Weird Lines When Converting pdf for Laser Cutting

[Mark Petersen]

Currently working on Emil Zarkov's (1) OV-10 Bronco in 1/32nd scale. To save my fingers I plan on laser cutting the frames. I've done this in the past with minor issues. Took the following steps.
1) Open pdf file with Inkscape.
2) Save file as as dxf.
3) Open file in AutoCAD. this so I can re-arrange frame parts and add extra slots for more. Ribs. Also holes for 1/8th dowels to keep everything in alignment. Why? Because I get a little anal at times.
Now the weird happens. The contour lines for the parts. All of them not just some are not solid lines. Instead each line is a four sided polygon of approximately rectangular shape. Curves such as the round ends of the spars and airfoil section of the ribs now consist of short or long boxes.
The only work around I can come up with is either draw completely new profiles or erase all of the extra garbage. I can deal with it if I have too.
I'm merely wondering if the problem is in an older version of Acrobat used to create the original file? Kit is 2005 vintage. Inkscape save to dxf problem? Need to update Inkscape? The CAD is 2000 or 2002.
I've done this the past with Zakov's Israeli Avara with no problems like this. I'm just curious as to possible cause.
1) I always think of him as Dr Zarkov myself.

[aansorge]

I derive cutting instructions for the laser right out of Inkscape, from the svg file.


The only time I have seen what you describe is sometimes when I use a trace routine, either the one in inkscape or the one in GIMP. I suspect that I set the contrast on the tracing tool too high or too low. If the pdf file contains vector drawings, it is not hard to select the outside trace as the cutting line and delete the rest.


I printed my last model from Inkscape as well. (I think you earlier said that you only want to cut the heavier parts, so printing is not an issue.) Something of a mistake, because Inkscape does not support ink colors (CMYK) (!) and the colors seem muddy. But Inkscape does handle the maintaining of scale better than GIMP.


Good luck, let us know how it goes.


al

[Mark Petersen]

One thing I figured out is the part outline when saved as an SVG file in Inkscape consists of a series of rectangular solid blocks arranged along a curve to represent an actual curved ed surface such as you get in an actual CAD drawing. In the DXF file what l am seeing is the outlines of these block elements. To generate new profiles I am creating the profile with either polylines or splines by picking up mid points of the lines on each end of the block element. Not something l can't work around just a pain in the rear end. My laser (a cheap Chinesium one) will run DXF files. Just have to remember to either scale by 25.4 or make sure the drawing is in Metric.
One thing I am thinking of doing is either get a different laser or laser head for more power. I can cut chipboard, card, balsa and Basswood easily enough. Illustration boards tougher. Needs multiple passes. Modeling plywood not so much. As much as I use it there is no way I could justify a CO2 laser to the boss.
One thing I would recommend to anyone with a cheap laser. Keep a notebook of with power levels (%) and cutting speed for different materials. If possible I prefer to cut at lower power and feed rates. Also if you have a return to start position place soft pads to either the laser head or the rails so that the head will not slam into the rails when returning to start. Also I mounted the machine to a piece if Baltic Birch with rubber feet and hold down clips for the material.