Question about generating files for water jet cutting

My question is that hopefully someone has experience with odd little details that will help me avoid pitfalls.
I know I need to generate a dxf file from my Rhino file. Should I create my drawing in the Top view? Should I be able to use black as a line color? My drawing will be part of a circle. Is there anything special I should choose in the scheme when I export as a dxf? Do I need to do hatching to show what is solid and what is an open space?

Should I create my drawing in the Top view?

yes

Should I be able to use black as a line color?

No

My drawing will be part of a circle. Is there anything special I should choose in the scheme when I export as a dxf?

Check with the people running the water jet, these are settings i have used in the past

Do I need to do hatching to show what is solid and what is an open space?

No

Thank you so much. This gives me a start.
One more question. Is there a “standard” amount to allow for the width of the cut?

best advice is to call your water jet vendor and see what they use. Shops vary wildly with the equipment they have and the formats they can work with.

Since DXF/DWG does not support NURBS curves, and Rhino does, you’ll probably have to convert your Degree=3 and higher curves in Rhino to chains of arcs before exporting.

Your WaterJet follows G-code instructions. G-code supports three movements:
1 - Straight lines
2 - Clockwise arcs
3 - Anticlockwise arc
It’s your job to make sure you’re only send supported curves to the machine.

Lines, arcs and circles in Rhino are good to go.
Twisty Rhino NURBS curves need to be converted to arc chains. If you don’t convert them, they will be approximated by hundreds of short straight lines.

Since you need more efficient Arc objects in your DXF/DWG file, you’ll need to convert your wiggly Rhino curves to arc segments before exporting.

Use the Rhino Convert command.
Use these command option settings:
Output=Arcs
SimplifyInput=No
DeleteInput=Yes
AngleTolerance=0
Tolerance=0.01mm or 0.002"
MinLength=0
MaxLength=0
OutputLayer=Current

The tolerance controls how far the arcs will pull away from your NURBS curves. Your machining process and project will determine how much is OK. The distance is in current model units.

Then when you Export to DXF, use the “CAM Imperial” export scheme for inches and “CAM Metric” for millimeters. Both of these export simple geometry as lines and circles.

Always check your DXF file by opening it in Rhino before you send it for cutting to make sure it looks good.

Another option is to export using the IGES file format. Nearly all CAM applications support curves through IGES. Choose an appropriate IGES export option configuration for your CAM application.

Cheers

the most important piece of advice John gave here. DO NOT SKIP THIS.

Thank you both very much. My first file is a very simple thing made with circles so I should be good to go, but I’m also going to be talking with the water jet guy to verify that the file I send makes sense to him.
Thanks again for all the help.
I did open my dxf file in Rhino and it looks good.

I had been using Rhino with OMAX 2626 waterjet cutter. I believe the most different part, compared to laser, is planning the toolpath. I don’t know if it’s done by you or the waterjet technician. Generally I want to avoid closed curves and leave tiny gaps to hint the operator where the cutter should enter/exit.

I certainly have a lot to learn which I hope to learn from the folks running the water jet. Things like how sharp can corners be or should corners have a small radius and how small is small.

I’ve got a new question on this subject. If my plasma guy is using AutoCad LT should I do anything differently?

Hi -

Your plasma guy should be able to tell you if there are any issues with your files.
-wim