How to remove duplicate lines for laser cutting?

Last week, I was getting designs laser cut on a Trotec Speedy 300. The owner of the machine said that I have to remove duplicate lines, or else the laser would cut these twice. So I removed the duplicates manually, and it was tedious. Now I wonder if there is an automated solution.

In exactly that situation you could have used CurveBoolean to get just the outline.

Sorry, I don’t understand: How would that help?

Obviously, I want not just the outline, but also the line segment highlighted in red. The only thing that should be removed is the duplicate line segment where the two rectangles touch.

In that case, you are right, it wouldn’t help.

Hi Felix- if you select both and start Trim, then click once on the duplicate area and pick either of the curve, you’ll get the right result I think. But the span there will remain part of one or the other rectangle. Splitting in ‘both directions’ and then SelDup will also work in this example. None of that is very automatic - it might be just as clean to use SubCrv on one of the rectangles.


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But I need an automatic solution. In a design I may have hundreds of duplicates. It’s easy to get lost.

Possibly -

! _SelAll _ExtractPt _SelNone _SelCrv _Split _SelPt _Enter _SelNone _SelDup _SelPt _Delete

But that will blow up your polylines- that might also be bad…



Genius solution - thanks, Pascal!

I can join them again later, which creates some rather random laser paths, but that’s fine.

Felix, The Trotec software has a cut optimizing command so that even if the lines are broken up into segments the machine should be able to cut them pretty efficiently.

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Well, I didn’t operate the machine, so I don’t know which software was used. Only I know it was a printer driver, and it definitely didn’t cut efficiently: The head was moving rather randomly from cut to cut.

For the next time I’d like to know:

  • Which software? JobControl?
  • Do you know how to enable the command?
  • Does it remove duplicate lines?
  • Trotec lasers use Job Control software, it comes with the laser. It
    works as a printer driver.
  • You enable the command by right clicking on the job when it has been put into the Job Control cut area. Pick “vector sorting” from the right click menu.
  • Nope, you’ll have to use Pascal’s clever script.
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There is a easy way to remove the overlapping lines while maintaining all lines in Rhino. Go to the top viewport, select all curves and run _Make2D. On the dialog box, select current viewport and uncheck Show tangent Lines and Show hidden lines. The result would be the same drawing without the overlapping lines.


Thanks, @nick!

That Make2D trick indeed works perfectly. Thanks @jespizua!

If you are laser cutting I would say you should really be separating your parts (depending on the accuracy required) as although the width of a laser cut is very small, there is in fact a width . In your original scenario you have two possible outcomes.

  1. Cutting outside the line (as I believe is normal practice) - One part will come out correct and the other will have a step in it.
  2. Cutting directly on the line - Both parts will come out slightly small.

I have attached an image to explain this.
Black - Original lines
Red - Width of cut
Grey - Resulting shape.

In my experience the effect that you describe isn’t really noticeable. It might be more if the shapes were staggered as you show but usually identical shapes are arranged next to each other. The laser beam has a very small diameter when focused.

That’s what the laser cutters do that I worked with in the past (Trotec, Epilog). There is no concept of inside and outside. If parts of a certain exact size are needed, then one needs to add an offset. For cutting, it is more efficient, thus cheaper, to move the parts together.

Hi @nick & @feklee

I agree with your comments, which is probably due to me not paying full attention to the initial post & looking up the type of laser cutter you are using. The laser cutter you are using is very small and low powered and yes my comments would probably not really make any difference in this case. I am used to using much more powerful cutters for metal, where the width of the cut could be more significant in the final outcome.

Hi Al,

I can concur, heavy duty laser cutters do need an offset of you want your parts to be precise.


I have a demo license for TruTops Laser and Nest lying around that I received after visiting Trumpf in Ditzingen near Stuttgart, Germany. That software package is the one used for preparing layouts to be cut into metal. Trumpf staff demonstrated it to me, but I don’t remember if one has to manually take care of adding an offset to compensate for laser beam width. If someone is interested, I could try installing it and have a look.

Anyhow, at the moment, I’m only cutting into wood and plastics.