Never underestimate the power of a midget

Coach Mark, who trained my son during last year’s baseball season, was proud to lead a great team of “midgets”.  He led them from mere midgets, all the way to becoming last year’s champions of their own division. Most of the kids in the team, including my own gentle giant of a son, were not as big or tough as many kids in the rival teams. Some were scared of being hit (yet again) by the ball. But, whenever in doubt, Coach Mark would always say to them: “Never underestimate the power of a midget”.  And he was right! Midgets can grow, and they often do, in amazing and unexpected ways. They can also become stronger, resourceful, skillful, and develop character, often as a result of being treated like a midget.  That’s a good thing for the midget (guess who’s already making the MVP list this year), but not so good for those that never saw it coming and certainly would’ve never expected it from a “midget”, like that coach of the rival team that lost the championship to Coach Mark’s bunch of midgets.  It is also not a good thing if the midget in question happens to be a small error in any of the features in your model. It may be an insignificant error, but one  that has the power to cause most or all of the features in your model to fail.

The following example is something that actually happened to me while preparing for the CSWA test. I was working on the exercises in Planchard’s guide that required changes to be made to models that had been previously created.  Just for extra-practice, I decided to edit this particular one that you see in the picture, and change a few of its dimensions.

I made a mistake, however, and added a tiny extra line to one of the sketches. The line was on top of another one, and was so small that I didn’t even notice it. Well, guess what happened to my model. This happened.

One small mistake and now 90% of the features in my part fail! What do you do when something like this happens? Do you…

a)    Tap your heels three times and reload, wishing that the errors will be magically gone?

b)    Proceed, from the bottom of the tree up, deleting dangling relations and dimensions left and right, in hopes that it would all be better once they’re gone?

c)    Make use of the different editing tools that SW offers in order to find information and repair the model?

Well, if you know exactly what you did that may have caused the problem, just go and undo it, but if you have no clue, then letter c is your best bet. Now, how do you find out what’s wrong with the model? Well, the way SW will handle the errors when they occur, depends on your choice of settings. If you go to Tools, Options, System Options, General, you will find that you can check the option “Show errors every rebuild”.  This ensures that an error dialog box appears after every rebuild, showing a list of everything that is wrong in the model, including errors, that prevent features from even being created, and warnings, that don’t prevent them from being created, but will still show problems, usually with dangling relations and dimensions. You can also display the “What’s wrong?” list of errors if you right-click the name of the part in the feature manager and select “What’s wrong?” from the menu. The list you will get looks more or less like this for a part (it can look much worse than this).

And can look like this (or worse) for an assembly.

OK, so now we have a list of errors, what do we do next? Well, we start editing and repairing the model from the top, from the very first feature that shows an error or warning, and go working our way down. It could be that solving just one or two errors that were made early in the process will solve all the problems in the part. OK, this doesn’t always happen this way, depending on the complexity of the part, but it could. Remember to always hope for the best, even when you are expecting the worst.

In my case, at least, it happened that way, because the mistake I made was located precisely in the base sketch. This extra line in the geometry was causing the base feature, Extrude 1, to fail, and creating all sorts of problems all throughout the model, since all the other entities that depended on that first feature were now failing too and/or had dangling relations and dimensions, now that part of the geometry was missing. When I edited the base sketch, and with the aid of the Check Sketch for Feature command, I was able to pinpoint the culprit. The extra line in the geometry is highlighted in green and now I could simply delete it, rebuild my model, and proceed to repair the next error(s), if any. In my case, there were no more errors and my part was finally able to rebuild correctly.

There are many other midgets that can be causing the features in your model to fail. Some will be easier to spot, like if you made a typo and wrote a value for a fillet that is way too large. Some may not be that easy to spot, but can also be repaired, like if you established relations or dimensions that reference to things that no longer exist in your model. For this situation, you can use Display/Delete Relations while editing the sketch, in order to find the entities that are used by those dangling relations or dimensions and, if possible, replace them according to your design intent, so the model makes sense again.

From this experience I learned that it’s always worth trying to repair a model first, instead of going on a deleting frenzy, which may actually make the problem even worse. Of course, how long it takes to do such repairs depends on how complex the model is. I know many of us will probably have to spend several hours repairing something that someone else (or even ourselves while trying to do changes to it) messed up, and I’m sure it won’t be fun. Sometimes it may be easier to start from scratch? Then again, if it’s still possible, I guess it’s worth trying to repair.

Oh, just to share. Here’s a picture of Coach Mark and his happy bunch of midgets.