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A nifty work-around for HeeksCNC Kurve offset error

HeeksCNC can be finicky about profiles.  Often I've found that a sketch which should be easily profiled won't generate any gcode at all.  When I look in the console, I find an error like this

  File "/usr/lib/heekscnc/", line 247, in profile
    raise Exception, "couldn't offset kurve " + str(offset_curve)
Exception: couldn't offset kurve <area.Curve object at 0xb6f4bf2c>
It most often happens when profiling inside a closed sketch where the radii is close to the diameter of the cutter.  Sometimes I can get around it by changing from climb to conventional milling or vice versa.
Recently I was profiling several cutouts that were exact copies of one another just rotated around a central point.  Some of the cutouts would profile fine and others wouldn't  I emailed Dan Heeks the author of the software and he clued me in to a work-around.
It seems that the error is coming from the entry point.  By simply setting a new start point for the profile close to the middle of the longest span, the error magically disappears.
This won't work in every case, especially if the pocket is very close to the size of the cutter or made up of tight curves but for the most common cases it should work fine.  Thanks Dan!

HeeksCNC pocketing problem.

A user on the #cam IRC channel had a problem pocketing a shape in HeeksCNC. I've been stung by this myself. In the first picture below you can see the six identical pockets have not pocketed the same. The user had designed the oblong shape and copied and was confused why all the copies didn't pocket the same way.

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If we pan the view we see additional geometry below.

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The user had designed this part in another package and imported the file to HeeksCNC. The user is designing and building a 3d part in the sense that it has real depth to it, but for all practical purposes, this pocket operation is really a 2d (actually 2.5d) operation. Since both the top edge and bottom edge of the oblong shape are included in the sketch along with the vertical lines connecting them, HeeksCNC was getting confused trying to order the segments to create a closed sketch. After we realized this, the user deleted the lower level of the geometry and reordered the sketch. Everything worked perfectly after that.

The thing to remember is that in pocket operations, the depth of the pocket is controlled by a parameter of the operation and not by the geometry of the drawing.

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Problem with imported dxf files

I've seen this before and suspect that it has to do with the spline curve being converted to little line segments.  If the their are gaps, HeeksCNC doesn't profile correctly.  I've been able to fix it, but it usually involves quite a bit of manual work in qcad to get the segments right.