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How can I make a negative of a path/image?

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CGT80
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How can I make a negative of a path/image?

Postby CGT80 » Wed Apr 25, 2018 8:48 pm

I have an image of an Eagle and could cut the eagle out of a sheet, but what I really want to do is cut out space around the eagle so that the eagle is part of my sheet.

I have done this once, but it is not repeatable or easy and it should be.

The software I have:
Inkscape
solid edge 2d cad
sheetcam

For the successful try, I drew a circle around the outline of the eagle. This was exported as a dxf and imported into solid edge, where I edited the lines so that just the negative space would be cut out.

The scaling when saving as dxf from inkscape is not working again. It ends up at 2000 inches instead of 11.5 inches when imported into cad. I have tried different export settings in inkscape and different settings in cad, with no luck.

What would be even better is to edit the paths in inkscape. I have played with the various options but have not figured out what is needed or what order to do them in. Instead of importing an eagle into sheetcam, I want to import the negative space/shapes to be cut out, so the eagle image is left. I would imagine it isn't a difficult process, if you know what to do. I have looked at many videos and tutorials, but haven't found out how to do this.

Any help or links to instructions on how to do this would be greatly appreciated.

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Gamelord
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Re: How can I make a negative of a path/image?

Postby Gamelord » Wed Apr 25, 2018 11:46 pm

Here's what I did. Took about 8 minutes to do.
I am sure it will require some cleanup, I also didn't check for dropouts.

1) Imported image into Corel Draw (very similar to Inkscape).
2) Un-grouped the eagle, then deleted the half circle thing.
3) grouped all the small cut-out pieces together so they didn't get lost.
4) Drew a circle around the eagle, positioned it so that it would attach to the eagle's wingtip.
5) Used the contour tool to make another perfect circle inside the one I drew in step 4. Made sure the offset was large enough to capture the wing tips.
6) Broke the contour apart, then used the trim tool to trim the smaller circle out of the larger one.
7) Deleted the smaller circle, leaving only the ring of the larger one.
8) Used the "Weld" tool, selected the eagle and welded it to the ring, attaching the wingtip to the outer ring piece.
9) Used the "Trim" tool to trim out the smaller pieces grouped in step 3 from the larger portion of the eagle.
10) Deleted the smaller pieces, leaving the eagle with the pieces cut out attached to the ring.
11) Exported as SVG and JPG, posted up on here.

Hope that helps.

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CGT80
Posts: 11
Joined: Tue Sep 26, 2017 12:25 am

Re: How can I make a negative of a path/image?

Postby CGT80 » Thu Apr 26, 2018 12:29 am

Thank you for testing that and posting directions.

It looks like you made almost exactly what I did to test the image to see if the details would show up with my plasma (I added a loop at the top for a string to hang it), but for my project it needs to be opposite.

I am building a garden hose holder and the back of it will be a sheet bigger than the eagle, and I will cut out the white spaces that are in your image, leaving behind the eagle as part of the sheet. Maybe your method will do that, but it appears reversed. Edit: I imported your svg into sheetcam, and it does work. The colors are reversed in the jpg image you posted, and it threw me off. Now I have two different ways to do images this way. :D

I searched google with the term "negative space." A tutorial showed up and it worked.

Others may have the same problem, so I will post what worked.........at least to make the part in sheetcam. It should cut fine.

The tutorial: https://youtu.be/X9Weag1lxUc
From this svg, I chose path and break apart
clicked on the circle and set path to no color and fill to black and then 20% to get gray
shift, clicked on the circle then the eagle outline and path difference. The eagle turned white.
shift and selected each interior detail (to be cut out) and then chose no stroke and black fill.
changed the gray circle (what is left of it) to black and saved image as svg.

The black portions will be cut out, leaving the white eagle and the white background (the back of my hose hanger).
The hose hanger is drawn in cad. In sheetcam, the negative space from the eagle is set on top/inside the back of the hose hanger.

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Gamelord
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Re: How can I make a negative of a path/image?

Postby Gamelord » Thu Apr 26, 2018 11:16 pm

Awesome, glad it worked out for you. That should be a fine hose hanger.
Once you take flight, your eyes will forever be turned to the sky." "Lack of appreciation is the worlds biggest crime."

Torchmate 6x14 w/THC Downdraft
Thermal Dynamics Cutmaster 101
Corel Draw / Adobe Illustrator
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