What is best way to recess into the solid outboard from this line?

The attached rhino 3dm file has a solid that is to be milled from solid block mdf. I need to create a ‘moat’ around the black line object, 12mm or more wide and perhaps 5 to 10mm deep (cutter ball is 12mm) or take the entire solid beyond the black line in by say 5mm or more.

How best can I do this ?

Here is an image of the file attached.

I wondered about sweep1rail and use a sphere, if I can get it to remain perp to rail, spheres have no tangible point and orientation to use, or do they ? or maybe a drawn shape.

How would a shape know to remain perp to rail ?..perp to surface in fact ?

A jing video of this would be sure welcome !

Fibreglass matting will be laid over this and the client will need to have some edge indicator so as to trim it to the black line shape afterwards, so a nice fall off at the black line seems sensible !

The lumpy surface by the way is not poor workmanship but deliberate !
Shroud_ForForum.3dm (221.1 KB)

Perhaps offseting the line 1/2 diameter of the sphere might give you the results your seeking. I noticed the curve is in two parts for either side. You could project one curve to the plane, offset it, then extrude it through the surface, intersect and voila, new curve…and just what is this object? Some sort of ankle boot? Sorry for my ignorance. Regards, Rob

If you pipe the curve with the radius of your offset and then intersect that with the surface, that will give you a more or less good offset (one on each side, of course), if the surface isn’t too radically curved. You can also try OffsetCrvOnSrf… But that may be a V5 only command, I don’t remember.


Thanks for the method.
Both are for creating an offset line, the radius of e.g. a sphere or circle if I understand correctly, and I can see how both would work.

OffsetCrvOnSrf I found in V4 and hey presto, I created a 6mm offset line on the surface.

I then opted for the pipe command, a command i wasnt aware of.

It creates a circle naturally perp to the sweep line which you get to place again and again, so I placed them at the tight bends and at other intervals.
I end up with a pipe, which was segmented, so I lessened tolerance to 0.5mm and was able to join them.

Boolean Difference this from the surface, and as usual, it fails.

attached the file as far as this.
Shroud_ForForumPipeCommand.3dm (579.2 KB)

I have searched for naked edges, none show.

If I could boolean this, then job done.

I also tried sweeping the sphere around that 6mm ofset line, but the only command I could see that might create something that way saw nothing happen.

Solid>extrude Surface>along curve

Can one sweep a solid along a curve and create another solid ?

I am working in one part rather than two halves, just incase it works.

Robb. Its an aircraft part.


Steve, your curves for Pipe do not meet cleanly at the lower end - they overlap. If you clean up the curve and make it all one, with no gaps, Pipe should work out better here.

Curve and offset.3dm (70.0 KB)


And since it sounds like you can live with a .5 mm tolerance, rebuilding Pascal’s curve to 400 points (degree 3) and piping that with r=6 will give you a surface that you can successfully boolean from the solid.

spotted that but your post beat me to it, it now works.


…and now I remember I must inset surface 1.5mm to allow for skinning thicknes, so more work !

Hi Steve,

Do you know who is going to mill it?
It might be your curve on the surface is enough information to set the path for the mill.
I’m no miller nor do I have much experience with it, but I suspect the one doing the milling is better off with the curve the mill should follow than the resulting 3D surfaces from which the tool path needs to be reconstruct?

Anyone with milling experience reading this, I’d like to know more about this as I’ve been curious about this for a while.
How conventional is it to provide only milling paths for these type of shutlines/features in a surface?


I ran this past the miller, asking do I need to provide the ‘moat’ as this will be fibreglass matted over and such a depression gives an edge to cut afterwards. He required it. I did ask first incase he could save me messing about !

moat was 12mm dia as he was to use a 12mm dia ball cutter., and he suggested that dia for the ‘moat’