Rhino DXF output

[catsketcher]

Hello all,

I have been off boat building and finishing the design of my 7 metre folding cat. I got some panels laser cut and the DXF files had my gentle curves made out as straight lines. I didn't pick this up as my old version of Autocad can't load DXF and only saw the problem when I picked the initial parts up.

Thankfully I didn't get all the parts made up or I would have had a really big stuff up on my hands. I will have to get two sheets redone. So the message for those of you who are new to CNC is to carefully check you DXF outputs and do a test piece before you hand over all your costly panels.

To the experts I ask a question - what parameters do I have to use on the DXF output options tab in Rhino to get a nice curvy DXF file and is there a DXF viewer I can get cheap?

As to the thread on tired of Cad I can sympathise. I seem to have a love/ hate relationship with my computer. It can produce lovely looking shapes but sometimes it takes so long to do it. I remember getting awfully down though when I wrongly cut a piece of ply or had to redo a whole days work when I stuffed up in boatbuilding. The curse of the easily bored is to constantly find new things to learn. That said I wouldn't want it any other way.

may your lines be fair

Phil

[CGN]

hi Catsketcher,

I guess you send your CNC files as a DXF and you would like to make sure that the tolerances of the DXF are ok, then you can do this:

1, Make a copy of the original file to convert
2-Type "ConvertToPolyline"
3-This will ask you for an "angle" value, here use 20 to start
4-Type "CrvDeviation" and check how much the difference between the original curve and the original curve is, half a millimeter could be a good reference.
5-if it works then you have a polyline that follows the original curvature with a minimal deviation and you can save as a DXF, if it does not work then go to step 2 and change the value of the angle.

I like this option because instead of saving the file and then checking if the dxf was created correctly IMO takes a little bit more time.

and for a DXF viewer, AutoCAD "DWG TrueView" reads DXF and DWG, I think it can read any version of AutoCAD.

Also eDrawings works fine and is a good alternative to DWG Trueview

On general thi sis a good information on Rhino Meshing options

http://www.thermoanalytics.com/suppo...esh-rhino.html

[Raggi_Thor]

There is also a setting in Rhino when you export to dwg and dxf, maximum angle, I think.

[Chris Ostlind]

Hi Phil,

I've had the same issues in the past and here's how I got to a very good solution.

For argument's sake, let's say you have already done the, Unroll Developable Surface action on your hull panels and have created some type of nesting arrangement to fit the material shapes from which you will be cutting.

A) Select everything and project to cplane in the top view

B) Use DupBorder on the surfaces and then delete the intial surfaces leaving just the borders

C) Use the settings below when you go to the dxf save. They show-up in the header on a prompt page as AutoCAD export options

AutoCAD Version: Release 12

Save Curves as: Polylines
Use Bulge Arcs box is checked

Save surfaces as: Polygon Meshes

[Chris Ostlind]

Sorry hit the wrong key too soon.

Hi Phil,

I've had the same issues in the past and here's how I got to a very good solution.

For argument's sake, let's say you have already done the, Unroll Developable Surface action on your hull panels and have created some type of nesting arrangement to fit the material shapes from which you will be cutting.

A) Select everything and project to cplane in the top view

B) Use DupBorder on the surfaces and then delete the intial surfaces leaving just the borders

C) Use the settings below when you go to the dxf save. They show-up in the header on a prompt page as AutoCAD export options

AutoCAD Version: Release 12

Save Curves as: Polylines
Use Bulge Arcs box is checked

Save surfaces as: Polygon Meshes

Save Polygon Meshes as: Polyface meshes

Curve Options: Project to Plane checked
project to cplane checked
Use simple entities checked

Simplify tolerance: 0.05
Polyline max angle: 10
Polyline chord height .01
Polyline seg length 0


This will give you clean arcing curves in your dxf output to the CNC machine and yield beautiful straight panels that will join nicely when you stitch them together.

Say hi to your brother for me.

Chris Ostlind

[burakreis]

>and is there a DXF viewer I can get cheap?

does free is cheap enough? if so, take a look at;
http://www.progecad.com/

btw, latest service packs for rhino(3) have some important dxf,dwg export fixes? don't miss them if you do.

[catsketcher]

I very much appreciate the responses from the forum. I have another load of marine ply coming and will test my outputs before cutting these sheets up. The laser cutter is a good option. It gives a very clean cut and the width of less than 1mm per cut means you can really tighten up the nesting. Hopefully this time things will go right.

The only reason I am doing the CNC process is because I want to sell plans for my little folding cat (www.foldingcats.com) . I want the builders to be able to get a stack of parts so they can start assembling right away. It has taken me much more time than I will save to produce a computer generated parts list than if I did the whole thing the old way and lofted but I hope to save time for future builders. Here's to hoping there will be some.

cheers

Phil

[Clinton B Chase]

This was helpful for me. I wanted to bring this back with a question.

I notice that the export process breaks up a curve into many polylines, sometimes an enormous number that may slow down CNC cutting.

Any tricks to reducing this effect and make machining go faster?

[DCockey]

To export NURB splines from Rhino 4 in .dxf format as splines rather than segmented lines use the 2004 Natural export scheme.

[Clinton B Chase]

And so it is just a question about whether my cutter can deal with splines. He has a 2011 Auto Cam software. Should be fine?

So what is the advantage of exporting as splines vs polylines? The DXFs I am using (for the next couple jobs) are all polycurves currently. They come from a designer's Rhino file.

[DCockey]

Splines are smooth. Polylines are joined straight segments.

If the software can import splines then they would be better, because the operator and/or software can decide how to divide the spline for efficient cutting rather than having to deal with many short straight segments.

Not sure what you meant by polycurve.

[DCockey]

Could not find any reference to Auto Cam 2011 software. Did you mean 2011 AutoCad or something else?

AutoCad 2012 can import .3dm files directly from Rhino. Don't know when that capability was added.

[Clinton B Chase]

Well, we still struggle with issues with cutting to DXFs. Interestingly the issue (i.e., machine stops in mid cut) seems to happen with the lines and arcs. The curves which are exported as polylines run OK (I thought those would be the issue, but are not as far as I can tell).

I can't see a break in lines in my DXF file, yet the machine will still stop. In the attached file, the U shaped geometry just would not cut, stopping close to where lines turned the corner at the arcs.

I seems that something is happening, and it is intermittent and not very predictable, to the files in transferring from my program to his.

My cutter is redrawing trouble geometry in his CAM software (he told me the name of it but I forget everytime I post), but I very much would like to know what is going on so his drawing time doesn't eat into my slim margin.

Any ideas would be great.

[DCockey]

Originally Posted by Clinton B Chase

.......

I can't see a break in lines in my DXF file, yet the machine will still stop. In the attached file, the U shaped geometry just would not cut, stopping close to where lines turned the corner at the arcs.

.......

Attached file?

[Clinton B Chase]

Here it is.