Master Model Part 3: Sketch Blocks

Ok, let’s get back to the master model discussion.

Blocks sound very Autocaddish, but trust me, they are part of my new workflow with master model when using a sketch to design a mechanism. Or they will be, that is, after SolidWorks works out some kinks. I feel like I have to make a case for this. I expect people who have rejected an Autocad lifestyle to also reject blocks. But they really do make sense for use in SolidWorks model sketches, in addition to the more traditional uses in drawings.

I use sketch blocks in model sketches to create a set of sketch lines that move together as a group without making a bunch of crazy relations and dimensions. You can link together blocks to make mechanisms made out of shapes.

Here’s an example of how blocks fit into the master model discussion:

Model of vice grips. Each part of the assembly is represented by a block in the orange sketch. Blocks are easy to create, just select a bunch of related sketch entities, right click and select Make Block. I even have a hot key for that – Ctrl-B.

You can’t do everything with blocks, for example distance mates are difficult, as are a few of the other advanced and mechanical mates, but you can simulate most of the mechanism in this way without being as literal as building a solid model. Many mechanisms are just 2D motion, and can be handled easily in a 2D sketch with blocks.

With the dump truck, the bed and lifting mechanism is a great candidate for a sketch block. It’s just like cutting out little sheets of paper and putting them together in various ways to do something like arrange furniture in a layout of your house or office.

You can still use blocks in most of the ways that you can use regular sketch entities. You can edit or explode them, and there is something you can do with blocks in a sketch that you can’t do with parts in an assembly: select a single point and anchor it. This drives me nuts in assemblies. If you want a part to pivot around a point, but you don’t have anything to lock that pivot point to, you are kind of stuck. I wish you could pick an edge or a face or a point and say “fix this” rather than fixing the entire part. Anyway, with a block, just click on a point, and click the anchor, and you can pivot about that point.  You can scale and flip blocks as well. All of this make blocks a great tool for conceptual modeling.

Now I realize that master model is often thought of as a technique to drive a finished parametric model, but I also use the technique to quickly make a concept assembly from a multibody part. Blocks may or may not have a place in a finished model, that’s really up to each organization to establish in best practice, but I’m just saying there are several useful techniques you can use blocks for.

But there are some problems with blocks. I had one that when I changed dimensions of the part it was dimensioned to, the block would spin 180 deg. When you place a block, you had better have it oriented correctly, because you can’t flip it. In order to flip it, you have to add a sketch line to the sketch that the block is in, and then use the Modify Sketch tool to flip the block. There may be other ways of doing it, but that’s how I do it. The Modify Sketch tool is grayed out until you add another sketch element to the sketch with the block. This is a bizarre limitation. Blocks in general are always grayed out even when they are in the currently active sketch.

This second problem could have several solutions. One would solve a lot of other problems in SolidWorks, that being the ability to flip entities on planes, plane normals, and that sort of thing. With SolidWorks dumbing down the software for “dumb as a lightswitch” users, and focusing on anything but geometry right now, I’m not sure we’ll see tools like this maybe ever.

Another problem with blocks involves colors. You cannot change the color of a block, even though you can change the color of sketches, and individual sketch entities. To get the picture of the vice grips, I used the dynamic highlight color and just hovered the cursor over the sketch in the feature tree.

The final problem with blocks that I want to talk about is that blocks don’t work in 3D sketches (unless you are sketching on planes in 3D sketches). The “Layout” functionality SolidWorks added is essentially a 3D sketch. So the intended major layout tool does not allow sketch blocks, except in certain situations.

Anyway, blocks in model sketches have a lot of limitations, but they also have a lot of strength. I like to develop techniques around tools with useful functionality. So I use several but not all of the uses of blocks in model sketches.