Although this thread has turned into strange complaints about many things, there's been very little response about the original post. I've just had a quick look at the scenario as laid out by propstuff. As a user and trainer, my overall opinion is this example could be demonstrated without failures and embarassment. Based on the original post, my view is that the embarassing failures described are a combination of drawing method choices and the unfortunate choice of legacy tools that are leftovers from the old days.
Here are some of the ways I might have done this differently.
>>The other day I sat in front of a class of design students intending to demonstrate using the various Split, Trim, Combine options. Instead, through an increasingly unpleasant 20 minutes, I managed to demonstrate how flakey and unreliable these tools are in VW.
>>A 4 week old Lab of brand new Dells running XP with VW11.1 freshly installed
>>2D resolution set to Very High, Snap radius 1 Pixel.
Snap radius of 1 pixel might be the first potential problem area, especially for new users. It often seems paradoxical to them, as they think that a smaller radius will make them more accurate. In truth, it is more likely that a small radius will make them miss their snaps, as they have to be right on top of the point or they don't get it. It's possible that this setting contributes to some of the problems described later in your description. It is, of course, a personal preference, but we find that the default setting of 5 is a good balance between ease of use and control.
Another possible factor is the Grid constraint. I can imagine a circumstance where having your snap radius at 1 and your Grid snap on could cause you to snap to the grid when you meant to snap to a point. With a larger snap radius, this won't happen, since object snaps take precedence over grid snaps.
>>Demonstrating the Trim tool on the small sector of circle between the tangents reliably deleted ALL the circle insead of trimming it to the tangents. The lines were not snapped to the circle DESPITE having been originated FROM it.
>>I explain that despite the intended function, no software is perfect, and that the updated version has improved the trim tool.
>>On many subsequent tries of the same task, on different systems with different versions including VW11.5, the trim tool fails about 40% of the time.
I would not use this tool in doing this demonstration. The message that we deliver in basic VW training is that the Trim Tool is an older tool still available because some long-time users will complain if it's taken out, but that is not one to be considered for most tasks. It's functions have been largely supplanted by the Split Tool, which is far more robust and has better functions. See below for how to use in this context.
>>Using the Split tool to split the circle between the the tangents I explain that we should be able to trim each end of the resulting Arc back to the tangents. The Split tool repeatedly just fails to split the circle.
>>I offer the doubtful looking students the explanation that "it usually works". I'm feeling a bit stupid.
On many subsequent tries of the same task on different systems with different versions including VW11.5 the split tool not only fails about 10% of the time, but sometimes actually RESIZED THE RESULTING ARC to, variously, 245, 248, 239.3, etc. On one subsequent retest I discover that the circle that was made by tabbing in 250 was actually 250.02(!?)
>>Eventually I give up and use the Split by line option.
The Split by Line mode is the right way to go in the first place. Split by Point on a circle simply converts it to a 360? arc. This is logical and predictable, but not what I presume you want to do. I have tried but was unable to replicate your failure with this. It could be related to snapping, and a snap on the line or grid instead of the circle when doing the split.
>>I now show them the Combine/Connect tool and explain that it can be used to trim, combine, connect etc.
>>In the third mode I start at the arc on one side and drag to the adjacent tangent.
>>Try again starting at the tangent and this time it works.
>>Students want to know why it didn't work the first time. I offer weakly that some functions need to be done in a particular order. They have "well how are we supposed to know which?" looks on their faces.
This is how the tool is supposed to work. Tell your students that the way that they can tell which order to do it is to look at the two pieces of geometry you are connecting. If the arc is extended it will continue to curve away from the line, making a combining of them impossible. The line extended will connect to the end of the arc, making a successful combination. I use an example just like yours in our introductory course, and by explaining this logic, everyone gets it, sees it as a feature not a bug, and can avoid problems with this tool in the future.
>>Now the other side. almost NO combination of options will succesfully join the remaining tangent to the curve of the polyline. About 5% success rate there, and no repeatability.
I can make this work on our office computers, so I don't know what happened differently for you, but I think it's the wrong method here, because as soon as I do the first combine of line and arc, a polyline is created that already has that final side. It's just not displaying the line. Give yours a fill colour and you'll see what I mean. All that's required is to show that edge using the Reshape Tool.
>>I explain that, as we ultimately want a surface, we can use the surface commands to get the desired outcome.
>>Selecting the Circle and the tangents, I remind them that the Combine into Surface command will use boundary objects to make a new surface. OK, I use that inside the margin of the tangents and circle and make a new "sector" surface, then, I say, that can be added to the original circle with the Add Surface command.
>>Intsead of adding properly, there is a sliver on only one HALF of what was the margin between the circle and the "sector" surface where the surfaces have not met. The students are now either laughing openly or muttering about what crap this is.
>>I undo back to the original circle and tangents, move the objects and zoom a little to centre them on the screen, remake the sector, and re add it to the circle. >>>>THIS time it works and I have a polyline.
>>"What did you do"? they ask, "why did it work the second time" and not the first?.....................................................
>>I don't know.
I think this is another part of your "perfect storm". Combine into Surface falls into the same category as the Trim Tool. I tell new users in our courses that it's a 'legacy' tool only, and its functions have been supplanted with the Compose command, which will do this job perfectly (provided, of course, that the geometry is properly snapped). In re-creating your example, Compose works great.
>>Why would repeating the same sequence of construction and use of tools and commands work sometimes and not others?
>>I have subsequently tested this task repeatedly on 6 different combinations of machines, operating systems, and versions of VW including11.5 to try to offer my students an explanation, and the only thing that was repeatable was that sometimes it worked and sometimes it didn't.
>>The split tool failing to split the circle, the tangent snap failing to snap to the circle, the combine connect sometimes joining the tangent to the arc, the erratic surface commands; in this task were all unreliable AT BEST.
>>It's not as if this was a big ask; joining a pair of tangents to an arc is nearly as basic as geometry gets.
>>Why is VW such a flakey piece of software? Or am I misguided; is all CAD software this unreliable?
>>What am I supposed to tell the students?
I have been in your shoes. When things fail during a live demo, it is uncomfortable, and it sounds like you had a particularly rough class that day.
However, although I have often had problem situations shown to me like the one you've described, they are almost always traceable to some problem with method or understanding of the software. I don't know precisely how you drew this thing, but I think you could have done some things here with different methods. Here there is an added component of the problem, legacy tools that in my view should no longer be in the program. Nothing in the manual will tell you which tools to stay away from, but as one instructor to the other, I think that this is the insight we have to add in order to make our courses more worthwhile than simply reading the manual. My experience is that most users are OK with the information that some tools should be avoided in some circumstances, as long as they know it, and don't have to have the frustrating experience you've related.
You close your remarks with "What am I supposed to tell the students?" Well, this is a very manageable drawing problem. If I were in your position, I'd make this example work perfectly, go back and say, "This thing didn't work at all last time. I'm going to go through this again, showing you a much better method."
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