Tidying up surfaces in igs file?


#1

Hi, again apologies that I’m a bit of a novice with Rhino. I’m using Rhino and Madcam to create model aircraft moulds.

I’m in Australia and a modelling colleague in the UK has helped me by drawing up a new wing design which I want to work on in Rhino. He’s a CAD professional and used Catia, and sent me the file as an iges file. I can import it OK and it looks good, but I am having trouble working with it. (attached)Wing.igs (1.5 MB)

He and young family are moving house right now so I don’t want to bother him too much!

I need to be able to select the edge of the wing shape, right on the tip of the leading edge and half of the depth of the trailing edge, as the parting plane line and the reference for toolpaths. When I’ve drawn up wings in Rhino I’ve had a distinct edge to work on, but this drawing doesn’t seem to have surfaces following that edge all the way round.

I also need to have the model completely closed with no naked edges, so that it can be successfully Boolean subtracted from a solid to leave the negative shape.

Can anyone give me some advice on how I would tidy this up (without losing its accuracy) or does it need to be saved differently?

I only just noticed “OpenNurbs” and wondered if that was something that would be useful in sending such files from other programs for use in Rhino? I will never be a CAD expert, so I am always likely to be using drawings from other guys who use programs like Catia, 3Dmax or Solidworks.

Thanks, Andrew


(Menno Deij - van Rijswijk) #2

There’s some bad objects (SelBadObjects command) in the drawing, running over the leading edge.

Also, the wing can’t be closed due to, in part, these bad objects and modeling inaccuracies (as compared to the tolerance). Even with 0.1 mm tolerance (100x higher that in the file), the wing won’t close due to edges having inconsistent surface normals. You can use the Dir command to make the normals consistently point outwards. Then joining may be more successful.

OpenNURBS is the geometry “engine” on which Rhino is built. The 3dm file format is defined in OpenNURBS and is completely open and accessible to others as it is open source.


(Pascal Golay) #3

Hi Andrew - the edges are off at the very tip of the wing-

  • I retrimmed the top and bottom surfaces at the tip to one another there, see the different shape compared to the original at the white arrow

  • there are some very very skinny surfaces at the leading edge that are only just slightly more than tolerance wide- these need to be Untrimmed. (Blue arrow)

  • I matched (MatchSrf) for Position the upper wing surface to the upper tip surface (Cyan arrow), with Refine checked. These edges did not want to join.

  • I also replaced the planar surfaces on the trailing edge.

-Pascal

Wing_PG.3dm (417.0 KB)


#4

If the goal is to make a mold and your parting surface is predefined (from the original profiles)., then maker the parting and build everything matched to the parting. Also since it looks like this has symmetry, I would just build one side and use mirror to create the other.

The 2 problem areas in the file are where there are small sliver surfaces and the tip. I would get rid of both. The area with the sliver can be fixed by extending the surface and trimming back with the parting surface. For the tip I cut out a rectangle area that can be easily filled with a 2 rail sweep.
WingMold.3dm (711.7 KB)


#5

Menno, Pascal, Jim, thank you very much. Pascal and Jim I feel humbled that you’ve actually completely fixed the drawing for me! This is all I need to go ahead now and get ready to cut the shapes. But I have a lot to learn about using these various commands. I’d like to have a tutorial with someone showing me what you guys actually did - although I can follow you, I lack the experience to know how to decide what methods to use to fix problems.

If I draw the wing myself I keep checking as I go along that the various surfaces are joinable and that there are no bad objects or naked edges. I have the CNC machine but since I’m not expert at Rhino and I know several experienced CAD guys who are aeromodellers, it is likely that over time I will have these other guys drawing up projects for me to cut. One of my main contacts uses Catia, and the other one uses 3DMax. In general terms, can you give us any advice on how to avoid problems like these bad surfaces when they create a file for me to use? I’m not sure how I’ll handle the meshes created by 3DMax.

Sincere thanks,
Andrew


#6

Hi Andrew,
One thing you might try with Catia is to use STEP formatt instead of IGES. In my experience that is less likely to have problems. I have no experience with 3dMax so I can’t tell you anything there.

-jim


#7

OK thanks Jim.

Could I digress a little and ask for a tip on a related issue …

The airfoil .dat files originally have a trailing edge that tapers together (no thickness at TE). But on our moulds, we need a certain TE thickness to allow some material thickness (composite cloth) to be laid over the TE area. We use a number of foils along the tapering wing for the loft or rail sweep, and despite their different scales they all must have the same TE thickness.

The way I’ve dealt with this is rather tedious … I take the airfoil shape (have to interp cv from points and rebuild and simplify it as it has a large no. of points … that’s another story) and then split it into top and bottom halves. For eg a TE thickness of 0.5mm, along the trailing edge line on the plan shape, I create a thin rectangle extending above and below the cplane by .25mm. I then take each foil half, copy and move to its position on the wing plan line, scale the curve to reach the TE and rotate it to perch the tip onto the rectangle line. Doing this for all foils top and bottom is slow.

If I simply take each foil and scale to fit its position on the plan and create the surface, is there a simple way to pick up the trailing edge of one surface and lift it up exactly 0.25mm along its length? And same for bottom, giving a TE gap of 0.5mm all along from the wide centre to the narrow tip?

I had a look at softedit and can do it for the curve, but can’t understand whether it would work for the surface here.

thanks, you guys are awesome - it’s very tempting to ask you for such advice!

Andrew


(Pascal Golay) #8

Hi Andrew- it sounds like, depending on the curve, you could just select the TE control point and move it .25 in the vertical direction from its zero thickness position. This will change the foil shape either a little or a lot, depending on how the points are- Can you post a file with the curves?

-Pascal


#9

If I understand correctly you have one foil profile that you copy, scale and rotate into the correct positions in parallel stations along the wing. I think you should be able to do that all in one go with the Orient command (AKA orient 2 points). You would need to use the copy and scale3d option in Orient.

-jim


#10

This is how I handle wing tips. With blends and sweeps.


#11

Jim, that’s a great tip … I’ll try that for the next one, thanks.

Pascal, some people or software methods elect to open up the foil from its thickest point, so that the change blends from the full 0.25 lift right at the TE, to nothing at the thick point … I worked out I can do this with soft edit curve. But I was wondering if I could do a similar thing with soft edit surface: i.e. quickly build the wing shape without modifying anything, and then “lift” the entire TE by the same amount right across its span. I got the impression that it should be possible with soft edit surface, but I am not sure.

Stratosfear … that looks great. I’ve done them by putting increasingly small foils right to the very tip, but I have struggled to tidy up the very end. Not that it matters too much as I think you can run out to a tiny foil of only a few mm chord at the tip, and just chop it off square … a quick rub with sandpaper when you pop the part out of the mould would be all thats needed.

When I have time I’ll see if I can create and upload a file to try this, perhaps in a different thread.