History Hypocrisy

The truth is that most people don’t make models that get much benefit from the History-based modeling scheme. For most parts, no one really cares if the computer remembers that one piece of geometry comes before another piece. Some features are different, like fillets, extruded text, and holes. Fillets need an existing corner to round, and a hole is often located from edges (or are the edges located from the hole?)

This is kind of freaky, because you have a History-based system, but within it, you have features that don’t follow the history thing at all. Like sketches. Sketches don’t know anything about history. Yet you can edit the sketch just fine.

And assemblies, assemblies give mixed signals about history. Mates don’t know anything about order unless you have mated to an assembly feature, then the assembly has to resolve the initial mates, rebuild the assembly features, and then solve the mates made after the assembly feature mate. What’s up with that? Does anyone even understand mate groups and rebuild order in assemblies?

Anyway, the concept of history-based modeling doesn’t push many buttons for people because most of us don’t care. Well, that is, until we do. So what is it that will make you care about history-based modeling? Here, I think CAD users fall into groups:

1. Users who design parts with fewer than 10 features in each part, and pretty simple assemblies.
2. Users who make reasonably simple parts and large assemblies.
3. Users who make very complex parts and any kind of assemblies.

Group 1 really shouldn’t be using history-based software. You should be using something simpler. Honestly. (Geez, is he SAYING that out loud?!?!) Really. Get something that’s not history-based. You’re using like 10% of the software. You should get this free product that one CAD company used to give away called 3D Sync, but they don’t give it away any more. While you’re recovering, I’ll talk to the other two groups.

Group 2 are probably missing out even more. Definitely should be using something meant to handle the type of stuff you do, like Synchronous Technology in Solid Edge. It does both history and direct/Sync Tech, and has some nice large assembly stuff.

Group 3 is making complex surfaced parts, and might have my Surfacing book. These people are pushing the software past where it is intended to go. Complex surfacing doesn’t do well in a history-based method. Ever wonder why all the CGI stuff is done in mesh modelers? It’s because its about 20x faster than sketching splines, making lofts or boundary surfaces, trimming and knitting, etc…

So if it’s overkill for simple parts, and it’s not really meant for complex parts, what is history modeling good at?  The whole history-based system was created by programmers to work with the hardware of 30-40 years ago to solve geometry in smaller, more digestible chunks. Back then, you needed to break it down. These days you don’t need that.

So history-based software starts out-dated, and moves to inappropriate for most of the work that users are applying it to. Why can’t we move on from history? We really need to move on. I’ll keep writing books for history-based software as long as people keep buying it, but I’d rather write books about something else. We get very little benefit from feature order, and we really don’t need to keep solving geometry in small features.

Who is it that actually does benefit from feature order? Just a couple types of features, like text-based extrudes, some fillets/rounds, maybe shell features, possibly some sheet metal stuff? That’s not much to base all of this money we have tied up in history-based CAD, actually. Why have we got this bad habit we just can’t drop? I’m not sure, but I’m going to do my part to get us to move on.

What do we move to? Well, Solid Edge and NX have a good starting place, with both a big improvement on direct editing and the ability to use history-based workflows. Some other CAD packages also can work in the direct edit scheme. I do think these tools are going to need to continue to evolve, as the story these companies have to tell doesn’t seem to resonate with users. But I can tell you, the Synchronous Technology stuff works, and has huge advantages over straight history. Especially for the kind of modeling that most mid-range users do – machine design. For the complex surfacing stuff, move to NX and you’ll get the tools you need for work that currently overwhelms your mid-range modeler.

Can anyone step up and tell me what it is about your history-based tools that make it work better than history-free tools? Really, I want to hear that discussion. What makes history better, more useful? Or is it really that you just don’t know there’s something else out there?