. .
  1. #1
    New poster here with a Dxf2Gcode question....

    I have just started CNC cutting with an eShapeoko. Very lightweight stuff - cutting balsa sheet and possibly thin ply for the set of model boat plans that I design. I have a lot of plans in Ashlar-Vellum format, which I can get into DXF and then use Dxf2Gcode to create toolpaths. And I have two problems:

    1 - the GRBL running on the eShapeoko Arduino controller does not do tool radius correction. At the moment i can minimise the problem with a sub-mm cutter so the error is not great, but I would still like to do things properly. Is there any way to do this with what I have, or do I need to change the controller?

    2 - the Dxf2Gcode produces workable G code, but the Z axis goes up and down like a yo-yo. This seems to be an issue with filling in the correct Z axis defaults. Dxf2Gcode has 5 fields for the Z axis - retract depth, slice depth, work origin, safety margin and final depth. There appears to be no explanation of what these do on the net - I filled in likely figures and ended up with a bouncing z axis, which I have to manually edit to get sensible runs. If anyone here uses Dxf2Gcode and knows how to set these properly I would be grateful for a hint....

  2. #2
    So.... no one uses dfx2gcode then?

    In that case, can anyone suggest an open source package that does the same job which DOES come with instructions?

  3. #3
    I don't use the program,but would it solve your problem to offset the shape by the tool radiusand to use the resulting shape for the tool centreline trajectory?

    I do use Freecad and find it great I also find it occasionally exasperating.It does deal with tool offsets and allows a variety of tool entry options.

  4. #4
    Very kind of you to respond!

    My problem is that I have many existing plans in Ashlar-Vellum CAD format. I want to use these, rather than redrawing years of work in a different package I'm not familiar with.

    In theory G-Code has simple commands for off-setting the cutting line by the tool radius. But I' bought an eShapeoko, which uses an Arduino running GRBL, and that only supports a cut-down set of G-code - no tool radius compensation.

    My options seem to be to change the Arduino for a bigger processor which supports a better GRBL set, or find a Cad-G-code interpreter which has compensation.... DXf2Gcode said it supports it - but just seems to add G41/2.

  5. #5
    The G41/2 are doing what they should by appearing.I think you will have to find a way to add the details of the tool you are using to a tool library so it has a figure to work with.I don't use the program myself but I do expect that it needs the information in order to apply the correct amount of compensation.Otherwise the computer wont know whether you are using a 25mm dia tool or a 1mm.

  6. #6
    I have added the tool radius size. The problem is that the Arduino GRBL does not support G41/2. So Dxf2gcode adds the request for compensation, and Grbl ignores it. GRBL on an Arduino cannot do tool compensation, so it will either have to be done elsewhere before loading the Gcode, or I will need to use a different piece of hardware to drive the mechanics - a Raspberry Pi, perhaps, with a different set of code...

  7. #7
    I became curious after reading the last post and while I can't claim to have an easy answer,I did generate a toolpath for GRBL for a bit of a learning tool for myself.I generated a hexagon in Freecad and hope that both the .nc file and the screenshot will appear below.As you will see the tool radius compensation has been applied to the tool centre line data and there is no G41 or G42.

    Click image for larger version. 

Name:	hexagon toolpath.jpg 
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ID:	25544

    Just the edited highlights of the toolpath:

    N240 (begin operation: Profile_Edges)
    N250 (Path: Profile_Edges)
    N260 (Profile_Edges)
    N270 (Compensated Tool Path. Diameter: 6.0)
    N280 G0 Z11.0000
    N290 G0 X65.1841 Y63.9240
    N300 G0 Z9.0000
    N310 G1 X65.1841 Y63.9240 Z0.0000 F180.00
    N320 G1 X71.8109 Y60.0981 Z0.0000 F480.00
    N330 G2 X73.3109 Y57.5000 Z0.0000 I-1.5000 J-2.5981 F480.00
    N340 G1 X73.3109 Y22.5000 Z0.0000 F480.00
    N350 G2 X71.8109 Y19.9019 Z0.0000 I-3.0000 J-0.0000 F480.00
    N360 G1 X41.5000 Y2.4019 Z0.0000 F480.00
    N370 G2 X40.6851 Y2.0793 Z0.0000 I-1.5000 J2.5981 F480.00
    N380 G2 X38.5000 Y2.4019 Z0.0000 I-0.6851 J2.9207 F480.00
    N390 G1 X8.1891 Y19.9019 Z0.0000 F480.00
    N400 G2 X6.6891 Y22.5000 Z0.0000 I1.5000 J2.5981 F480.00
    N410 G1 X6.6891 Y57.5000 Z0.0000 F480.00
    N420 G2 X8.1891 Y60.0981 Z0.0000 I3.0000 J0.0000 F480.00
    N430 G1 X38.5000 Y77.5981 Z0.0000 F480.00
    N440 G2 X41.5000 Y77.5981 Z0.0000 I1.5000 J-2.5981 F480.00
    N450 G1 X65.1841 Y63.9240 Z0.0000 F480.00
    N460 G0 Z11.0000
    N470 (finish operation: Profile_Edges)
    (begin postamble)
    N480 M5
    N490 G17 G90

    The challenging part might be to import your .dxf's into Freecad to experiment with and my experience is that they can come in as dozens,even hundreds, of entities that need to be joined together.I am quite a novice with Freecad and might not be aware of a way round this sort of thing and one may well exist.There are a few post processors included with Freecad and I selected GRBL.

    If you do elect to switch to a Raspberry Pi,what will you run on it?

  8. The Following User Says Thank You to routerdriver For This Useful Post:

  9. #8
    That looks like an approach which is well worth trying! I shall have a look at FreeCad and see how easy it is to use. Thanks for that.

    I have not researched driver software to run on a Pi - that was just a possible way ahead. There may be bigger Arduinos which can be used. All of my electronics are in a small box mounted on the X gantry, and I was hoping to keep them there...
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	electronics.jpg 
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ID:	25545  

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