edge/face blend woes 2

[WRMorrison]

NX10

Can anyone help spot what I'm doing wrong here? I'm trying to add a "simple" .5R fillet to the inside corner shown. I've tried both edge and face blends, but I'm no expert with either. It's always that last little bit that it won't apply the blend to. Ideally, the picture shown with the attempted face blend is what I'd like to achieve (or similar), but it would have to "patch" the missing surface (shown by the green/yellow adjacent surfaces).

Any ideas?

-WRM

 

[Toost]

I don't think that you do anything wrong at all.
I think You have encountered an geometrical situation which is very difficult to handle for a blend.
Quite often the difficult thing for a blend is how to start and end, not the tangency conditions.
The red highlight is the edge of a face which seems to bend in-over the new blend, there is the problem. The blend has difficulties stopping/ trimming at/to this face.

Try make the new blend slightly smaller such that it's tangent line don't touch that face, i guess that it will work.
Try see if you can temporarily delete this small face and if the blend then works.



Regards,
Tomas

 

[Felix K. Holloway]

Toost has outlined the most likely scenario above. Also, if you are not absolutely required to maintain a 0.5" radius in this blend, you can make your blend "variable" within the same edge blend function.

Under the "Variable Radius Points" rollout menu you can select multiple points along your curve string that will each have a different radius value.

You may be able to have 0.5R all the way till very close the the end then tapering down slightly to where the blend works, maybe 0.45R or something.

Play around with it and see what works. Like Toost said, you have encountered a geometry set that is not calculable with realistic 3D results, nothing wrong you yourself are doing except maybe planning your model out to avoid such conditions.

You can also get creative in these situations if you are completely cornered, by making your own wireframe and custom surfaces/solids in these types of regions. I would not recommend that as it not really good practice but it can work in a pinch.

Felix K. Holloway - Designer - NX 9 & 11

 

[WRMorrison]

Thanks for the replies; I appreciate it.

I need to maintain the .5R because that is what this feature will be machined with (Ø1.0 ball e.m.). I'll have to try another work-around to get the desired result I guess instead of edge/face blend.

-WRM

 

[Felix K. Holloway]

A trick I use sometimes is to create a face blend, but under the "Trim" Rollout, uncheck the "Trim Body to Blend" option and then make your face blend.

It will be a separate face not connected to your body.

If your main body is a solid, you can now "Thicken" that face, "untrim" relating faces (from your main body) and "Trim Body" of the thicken with those faces, then "Unite" your thickened blend into the main solid.

If your main body is a sheet, you can use a similar process but use "Trim and Extend" on your sheets rather than "Trim Body" and "Unite".

That would be a last case resort though but usually works for me. Better to have clean geometry that works properly but you gotta do what you gotta do.


Felix K. Holloway - Designer - NX 9 & 11

 

[LynnB1]

Could you reorder your modeling steps so that the blend is applied first, before that corner is shaped/rounded off?

 

[John2025]

I feel your pain, we have the same issues fairly often on complex shapes like that. Sometimes we just leave off the radius and let the ball mill cut the radius. It's a little annoying that the machining software can calculate where a ball mill needs to go, but not be able to deal with it in modeling. Oh well, nothing's perfect.
John

 

[Felix K. Holloway]

The machining software is just following a path, and doesn't have to reconnect faces to make things work. I often hear people upset that CAD software cannot perform miracles and "Just make it work"... If CAD software was that smart, we'd all be out of a job... Let's face it, CAD is A LOT easier these days then it was before... My boss constantly reminds me that in CATIA V4 you had to make every fillet "by-hand" essentially...

Felix K. Holloway - Designer - NX 9 & 11

 

[John2025]

Yes, it just has to follow the path, but it seems like if you can calculate the 3D offsets required to maintain that path and know the radius then you should be able to recreate the face. I agree CAD has improved greatly, I had to write loops in G code that calculated the new x,y,z,i,j,k points at each loop in the old days, but I still retain the God given right to bitch and moan when the software's not perfect.

 

[Felix K. Holloway]

Amen to that brotha!

Felix K. Holloway - Designer - NX 9 & 11