What command to weld not glue sweep surfaces before OffsetSrf wrecks them?

Rhino Rhino for Windows
1

Hi
V5
Is there a command that will fuse (weld not glue !!!) all surfaces together after the sweep2 phase of a build on an object to stop OffsetSrf creating havoc ?

I had an item made from 9 sweep2 and two surface from 3 curves commands, symmetrical about its centre line.
Thus all edges between surfaces abutt. I had T seams where surfaces at sides met one running around the items open front.
Looked really good, did Join (deliberately avoided JoinEdge being told it will come back to haunt me) and had to solve one naked edge with MatchSrf.

OffsetSrf 2mm and the result gained several naked edges. One staggered T seam, one 1mm crevasse.

Join seems to enable OffsetSrf to mess around. Why cant it simply resize surfaces not create new seams and surfaces. On one rail it had invented a new surface sticking out by 1mm perp to my surfaces the entire length of the rail, yet that surface was swept exactly the same as one on the other side and that one was ok and had received the exact same reshaping inwards of OffsetSrf.

I would like to weld the surfaces together, not glue them ! then use OffsetSrf.

What is best way to do this for sweep surfaces sharing rails thus surfaces abutt to stop perfectly good joints being messed up ?

Steve

2

Hi Steve, this most likely has to do with tolerances and surface continuity. T-joints are also troublesome for Rhinos offset to solve. But the best advice is to share the model so we can give you better advice.

I would also need to know:
What is the part, how big is it, and what are you going to use the model for? At what scale/size?

3

Hi,
The item I wish I could share, but its sort of confidential.
I have sliced two parts off , so can get away with showing that !

I have leader arrowed one area where there is a thin black fold or something going on, I see these yet cant select them The original I feel is fine, maybe it isnt but its just sweeps. I am not supposed to input more time than is enough to get a shape that will mill from, not to go to ultra perfection, and it will have fibreglass laid over it !

size as shown, only extracts supplied, gets made into a solid block and milled from mdf, or foam. as a positive for f/glass coverage.
When it looks smooth and fine and no naked edges its good enough to go. I then have to offsetSrf it then what was good isnt, so then repair it, just when I thought job done, after burning many midnight oils, another sleepless night fixing the offset !, I even cut holes out of troublesome areas and surface patch them. good enough !

I will be doing levels 1 and 2 training etc but meanwhile I need to get this many phases job done first. What I produce gets milled etc so seems good enough, after I repair the offsets.

If I could weld not glue those seams then I wouldnt have offset damage my work !

I get these slivers within the offset result and wonder then how to fix them. I dont want to have to go resweeping parts after offset done. I did try removing this three sides surface and using the surface from 3 or 4 curves command but it wasnt good, yet I am sure I used that to create the original !

The 1mm crevasse occured with my sample portion for you so I am able to show that, so again its not perfect over there but I had to sweep the edge one way 'cos of curved profile then the sides were swept another way dictated by the profiles and rails that were required.

At the tip of the crevasse is by T seam now a Z seam !

OffsetSrf_Imperfections.3dm (1.2 MB)

Steve

4

Hi Steve,
Why do you need an offset if you are going to mill it? In most scenarios you’ll only need the top surface.

In one the first object (the mirrored one) you can replace the middle surfaces with a patch and that will offset. A patch is not super accurate, but neither is the rest of the model, so it should do the trick.

On the other part you have a long “fillet” that doesn’t have tangency to the other surface, and it has T-junctions++ so it needs to be remodeled. I can help you with it, but remodeling others surfaces can cause tolerance issues to the surrounding surfaces, so I would need to see more of the model.

5

Ok, here are the surfaces quickly tuned so they can be offset. They were messy but you are on your way!
For the future try to keep the joints as clean as possible, T-joints will cause trouble with lots of Nurbs commands so try to avoid them if possible.

And remember to return the favor to the next novice on the NG, after you have completed Level 1 and 2. Reading through the PDF’s and doing all the tasks should take you about 6 days of serious studying.

Imperfect surfaces adjusted so they can be ofset.3dm (1.2 MB)

Good luck!

6

Hi Holo and thanks for the 3dm,
Just back from having to do an interim fix to get PC operational again hence the long gap before answering.

The milled shape is to have fibreglass laid over it, f’glass 2mm thick, the result will then be the original shape that I created again.

Thanks for offer of having the full model. If my patched up model causes issues I shall follow up on that. Its confidential so as such strict conditions are attached to it.
The open edge of this had to be swept around the edge, the rest of the surfaces had to be swept from that edge aft, so T junctions were inevitable.

I would have liked to have seen how the extracts were ‘tuned’. When the shape looks fine to me, with perfect sweeps etc, I dont see beyond that to a need for tuning it and as such the offset wrecks it. I do a naked edge search and fix those, then think all is good.
What other commands can I run to show up things that need fixing ? With sweeps sharing rails surely the resulting surfaces shouldnt see oddments form.

Its the fact that the original looks fine, then I have to offset it, then that creates oddments I cant get at that causes me problems.

I hope the training covers this aspect.

some exercises on how to improve a model to stop offset wrecking it would be most welcome, I hope they exist.

Steve