Open Source CNC Torch Table from OSE (Open Source Ecology)

[Elifarley]

Marcin from OSE (Open Source Ecology) has recently asked for help regarding the conversion of DXF to G-Code for the open source CNC torch table (see more at http://blog.opensourceecology.org/2011/12/100k-from-the-ewing-marion-kauffman-foundation/):

[...] the above machine meets our criterion of simple design. Our goal is $2k for a 6×10 foot machine  comparable to industry standards costing about $40k. This requires toolchain integration of toolpath g-code generation and use with an open source CAM package such as LinuxCNC. Our last experience with the tool chain was messy, so if you are a Python programmer, help us integrate existing modules into a killer Open Source CNC Torch Table Control Software package. See previous work here and referring page here. Considerations include height control feedback integration, piercing strategy, and tool width corrections.

One of the OSE members created a PHP script that reads the output of dxf2gcode and makes some changes to it, as explained at http://opensourceecology.org/wiki/DXF_to_G-code_Conversion_Tutorial#Piercing:

As it stands, the toolchain for open source torch cutting is quite disintegrated. It turns out that the above code, while in principle correct, does not address the practical considerations of piercing metal. For example, when one wants to torch out a hole - one should not pierce the metal right on the cutting line, because piercing is a messy operation. Instead, one wants to pierce inside a hole, and subsequently move to the circle contour. Moreover, one wants to preheat the metal not by standing in place, but oscillate back and forth to heat the metal more evenly.

It further emerges that the fuel flow rate should decrease after metal ignition, as the fuel gas is important primarily in preheating, not in cutting.

Moreover, the width of the cut needs to be considered, so the actual toolpath needs to be modified by about 1/16 smaller diameter size for circles when using a #2 cutting tip. Thus, finetuning is a precise matter - if one is interested in precise cuts such as small bolt holes.
To address the proper piercing issue, Vann Miller has written a correction script. This script does 3 things. First, it takes out the z values generated by the DXF to G-code Converter (not needed in a 2-axis motion system at hand). Second, it starts a pierce by moving towards the center of a hole. Third, it rotates the torch around a small radius (.05") during preheating. The number of rotations is currently 8, but one should be able to modify this. 

 

 

A better approach could be to implement these changes as options for dxf2gcode. Any thoughts on this?

Thanks,

Elifarley

[Christian Kohlöffel]

Hello Elifarley,

 

i personlly dont see any problem implementing changest to dxf2gcode. The code is available at google. code and if required i can give anyone rights to open a new development branch to integrate this changes.

 

If you need help just let me know  ...

 

regards

Christian

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[Elifarley]

Hi Christian,

Which revision number should I use as a starting point?

Thanks!

[Christian Kohlöffel]

Hi,

 

just use this one:

http://code.google.com/p/dxf2gcode/source/browse/branches/dxf2gcode_b02_tkinter_development/

 

thats the newest development branch with the tkinter GUI Kit. The trunk is still under heavy development with a new Graphical User Interface based on pyQT which is totaly different ...

 

If you want to use the Google Code SVN Server i can give you account and make a branch for your development. You just need a Google Account first.

 

regards

Christian

----- Original Message -----

From: Elifarley

To: dxf2gc...@googlegroups.com

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[Elifarley Callado Coelho Cruz]

Hi Christian,

I find it easier to work with Mercurial, so I cloned the SVN repo to https://bitbucket.org/elifarley/dxf2gcode

(I'm currently asking people for help with this, as I'm short on time to do it myself)

Thanks,

Elifarley

2011/12/10 Christian Kohlöffel <christian-...@t-online.de>

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Elifarley Cruz

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