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Small and complex things

Discussion in 'SketchUcam 'Most wanted Feature'' started by inventorArtist, Nov 2, 2015.

  1. inventorArtist

    inventorArtist New Member

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    One issue I run into a lot is when making a small and complicated item I often get errors.

    This snippet for example gives the error in NCPlot "R value is too small, minimum R is 0.006".

    G01 Z-0.0875 F7
    X7.1333 Y8.1986 F20
    X7.1149 Y8.2185
    X7.1167 Y8.3392
    X7.0839 Y8.3763
    X7.0854 Y8.4848
    X7.3643 Y8.4796
    X7.3542 Y8.2569
    X7.2070 Y8.2275
    G03 X7.19532 Y8.22446 R0.00030

    My remedy is to go around the drawing looking for small radius arcs and chopping them out with the line tool or increasing the radius.

    Could there be a way of finding arcs that will cause a problem?

    Also I find that on inside cuts if the cut line ever intersects itself then it wont cut. So I have to go around and look for places where it will intersect. Can there be a feature to automatically fix this or allow the cutter to intersect itself?
     
    inventorArtist, Nov 2, 2015
    #1
  2. swarfer

    swarfer Moderator Staff Member

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    NCplot is complaining but is your CNC controller complaining? some will , some won't (-:

    There are several solutions to this:

    1: select all the (small) arcs, right click, select 'explode'. this transforms all the arc segments into line segments and you will not have any issue with R since they will all be output as G01 commands.

    2: OR, when you create the arcs in the first place, use fewer segments. so for a fillet you can use 2 or 3 segments, it will look rough in the drawing but the gcode will use real arcs and be smooth. if you do this, do not explode the arc!

    3: if your drawing has a lot of small line segments (having done {1} above) both Gcode generation and Gcode cutting will take a long time. If the line segments are less than 1/4 of the bit diameter, you probably cannot see them anyway (-: so, how about simplifying the drawing? you can do this with the EdgeTools2 plugin ... http://sketchucation.com/forums/viewtopic.php?t=24593
    use the 'Curve Simplification' function.... note that you have to remove faces for this to work (but phlatten will put them back for you)
    you need to experiment with this and see what gives you good results because it depends a lot on the bit size.

    There is no automatic solution for intersecting cuts because Sketchup automatically splits lines that cross. I have no way to detect that and the inside/outside routines rely on having single complete loops which allows them to sort the lines into a good cut order.
    You can use centerline cuts instead, just do a manual offset line, and set it as a centerline. Centerlines don't care about crossovers, but the cut order may be quite odd, again because of the way Sketchup presents the lines to SketchUcam which is very hard to solve, I have tried several times already.

    4: stop using NCPlot (-:
    the real issue is with the internal precision of the math. calculating arc segments uses sin and cos and doing those on very small numbers creates floating point over or under-flows. if the program uses double precision floats then this is less of a problem.

    5: SketchUcam could refuse to output very small arcs and auto convert them to line segments. doable but not now, I need a holiday!
     
    swarfer, Nov 3, 2015
    #2
  3. swarfer

    swarfer Moderator Staff Member

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    btw can you post an example sketchup file for me to look at?
     
    swarfer, Nov 3, 2015
    #3
  4. generalsocial

    generalsocial New Member

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    I like NCPlot since when it crashes in there it usually crashes on my cnc. So it saves me a lot of cutters.

    Also you can do really cool stuff. Like if you click jog line, it positions the editor to the line of code in question. So I just go to the previous line and I can adjust the height to avoid fixture collisions. I keep all the safe heights low to save time but some of them need to be raised. So I do this manually.

    Now that you've got the Z down jog running at high speed in the new version, I may be able to just set the safe height a bit higher and avoid this extra step.

    I think I see what is causing trouble occasionally. Arcs which are not very small are being depicted as a bunch of smaller arcs. But they are flipped over so the arc is very pointy. They look normal in the drawing but the gcode is a bunch of tiny arcs. I just delete the large arc and redraw it and the new cut lines render better.... I wonder what's causing that?
     
    generalsocial, Nov 5, 2015
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  5. swarfer

    swarfer Moderator Staff Member

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    no idea. I tried yesterday to generate arcs with radii less than 0.006" and it is surprisingly hard to do in Sketchup. They end up being very very small and indistinguishable from a straight line in the real world. Just explode those arcs into lines, they will a) work and b) cut faster
     
    swarfer, Nov 6, 2015
    #5

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