Closed Polylines export

anbar

Hi all,
I am designing some items in Sketchup Pro from which I will have some parts cut by laser.

For this I am exporting the sketchup file to .dwg or .dxf and it all works fine (i colour the edges by editing materials colour edges, blue, red or black) , however, the cutting service have said that the lines need to be 2closed polylines" for the laser to cut all along a line, at the moment the lines are 'not closed' meaning that the laser stops at the end of every little line (section) then restarts again, causing problems.

Is there any way to export with "closed polylines" or a plugin to do the same?

I have searched for closed-polylines however it seems to crop up mostly to do with importing into sketchup from CAD, rather than the other way around.

Help, as always, appreciated.

Anbar

d12dozr

...just a thought... What if you weld the lines together before export? http://www.smustard.com/script/Weld

Trogluddite

Hi Anbar,
This is something that drives me nuts too - I design in SU for the laser machine that we have at work, and to be fair, often have similar problems with "native" AutoCAD files that we get sent in.
Another common problem I've found is that often each individual 'segment' is a closed curve in its own right, even for strictly 2D drawings and 'welded' shapes - so the laser will cut every segment twice over, and that really makes a mess!

First thing I would advise is to ask your laser service what (if any) other vector file formats they support. I have found for our machine (uses "LaserCut5" controller software) that Adobe Illustrator files (.ai) are the most reliable - which sadly, SU does not support, leading to the following workaround...

First I export individual faces as SVG files using the SU plugin from FlightOfIdeas, then import those into CorelDraw for "tidying up", from which I export them as .ai files. CorelDraw is a bit expensive, but I have heard on the laser forums that the freeware vector program InkScape can do this too.

Using extra 2D software as a 'middleman' is a bit of a pain, but it does offer a few advantages too...

Easy to check if curves are closed; only closed curves will fill with colour (but remove fills before export as many laser machines don't understand them properly).
Simplifies layout of 2D parts to make best use of the materials.
The opportunity to replace SM 'segmented' curves with true vector curves for neater shapes (I put a small shape at the curve centres in SU to help with this).

Still far from ideal, but despite a lot of posting on laser machine forums, I have yet to find a better way - I would be very glad to hear if anyone has a simpler method (time to learn some Ruby I guess!).

anbar

D12dozr: weld works in SU, but when you export the lines are no longer "welded".

Thanks Trog,

I downloaded the trial of AutoCAD and ahve edited the files in that, closed-polylines etc and will see waht the cutting service make of that. Very expensive program though so once the trial ends I'm not sure what to do.

I will take a look at Inkscape and see if that does the trick: I'm not too bothered about having to use a secondary program if "all i have to do" is close lines. SU is so much easier to design in I cant see myself trying to learn a new package (like autocad or Corel etc) ... the designing of 3D objects in SU is second-nature for me now...and changing those into 2D sections is simple.

If only i could export them whole!

Trogluddite

You're welcome.
I quite agree - I experimented with the demo's of quite a few CAD packages when we first started making our own hardware at work. IMHO, the speed and simplicity of modelling in SU more than compensates for the hassle of export "tweaking". (plus we have the friendliest and most helpful user forum, and all those incredible Ruby guys "upgrading" the software on a daily basis! Hint, hint )

Here's a few other little tips that may help when designing for laser...

The 'underside' of parts will have a slightly wider kerf due to the way that the laser is focused. So export your outlines looking towards the side where the dimensions are most critical, especially for thick materials (> ~3mm).
If cutting or engraving text, always convert to vector outlines, as fonts often do not translate well.
Don't be tempted to butt parts up against each other to save space; leave a gap of a mm or two. 'Shared' cut lines will often get cut twice, and can spoil the edge of the first part if it moves slightly after being 'released' from the sheet.

Many small laser firms these days are using cheaper imported Chinese machines, and the software for these is often rather arcane and works in non-standard ways - for example our "LaserCut" software treats colours as different 'layers' but doesn't recognise genuine layers within the source file.
As a designer, how are you supposed to know this? So it seems odd to me that the guys who program the machines do not offer to optimise files at their end - a reasonable fee for an 'expert' to do this could be cheaper than paying the designer to spend hours revising their files until they hit on something usable!

Hope your project comes out well,
Trog.