Loft With Guide Curves - Can More Guides Be Added "Later"?

Hi Folks,

I have a question on a lofted surface construction. If I create a
loft with (or even without) a guide curve and determine that I need to
add another guide curve later, can I do this without deleting the
feature?

I'm not finding anything good in the manual about adding more guides
once the surface feature exists.

Any advice is appreciated. I'm not in a bind, just trying to figure
out if there is a way.

Thanks,

SMA

 

Sean,

Yea, you can. You should not have to delete the loft or start over just
to add or delete a gc of profile.
You should be able to add/delete a GC in the list at anytime.
If there is a problem, it's usually because the GC is not intersection
the profile(s) (although I've seen a loft work even though the GC's are
not intersecting exactly).

Or you can also add more loft profiles by placing your cursor above or
below in the list or moving the arrows on the side of the list bumping
up or down the order of the selected profile.

Generally, adding or deleting GC's is not a problem. And you can
reorder them as well but I do not believe it matters or has it ever
mattered what order they have?

BUT, the loft interface is not without problems... I have often seen a
problem where adding profile will mess up the order of the loft so bad
that you have to start over or remove some of the profiles and change
the start/end condition and exit, they reinstate the profiles. Also,
sometimes when removing profiles or if a profiles start/end direction
(edge of a surface or curve is reversed) the loft interface gets
confused and will not allow for any other profiles accept the ones uses
earlier. In that case, if you run into it, you may have to delete the
loft and start over? (you'll know what this happens, you can not select
anything or it rejects all selections,... one of those consistency
things or the loft feature becomes corrupt?)
Yep, a very strange interface sometimes and I believe it is due to all
the different algorithms which the loft interface has used over the
years. (redefining lofts between releases and sp's is not always
pretty.)

Hmm,.. you're right, I can not find anything in the help with specifies
this?
But you should be able to add/delete at anytime.

 

Paul / Sean

It does matter

Ed gives an surface loft example in Curvy Stuff 201 , slide 36, (see thread
above) showing the difference reordering guide curves can make.
The first guide curve, as I understand it, drives the "flow" direction of
the isoparm lines. If the guide curves are radically different in character,
this can make quite a difference to the outcome.

Wouldn't it be nice if SolidWorks would tell us this stuff in the
documentation, rather than us having to rely on the brainpower of guys like
you and Ed to reverse engineer this information, not to mention the altruism
to then take the trouble and time to share it around? Anyone who's "been
there" knows how much longer it takes to pass knowledge on than it does to
acquire and apply it.

I doubt that SldWks were unaware of the special significance of the #1 guide
curve. I shudder at the waste of effort that is inevitable from their
decision that we, the users, do not "have to worry our pretty little heads"
about stuff like this.
I'm not just thinking of the effort of Ed to infer and document this, but
the waste of effort for guys like us, (well, me anyway) who get perplexed
because of the -at best- inscrutable, and at worst capricious behaviour
software exhibits when it is obeying rules which are kept secret from us.

Interesting question: does this pearl of wisdom appear in the new 1000 page
pdf?

 

Andrew,

For a surface loft by itself, gc order should not change the way the
surface looks?
(Otherwise, I'm not sure what gc order or issues Ed is referring to in
the 201 and 102 ppt?)

But, for downstream referencing, order can be an issue... for
instance,..

http://zxys.com/swparts/gc_order_issues.zip

(this is a touchy subject for me, see note comments)

...

 

Ah, doing a few more test... I think I understand the picking order Ed
is talking about... it's related to cases where the initial "profile"
picking order or how/where you pick the profile makes the gc order
dependent?

But, yeah, I've seen this dependency, and imho, another screw up by SW
Corp, imho.

So, if/when you do see or have a problem with the loft failing,
reordering of the gc's such that they are in the proper "flow" sequence
(like the profiles are) is the remedy.

...

 

Also, to solve the problem, you can "re pick" (clear the list, and pick
from the opposite side, i.e., the end profile first.) your initial
"profiles" so the gc's are not dependent.

Basically, when selecting profiles for your loft, you pick on a end or
location where the initial (or imaginary if a gc is not used) gc would
pass/flow through the sections. If they are open profiles (surfaces),
then you pick near the open ends where the gc would pass/flow.

And similarly, when selecting gc's, you should pick them in order (but
that is because of old habits, which seem to help due to limitations
with SW).

...

 

Paul - Thanks for your advice - I knew that somehow it shoudl be able
to be done.

Here was my original catch 22 - I make two loft sketches and a guide
and form my loft surface. Now I need to add another guide, so I add
another sketch to touch the loft in the right points . . .etc and
shoot . . . I need to edit the feature, which makes the new guide
curve suppressed as it comes later in the tree, so maybe I need to add
something before, but . . . nope . . . it has to relate the loft
sketches, so it can't come before . . . "so he asks"

After reading your message I knew I was not fully insane and went back
with victory in site. What I found is that if I rolled back to the
last guide curve, in the feature, the feature would temporarily
"unabsorb" and let me add another guide (which I had to add manually
to the loft later, but it worked).


It told me:
"You have chosen to rollback to Sketch3 which is absorbed in feature
Surface-Loft2.
The following features will be temporarily unabsorbed for editing
purposes:
Sketch1
Sketch2
Sketch3"

This unabsorbtion was something I had not seen too much, but now it's
crystal clear once I went thru it.

Thanks again-

SMA

 

Ed's example definitely shows a surface loft, with multiple profiles. but
only 2 guide curves. This loft yields quite a different shape, using the
exact same sketches, when you reorder (not repick) the 2 guide curves, using
the "Up/Down" arrows provided alongside the guide curve list for that very
purpose.
There is no sample file provided (Ed's speaker's notes say that it is
included in Curvy Stuff 101 - 2 - Four types of loft, but it's not in the
download I made last year)
I have seen this on my own models, and I'll investigate further when I get a
moment.

 

Andrew,

Well, I had to download Ed's file to understand what you are talking
about,.. the "slide 25" file.
There are actually 3 examples using similar profiles and gc's.

The file first shows the issue of the initial profile chosen and how it
makes the gc order dependent. (in this case the 3 gc's reside between
the ends of two open profiles)
He then shows the same profiles chosen from the other end of the
profiles and the gc's are now not dependent on order.

Only these two cases use the same profiles and gc's "but" the profiles
start/initiate in different order/direction, which changes the way the
face looks. And, for some reason the "Start tangency, All faces of
1.00" is not checked?" Anyhow, they are not exactly the same, but very
similar with face tangency applied.

He also shows that adding a gc at the end(s) of the two profiles
corrects the gc order. (the extra end gc makes it a different loft)

So... the examples are not the same, and it does not show how gc order
changes the look of the face.

see image... http://zxys.com/profilegcs.jpg

This whole exercise (although appreciated) reinforces the problems SW
Corp has with lofts.

... (so much fun)

 

Paul

On further investigation, I found (in the same presentation- (Curvy Stuff
101-2-Four kinds of Loft) a downloadable model with a surface loft in it
which is near enough to the one used for slide 26

Slide22_B - C2 tangent guides better.SLDPRT is the model

Surface-Loft4 is the feature

If you reorder the guide curves and change nothing else, the look of the
face changes in a similar way to that shown on slide 26

 

Andrew,

Well then, sadly, the two files of the "seat back" are showing problems
with lofts in a different way.
In this case, the gc order is changing the way the loft solves and the
surface is not passing through the sections properly.

Files:
slide22_A - C1 tangent guides freaks the model out
slide22_B - C2 tangent guides better

If you open up the file in SW2004 sp2.1 and ctrl-q the loft changes.
If you delete the loft and remodel it, the loft is different looking.

BTW, the illustration on the PPT page 26 has 4 more profiles to correct
some of the problems.

I feel like I'm somehow defending gc order? But, I'm not surprised, I
just have not had many if any problems with gc order. Maybe it is the
way I model or choose my curves... and I thought I experimented enough
with profiles and gc's??? (this is a bad dream)

What this all reaffirms and is telling me are lofts in SW are totally
inconsistent.
And that does not help you or me in explaining or solving some of these
issues.

SW Corp needs to stop wasting our time and solve these inconsistencies.

...

 

The guide curve order thing is subtle and easy to miss - the seat back just
shows a really, really dramatic example anyone can understand. I first ran
into the problem when a part didn't match up to what it was supposed to be,
because of a change of a few thousandths due to guide curve reordering. I
have no idea how many other parts I have done where I didn't notice, or
where the subtle change didn't matter at all.
I have been trained by my experiences to never delete a loft and remake it
(there are always tricks that can be ustilised to save it so the legay
algorithm is used), and to number my guides so I can always tell which is
the first one. It prevents many issues that pop up with service packs. As
a matter of fact, I think SP2.1 is the first that I remember where lofts
that had not been redefined actually changed substantially (instead of the
usual rebuild error where it palin couldn't complete). Of course my
experience is clouded by usually not changing service packs in the middle of
a job.