export DXF for laser cutting

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 From:  Chris (CHRIS_C)
8453.1 
Hello all. Now that I've added a laser to my workshop, I am using Moi to create DXF files for cutting. I have been noticing an issue with cutting and engraving smaller circles and other curved elements in general.

As you can see in these photos, the "stove top" circles are fairly clean, while the "knobs" for the cabinets are broken up and incomplete. I have been exporting my DXF files with polylines and an angle of 2. Is there a way to output these so there will be a greater number of smaller segments joined to create these shapes?

Thanks!

Chris
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 From:  AlexPolo
8453.2 In reply to 8453.1 
Hi Chris,

I export files for laser cutting also but I find MOI is limited in this - I use RHINO convert to ARC function prior to export. I explode all the curves and then convert any splines or small curves to ARCs. I can set their resolution in the command depending on their final size then I export to DXF using the RHINO R12 NATURAL DXF setting and I always smooth arcs and converted splines that way.

I think a similar tool or script would be required in MOI to do this.

Breaking down to really small polylines sometimes works but some laser cutting software has small limits and if it cant handle it goes wobbly.

Hope it helps.

Alex.
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 From:  Michael Gibson
8453.3 In reply to 8453.1 
Hi Chris, can you please post the DXF file for the one that had dropouts so I can see if there's anything wrong with the file itself?

re:
> Is there a way to output these so there will be a greater number of smaller
> segments joined to create these shapes?

My best guess is that you actually have too many small segments and the laser cutter control software is just ignoring ones under a particular size.

If that's the case you would probably get better results with a looser angle like say 5 degrees.

The other thing you could try is to use Edit > Separate on your rectangles with rounded corners before doing the export. That's because if an individual curve is a circle or arc it will be exported as a special CIRCLE or ARC entity in the DXF file rather than a polyline with a lot of little segments in it. If the arc is part of a longer joined curve then it will get the polyline treatment instead. I've been thinking about doing that kind of separation automatically for DXF export.

But if you could please send your DXF file I'd like to check it to see if there's any problem there.

- Michael
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 From:  BurrMan
8453.4 In reply to 8453.1 
Hey Chris,
It works pretty good on my end. It's probably the system importing the file.

We don't have an "Arc fit" yet, for what Alex is suggesting, but for your original desire, you can dice up your curves and arcs with this added script:

http://kyticka.webzdarma.cz/3d/moi/#ReconstructCurve

Be sure to launch it "Before" you select your objects, to get the options to go to polyline with a "count"....

I would encourage you to work with Michael though....
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 From:  Mik (MIKULAS)
8453.5 In reply to 8453.4 
I export DXF as a "spline" for laser cutting machine without any problem, including small circles DIA = 2,5 mm into 3mm aluminum metal sheet.

Mik
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 From:  AlexPolo
8453.6 
You will find that smaller powered lasers which are more suited to Acrylics and Sign work all handle splines and EPS based info without many problems. Its when you move into the larger industrial lasers for cutting structural steel most of these still donot accept splines and can only handle arcs and polylines in strict DXF complaint files. Even many new high powered lasers still have the same limitation.
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 From:  BurrMan
8453.7 In reply to 8453.6 
""""" strict dxf complaint files"""""!!!

Freudian slip!!! those darn dxf's! Lol
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 From:  Chris (CHRIS_C)
8453.8 In reply to 8453.3 
Hi Michael, sorry for the delay.

Here is the requested DXF.

Thanks!

Chris

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 From:  Chris (CHRIS_C)
8453.9 In reply to 8453.5 
Thanks Mik, I'll give it a shot.

Chris
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 From:  Michael Gibson
8453.10 In reply to 8453.8 
Thanks Chris, as far as I can tell there doesn't seem to be anything wrong with those DXF files, my guess is that the laser cutter software doesn't like to get lines that are too short.

- Michael
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 From:  Chris (CHRIS_C)
8453.11 In reply to 8453.10 
Thanks Michael. I'll try the polyline suggestion and see how it works.

C.
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 From:  chrisd (CHRIS_DORDONI)
8453.12 In reply to 8453.11 
Chris, can you mention the name and model of the laser system you are using?

It is possible the bundled software has the ability to generate tangent arcs from the splines within some user defined tolerance. In that case saving as a spline would be better than saving as a polyline.

The setting for the conversion may not be entirely obvious. I've worked for a few CNC manufacturers, including lasers, and sometime the software included with the machine has the functionality spread over several applications rather than being conveniently integrated.
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 From:  Mik (MIKULAS)
8453.13 In reply to 8453.12 
Hi Chris,

I remember that I had similar problem as well. Some of small circles, especilly circles with diameter less than material thickness, weren't cut correctly. Problem was solved by changing laser parametres directly in laser cutting maschine software. Producer of maschine provided to programmer "hidden" settings, so now laser beam can be slowed down before the end of finishing whole circle and therefore now it can be cut small circles into thicker materials -even 2,5 mm diameter into 4 mm Al metal plate, without changing of DXF export setting.

Hope this helps.

Mik
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 From:  OSTexo
8453.14 
Hello,

It sounds like you need a DXF file optimization program. I haven't used them but you may want to demo something like DXF CNC Graphic Optimizer or DXFTool For CorelDRAW.
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