In the previous part I explained how I created a very simple solid model in PowerSHAPE 2010. In this part I will try and edit that model. While I was modeling, PowerSHAPE kept adding items to what seemed to look like a feature tree.
The first thing that comes to mind when looking at a feature tree is how to edit the parameters of the features in the tree. Double clicking on an item in the tree window pops up a dialog box to edit the parameters of the feature. I wanted to increase the height of the base block from 0.5 to 0.6. So I double clicked on the item titled “Base” and got this window.
I edited the Length parameter and the height of the base block increased (highlighted in blue in the image below).
Notice that the pins were not pushed up and stayed where they were. In a history based parametric feature modeling system, the pins would have moved up because they are tied to the top face of the base block. But that didn’t happen here. Quite interesting.
OK. So what if I wanted the pins to move up as well? As it turns out, I need to edit the Length parameters of each of the extrusions features of the pins. And no, I cannot simply change one length parameter and expect all the pins to get extruded. Although the pins were created as a pattern, the pattern feature is nowhere to be found in the tree window. Which means that the eight pins are on their own. So I double clicked on each of the pin items in the tree window and changed their length parameters from 0.2 to 0.4.
After changing all eight Length parameters, I ended up with the following changed model.
But wait a minute. Is the last hollow operation still intact? I used dynamic section to find out.
Looks like PowerSHAPE updated the model to maintain the features that were added downstream. From the looks of it, PowerSHAPE appears to be a lot like a history based parametric modeling system. Well, not quite.
If you remember, when I increased the height of the base block the pins stayed put. So it appears that the pins are not linked to the top face of the block. If that is the case then I wonder what will happen if I decrease the height of the base block instead of increasing it. That would leave the pins floating in space, wouldn’t it? One way to find out. I decreased the height of the base block to 0.4.
I got this error message.
The height of the base block was reduced but all the pins disappeared.
The tree window had a devastated look on it.
The only two features that could be defined were the first base block extrusion and the last hollow feature. Rest all failed. So from what I can deduce from this little experiment, PowerSHAPE maintains a list of features and the order in which there were created. However, features are not completely dependent on each other. That’s why the pins didn’t move along with the top face of the base block. Features will build or fail depending upon whether the features before them are able to give them adequate support or not. For example, the pins are defined by cylinders. When the height of the base block was increased the cylinders interfered with the block, which was good enough to do a boolean union. However when the height was decreased the cylinders were left dangling in space and could not be accommodated anywhere in the base block. This can be see from the error message that pops up when trying to edit one of the failed pins.
The interesting thing is that the final hollow feature wasn’t really bothered with the pins at all. So when PowerSHAPE finally tried to apply the last hollow feature to the blase block, it got applied without a problem. This behavior is quite similar to how you can suppress features in history based parametric modeling systems.
In the next part I hope to dig a little deeper into what Delcam calls Tribrid Modeling, which is the sum of solid, surface and mesh modeling. In the meanwhile you can check out this video.