Shell woes (NX5) 1

[speedster29]

I have a part that was created using various extrudes, curve meshes, and surfaces sewed together. I need to shell it to a thickness of .08", but the operation fails at any thickness greater than .06" with no indication why. I have an almost identical part that will shell at .08" Any advice on how I can troubleshoot my part?

 

[uwam2ie]

1. is your sheetbody oK? -> analysis-> examine geometrie
2. tiny faces anylisis -> minimum radius

 

[speedster29]

It passes all object and body checks. How do I check for minimum radius?

 

[hudson888]

To check for minimum radius you could use the graphical radius analysis tool or simply Analysis>Minimum Radius. The graphical analysis tool generally tells you a lot more, but small radii are not the only reason that some geometry won't shell.

The shell tool has been improved over subsequent previous versions so that if your body is comprised of simple circular blends a great many of the more difficult cases can be handled including but not all that consume underside blends. Look for free form surfaces with tight internal curvature, variable blends that reduce at some point below the shelled size, and importantly corners and steps where flat faces are consumed by the thickness.

If you're stuck then you may ultimately want to try using a series of trims to quarter the body attempting to shell it repeatedly until you're able to isolate the area or areas that are causing it to refuse you. If you're able to discover roughly where the problem is then you may be able to shell to a lesser thickness and by looking at the inside surface pick the site of the problem.

Hope this helps.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[speedster29]

Through trial and error I found that if I removed a surface tangent condition from the mesh of curves the shell was successful. The change in the mesh shape was very subtle but it made a difference to the shell calculations, apparently.

 

[hudson888]

Well I wouldn't want a non tangent surface if I could help it. What you'll probably find is that when tangent the internals of the surface are being forced too tersely into meeting the adjacent face or faces there will either be a tight radius or even and ogee (inflection) just inside the edge of the offending surface.

Sometimes if you have forced tangency to a very tight tolerance the better way is to relax it. Otherwise if the geometry permits then you may throw in an intermediate curve to control the shape of that surface without allowing the radius to reduce so much. Finessing the surface doesn't always come easily but may be necessary to maintain the quality of model that you require.

Lastly if all else fails a too small blended edge in surface is often best left off and patched on after the shell. Since I can't see your model I couldn't advise as to what may be appropriate in your case.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[speedster29]

It's good enough for now because the design is still in a state of flux. When the final shape is decided I will take more care to make sure the tangency is correct. I did add another intermediate cross curve to control the shape.

Regards,
Richard

 

[Drinkin]

I do packaging design of bottles so i deal with this on almost ever sla i make shell doesnt like small stuff.

The best work around i have come up with is to offset surfaces .08 keep adding sufaces till it fails unselect that surface and keep going you will find you will get most of the model. Then just rebuild the mising surfaces sew up and subtract.

some of our shells take longer than the model

 

[speedster29]

Thanks for the tip Drinkin, I'll try it if I continue to have problems.