Is trimming of native solids ok?

Hi,
V5
There is theory and actual experience, hearing from those who haven been there done it got the t shirt !
I am hearing that trimming should be kept to a minimum on surfaces,

( is it also by the way better to trim then dupedge that trimmed edge and remake the surface with that as rail etc ? )

My big question…am I ok to trim native solids or should I be creating cutting solids and using booleans ?

I just dont want trims to come back later and cause problems. I cannot afford to find out the hard way on this job.

Rather than trim blocks I am using scale 1d to shorten them !

Steve

First, you should keep in mind that there is no bad tool in Rhino. (I was tempted to shout here)

If you trim with an object that is less than optimal, be it a curve, a surface, a polysurface, you’ll probably get bad results. The inverse is also true.

I would see no benefit to doing this. The reason that some people don’t like trimmed surfaces is because the trimmed edge is heavy (lots of points). So if you try and use it for an input rail, one side of a loft, an edge to match to, etc. the resulting surface will be heavy as well to match the trimmed edge. So if you duped your trimmed edge, then tried to remake you surface using that trimmed edge, you are probably going to end up with a heavy surface. A trimmed light surface will most likely be more usable than an untrimmed heavy surface. If you can replace the trimmed surface with a nice clean untrimmed one, then great. If not, it is not always the end of the world.

Booleans are really just trim and join macros. So it doesn’t matter if you do the trimming and joining yourself, or you use a Boolean command to help you out.

I think you have gotten a little gun shy on this trimming thing without knowing why you’re shy of trimming. In the quote above, I assume by blocks you mean cube like objects, which usually have planar sides. Unless you are cutting with a really heavy curve, the resulting trim will be as light as the curve you used to trim, so there isn’t too much to worry about there.

1 Like

Hi,
Gun shy…nice term :smile: I guess so, just trying to not fall into potholes having had trim bite back and having been told it was to blame, I used to think one could surface then trim at leisure. Then I found a few days ago that joining surfaces together failed as they were trimmed. MatchSrf requiring untrimmed edges.

Its all a case of knowing the dos and donts, wills and wonts !

its not always possibe to think ahead and see that in a few months time that edge after its been copied into another file then this or that is done, will need MatchSrf.

I can now go trimming my cube like objects with straight lines with impunity. I know their planned existence.

Steve

That doesn’t make sense, Steve. Surfaces do not join because the edges are not within tolerance; not because they happen to be trimmed.

Trimmed surfaces are safe, BUT avoid trims that ends up being tangent to edges as it can cause trouble. In those scenarios it is better to extend the surface before trimming so you have a “pure trim”.
Rhino also has trouble sometimes with boolean operations where the surfaces are coplanar, so instead extend the solids so they have enough overlapping volumes.

Hi,
Hi,

wim
That doesn’t make sense, Steve. Surfaces do not join because the edges
are not within tolerance; not because they happen to be trimmed.

MatchSrf command says :-
1:Select an untrimmed surface edge.

It simply wouldnt select my edge, when I went back through what I had done and ditched the stage when I trimmed it, then it worked, though it caused a gaping hole.
see:-
thread Simple shape for sweep2 as advised but why both options results bad?

(I did clean up the curves, it still refused)

Holo
Trimmed surfaces are safe, BUT avoid trims that ends up being tangent to
edges as it can cause trouble. In those scenarios it is better to
extend the surface before trimming so you have a “pure trim”.

any chance of what u mean as a visual screen dump etc ?

Rhino also has trouble sometimes with boolean operations where the
surfaces are coplanar, so instead extend the solids so they have enough
overlapping volumes.

I noticed that, there are times I have one solid touching another as part of its shape and boolean fails as it seems not to know if it is or isnt intersecting with the other solid. I hate those times !
Steve

Steve, Match Surface is a very special type of joining, whereby the curvature etc. of 2 surfaces can be matched. That doesn’t mean that no trimmed surfaces can be joined - they can as long as their edges are within tolerance.
But only untrimmed surfaces can be matched.

Hi Nick,
Joining and Matching. I need to fully understand this.
MatchSrf by the very name matches surfaces.

so they need to be untrimmed.

I created two planar straight 4 sided surfaces making them meet at one corner and small gap at the other and used MatchSrf. it actually curved the one shape until I found a combination of settings that saw it go straight. There is no preview option yet it updated but then deliberately going back to the first choice after finding the non distort set it didnt distort.

I saw no join option throughout both in command line area or in panel. clicking Ok the surfaces were still unjoined though matched.

The join you refer to, is that within the command ?
MatchSrf test.3dm (43.3 KB)
Steve

Joining surfaces together is done with the Join command.
I think you don’t see MatchSrf as it is, well constructed surfaces should join without doing a MatchSrf first, except in some situations like when the construction method doesn’t allow continuity on all the four surface edges.

Hi, yes I use join, this task and query was created following Pascals use of Loft on profiles that shared the same rail, saying use matchSrf where a thin gap exists, when I tried matchSrf it wouldnt run as I had trimmed the sharp corner off the loft first. and when I did the matchSrf first it created a gaping hole.

see here for this.

and my storyboard of images partway down.

i have refined the curves since by the way, it still does it !

Steve