Increasing/decreasing outline size by a specific offset

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Increasing/decreasing outline size by a specific offset

Bare with me if this is a stupid question (and it probably is), but what is the most elegant way to shrink/extend an object so its outline is by a certain amount larger/smaller than the current one?

I can achieve this either by scaling, but calculating the factor can be tricky and I'm concerned that the resulting coordinates are not precise (i.e. 2.9998 instead of three). I also helped myself by constructing the new outline with parallel lines etc., which results in an exact outline but is a lot of work.

As a background: I'm creating outlines for laser cutting (not cutting myself though but sending them to Formulor where they accept only SVG). Since I now that the kerf will be e.g. 0.2mm for a certain thickness, I want to compensate this by increasing/decreasing the ideal outline by this amount.

Husky
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Re: Increasing/decreasing outline size by a specific offset

Hi Oxdeadbeef - welcome in the forum!

Just to be sure that we are talking about the same thing: You are looking do create something like this "red dash" line around the white given shape for a CnC job?

Husky-2014.08.10-01.png (15.69 KiB) Viewed 2191 times

If not - could you please attach an example dxf. Thanks.
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Re: Increasing/decreasing outline size by a specific offset

Yep. Just not on both sides.
Simplest example: I want to cut a circle from e.g. a transparent material (layer 1) and insert it in a hole in an opaque material (layer 2). Since I know that the CO2 laser will create an kerf of ~0.2mm, I want to reduce either the hole size or increase the circle size by by 0.2mm to compensate the kerf.
Now for a circle this is easy. For a complex object though, I didn't find an elegant way to do this yet.

Husky
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Posts: 1283
Joined: Wed May 11, 2011 9:25 am
Location: USA

Re: Increasing/decreasing outline size by a specific offset

0xdeadbeef wrote:For a complex object though, I didn't find an elegant way to do this yet.

Ok - understood. For simple entities like a line or a circle the "Line tool" / "Parallel with distance" would do the job.

For more complex objects I would recommend to get familiar with the use of Polylines. You can create a shape in first place as a Polyline or you can create a Polyline based on a Selection. The nice thing about a Polyline shape is - you can use the Polyline Offset Tool to handle easily the needed offset to compensate the kerf of a CO2 Laser etc. etc. etc.

Check this out (yes I know - it's ugly!):
Husky-2014.08.11-01.png (50.24 KiB) Viewed 2177 times

Try this for yourself:
Load this drawing and play around with the Polyline / Offset tool (Menu -> Draw -> Polyline -> Offset). An additional Option-bar will pop up and you can put in the correct value for the kerf.
test.dxf

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Re: Increasing/decreasing outline size by a specific offset

Ah, that's exactly what I searched for - but the "polyline from segment" thing was hidden to deep and located in a menu (draw) where I didn't expect it.
But ok, that seems to work just great. Thanks!

Sorry for bugging, but while converting shapes into polylines something weird happened in one case. See appended screenshot. The outline and the rectangular section where merged into one polyline. I don't quite understand how this could have happened as obviously this can't be one polygon and I understood a polyline can't contain intersections!?
Attachments
polyline.png (3.45 KiB) Viewed 2171 times