, nop head wrote:

Does IGES support hull and minkowski? If not I can't see how you can ever preserve the true arcs. They only exist in circle, cylinder and sphere in the source code. As soon as you operate on them they are converted to straight segments.

On 31 October 2014 15:00, tp3 <[hidden email]> wrote:
Taylor Alexander wrote
> Sadly, there doesn't seem to be any interest in this internally.

Just curious... on what facts is that statement based?



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Re: Using OpenSCAD for CNC milled aluminum jobs

tp3
In reply to this post by Whosawhatsis
Whosawhatsis wrote
I'd be happy even if OpenSCAD only supported true arcs in 2D, with DXF export, and converted them to segments for everything else the way it does when you import a DXF with arcs.
How could that work even for easy things like "difference() { square(10); circle(8); }"?

The difference is mesh based and DXF does not support CSG directly as far as I can see in the format documentation.
-- Torsten
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Re: Using OpenSCAD for CNC milled aluminum jobs

Whosawhatsis
The CSG function would have to perform the boolean operation, creating an arc from the segment of the circle's circumference and joining it with the lines of the square, just like it currently does with the segment of the n-gon's perimeter. It might require a different/modified CSG engine if the current one can't handle it, but I thought someone mentioned at some point that CGAL had some support for 2d curves that wasn't currently being used by OpenSCAD...

I don't know how difficult it would be, I'm just saying that it would be a really useful feature to have available.

On Friday, October 31, 2014 at 1:10 PM, tp3 wrote:

Whosawhatsis wrote
I'd be happy even if OpenSCAD only supported true arcs in 2D, with DXF
export, and converted them to segments for everything else the way it does
when you import a DXF with arcs.

How could that work even for easy things like "difference() { square(10);
circle(8); }"?

The difference is mesh based and DXF does not support CSG directly as far as
I can see in the format documentation.



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