topic Re: Surface won't offset in AutoCAD Forum

Surface won't offset

Anonymous — Thu, 08 Sep 2016 14:52:24 GMT

I have a fairly complex surface that i tried to offset and it failed so i created a simpler surface and that also failed. It proceeds to the last step and then i get the message offset failed.

Appreciate any help.

Re: Surface won't offset

john.vellek — Thu, 08 Sep 2016 16:22:55 GMT

Hi @Anonymous,

I was able to offset the surface after I used Smooth, Optimized. Will this work for you?

Re: Surface won't offset

Anonymous — Fri, 09 Sep 2016 07:49:18 GMT

John

Thanks for the reply.

As far as i understand to SMOOTH the surface it has to be converted back to a mesh. I did this and presuming OPTIMIZE is REFINE MESH i did that. It then just locked up on converting to a surface. The blue ribbon which appeared bottom left ran about 25% and stalled.

I presume i'm not fully following you.

However, having read more i converted the surface to a NURBS surface and it offset perfectly, i think. See file.

I am new to NURBS and don't really know what i'm doing, but i will.

Is what i've done a useful way or is there a better solution?

I set the original model up from a set of cartesian co-ordinates, created 3d faces and then through to the surface. I understand, from reading, that this may be a historical procedure.

Bob

Re: Surface won't offset

Anonymous — Fri, 09 Sep 2016 08:43:52 GMT

I have been playing around with NURBS and created a matrix of points 4 x 5 with the central six raised by an amount in z. I then splined through these points in the xy plane and used the surface loft tool. I works beautifully and offsets great. The surface is automatically produced as a NURBS surface.

Re: Surface won't offset

john.vellek — Mon, 12 Sep 2016 13:39:16 GMT

Hi @Anonymous,

I am glad the NURBS approach worked well for you!

Re: Surface won't offset

Anonymous — Mon, 12 Sep 2016 16:23:58 GMT

John

Whilst the Nurbs route worked for the simple model i had i was hoping you could have explained in more detail how you got the simpler surface to offset.

I'll articulate the real problem and hope you someone can help. (Should I post it as a separate issue?)

I have a 3-axis CNC machine and wish to make a timing cover for a 1930s motorbike.

I can by various methods get co-ordinates of the surface, as many as necessary, and via these co-ordinates i need to produce a surface which is pretty close to the original. The cover needs machining on both the outside and inside hence i need to effect an offset from the outer surface to produce the inner surface.

Whilst i haven't got the timing cover co-ordinates i created an hypothetical model that in some degree reflects reality.

From these co-ordinates what is the best method for generating the surface?

I have tried splining, network surfaces, 3D Faces and others i can't remember.

The co-ordinate model is attached. The real cover will probably be more Y-shaped which, from my limited knowledge means the network surface method might not work.

Hope you can help.

Bob

Re: Surface won't offset

john.vellek — Mon, 12 Sep 2016 19:21:01 GMT

Hi @Anonymous,

I am guessing this would be better handled in Inventor or Fusion (You might try one of the free trials) but here is what I did in AutoCAD:

I used 3DPOLY to connect each set of points

I used LOFT and selected each 3DPOLY in succession to create a surface

Lastly, I used SURFOFFSET to offset inward.

Please select the Accept as Solution button if my post solves your issue or answers your question.