I have used Fusion to create a sculpture with several 4-sided hollow bodies. The sculpture will be made with thin sheet metal. I need help creating DXF files of the unrolled/flat templates for laser cutting. The curved surfaces include twists that are not compatible with Fusion Sheet Metal features. I want to use Rhino 8 on a Mac to flatten the surfaces with no deformation to make DXF files for laser cutting. I have used the following process:
Created shell bodies of each surface and confirmed with curvature analysis in Fusion that they are âdevelopableâ (i.e. Gaussian curvature =0).
Saved each surface as a STEP file in Fusion
Imported the STEP file into Rhino
Used Rhino UnrollSurface command to create flat template geometry.
Iâm looking for help with selecting the unrolled geometry and creating DXF files for export. I would like to import the files into Fusion so I can make reduced scale paper drawings and small paper model prior to the full size sheet metal sculpture. See attached sample STEP file from Fusion. This is my first time to ever use Rhino.
Any help would be appreciated. Thanks.
UnrollSrf used on this surface returns a warning/comment in Command Line History: âArea is 0.3147 sq inches (0.20 % ) bigger after unrollingâ. This is because your surface is not developable. The surface is a ruled surface but is twisted. While every developable surface is a ruled surface, not every ruled surface is developable. Your surface may or may not be close enough to developable for your purposes.
If a surface is developable then one of the principle curvatures will be zero. In Rhino principal curvatures of a surface can be measured at a location on the surface using the Curvature command. Circles will be displayed corresponding to the principal curvatures at that point. for example:
Thank you for the good lesson on Gaussian curvature.
Iâm probably going way off topic, but any advice you may have on the following would be appreciated.
ExplodeBlock: After importing the T4.step file, I couldnât select the surface when using the ExplodeBlock command. However, using the selection filter with only polysurfaces checked, confirmed that it was a polysurface. This appears to be no problem.
UnrollSrf with Explode=No, works well on most of my surfaces that are all green with Fusion curvature analysis.
Export command: Iâm using trial and error testing out all of the various combinations of settings (see below). Any recommendations on the following settings?
Clean up Flat Pattern in Rhino: When importing the DXF into Fusion, Iâm getting âissuesâ like lines, extending beyond edges, and lines not connecting to edge lines, resulting in non-closed faces within edge boundary. ChatGPT said to clean up in Rhino prior to exporting using Join command. Any recommendations?
Curvature Analysis Command: I couldnât get the curvature analysis command to work with the attached T3b surface. It also would not UnrollSrf even though Fusion shows it is all green in Curvature analysis. It also would not show results of Squish command. Any recommendations?
Gray object on gray background made it very difficult to see the object but finally found it. Selected the object and ExplodeBlock Changed the objectâs color.
Curvature Note: the object is a polysurface. Curvature only works on one surface at a time. Click on a different portion of the object to analyse other parts.
Depending on the CNC process it might be preferable to convert the splines to lines and arcs first. Although there is an Export Scheme for R12 Lines & Arcs, there is better control over the conversion to arcs if DupBorder / DupEdge is used to extract the curves, then Convert curve to arcs.
After smoothing out some of my surfaces, I was having success using the information you both provided. I used ExplodeBlock. UnrollSrf - I had to increase the Relative Tolerance to 0.02. I deselected âShow surface isocurveâ, and exported to Fusion using 2018 Natural with good results.
I thought the process was going to work for all of the smoothed surfaces. However the attached STEP files would not âunrollsrfâ even though the Rhino curvature analysis showed all green. Any thoughts would be appreciated.
Command: _Open
Successfully read file âE:\Downloads E\H2.3dmâ
1 open polysurface added to selection.
Command: UnrollSrf
Calculating starting area⌠Press Esc to cancel
Select curves, text dots, and points on polysurface to unroll ( Explode=No Labels=No KeepProperties=No )
Calculating starting area⌠Press Esc to cancel
Three surfaces unrolled.
Area is 0.8083 sq inches (0.86 % ) smaller after unrolling
Creating meshes⌠Press Esc to cancel
Thank you for sticking with this topic. I may need to refine my question and post a new topic?
I canât seem to duplicate your UnrollSrf results. When you selected the surface for âUnrollSrfâ did you use a selection filter? I disabled the selection filter.
I could only get the UnrollSrf command to work when I set the Relative Tolerance to 0.09. It resulted in distorted flattened object s. They were very similar to the distorted objects (H1 and H2) from your process. Notice that your flattened objects are simplified and straightened out at the end with corners. It does not match the original shape with curved edges. I also see that the âunrolledâ area was 0.86% smaller. Considering how good the curvature analysis looked I was surprised with the distorted edges and the area discrepancy.
Can you think of any way to improve the STEP mesh prior to unrolling to fix the distortion.
Here are the steps I followed to unroll the objects in your .3dm files.
Downloaded the .3dm file.
Open the file in Rhino 8
Clicked on the object to select it.
ExplodeBlock command
UnrollSrf command
Clicked on the object to select it.
In response to âSelect curves, text dots, and points on polysurface to unroll(Explode=Yes Labels=No KeepProperties=No)â clicked on âExplode=Yesâ to change it to âExplode=Noâ.
Right click and the command completes
The unrolled surface is not visible.
Zoomed out and panned until I found it near the Cplane origin.
Used the Windows Snipping tool to capture the image I posted.
SaveAs a file with the unrolled surface which I then posted.
Not need to change any tolerance, etc.
My quess is you are doing something else.
Do you have experience with other CAD software? How much have you used Rhino? Are you assuming experience with other CAD software carries over directly to Rhino? If so there may something simple that works differently in Rhino.
As I explained above it is very possible and common for surfaces which are not developable to have Guassian curvature values with very small but non-zero magnitudes.
When I use the UnrollSrf command and then try to select the object, I canât select the object. If I select the object first and then enter the UnrollSrf command, the comand line jumps back to blank.
Iâm a total beginner and have only been using Rhino and Blender for about 10 days trying to figure this out. My only other experience was using MeshMixer to unwrap the Fusion generated STL surfaces of a 4â tall kinetic sculpture. I now know that it was a lucky miracle that I managed to weld the distorted surfaces together.
Iâm gaining confidence with Fusion to perform only the specific work flows required to make my sculptures. I started to hire a freelance 3Dcad expert on Upwork to do the unrolling, but stopped when I determined it would be thousands of $. Iâve learned a lot from your comments. Thanks
Just to add a couple of practical things about prepping DXFs for CNC workâŚ
Various CAM softwares have varying ability to handle different inputs. Commonly you will find, especially if your CNC shop is using DXFâs, that they will need the file to ONLY have lines and arcs. Polylines, Circles, Rectangles, etc are not ok.
You can check your lines with the âWhatâ command. It will return a lot of details, near the bottom look for âValid Curveâ and âArcâ or âLineâ. If you get Polyline or Spline then try âExplodeâ on the shape to break it down.
It helps when checking your geometry, and especially when starting out, to âjoinâ your lines to confirm that you have a âclosed shapeâ and that the intersections are actually connecting.
One helpful technique is to use âCurveBooleanâ (with DeleteInput=All) to make sure you have no overlapping segments and clean intersections. You can then explode this to return it to lines and arcs.
Another visual way to check your work is to use the hatch tool with a solid fill to confirm that the lines are intersecting and that you have a closed shape. If the Hatch fails, your lines are not intersecting.
One last easy check is to upload your DXF file to an automated estimator, like SendCutSend or Xometry. The robots will let you know if your file is bad and sometimes will give you an idea of what to fix.
And, since you talked about scaling, although CAD and CAM can handle tiny line and arc segments, the actual machines can have real trouble with too many very small sequential segments as it will effectively stop in place while trying to execute tiny moves one by one (a great way to start a CNC router fire). All that to say, scaling something detailed down for testing may introduce some troubles. Itâs best to try to keep the total resolution of the shape as large as possible.
cdordoni
David Cockey
