In this series we’ve been looking into the 3D modeling capabilities offered by DraftSight Premium, Enterprise Plus, and Mechanical. In Part 1 we moved out of the 2D world of the XY plane and started working with the Z-axis. We also looked at different ways to display models on screen. In Part 2, we looked at commands for creating basic geometric shapes like boxes and cylinders and for extruding existing 2D profiles into 3D solids. Today, we’re looking at ways to use 3D bodies to modify each other by adding or taking away volume. Or, in other words, Boolean modeling techniques.
For more information about parametric vs non-parametric Boolean modeling, check out the blog Can You 3D Model in DraftSight?
For information about navigating 3D space and changing view settings in DraftSight, refer to DraftSight 3D Modeling Part 1: Views and 3D Navigation.
For information about creating basic solid bodies in DraftSight, refer to DraftSight 3D Modeling Part 2 – Creating Solid Bodies.
To illustrate modeling in DraftSight, we will walk through the creation of the Model Mania Challenge from 2010. In case you haven’t heard of it, Model Mania is an annual contest held at 3DEXPERIENCE World, formerly known as SOLIDWORKS World. The contest first started over 20 years ago. It pits SOLIDWORKS power users against each other in a test of modeling accuracy and speed.
This part will require the creation of several solid bodies, and the use of Boolean operations to bring it all together. We’ll create bodies representing the front and top profiles, and merge them to make the part’s overall shape. We can add the cutouts to the model by extruding those profiles, then subtracting them from the main body. In the final step we’ll add the fillets.
Creating The Basic Shapes
I could draw each 2D profile in a different area in model space and extrude them, creating a scattered set of 3D entities. Then I could use commands like MOVE and ROTATE3D to position them where I need them before using Boolean commands to merge them into a single body. Another approach is to do all the 2D work first, drawing all profiles where they need to be before extruding them into 3D solids. That’s the approach I usually prefer.
Since DraftSight defaults to the Top view (the XY plane) when creating a new drawing, I’m going to start by drawing the Top view’s outer profile. Going forward I’ll be putting entities on different colored layers just to make things visually easier on us humans. It doesn’t matter to DraftSight what layers we use.
The Front view needs to be rotated 90° from the Top view. So, I’m going to change to a ‘SW Isometric’ view, and then use the CCS command to rotate the X-axis 90°. We can draw a 2D profile in the new XY orientation.
Now we can use either the EXTRUDE or PUSHPULL commands to create solid entities from these two profiles. I used PUSHPULL. The extrusion height given to each body is not important at this stage, so long as they extend past each other. You can use the MOVE command to center them. It’s easy to move a 3D entity from the endpoint to the midpoint of an edge.
TIP: If you find you haven’t extruded a profile far enough, you don’t have to use the UNDO command and then extrude it again if you don’t want to. You can also use the COPY command to create copies of the entity where you need extra volume. In the case shown above I could have extruded the profiles half the length I did. Then, instead of centering them with the MOVE command, I’d have created copies of them on the opposite sides to cover the same total volume resulting in four bodies instead of two. Either way is fine, so long as the bodies intersect where we want them to.
Using Boolean Commands
Now that we have bodies representing the Top and Front profiles, it’s time to merge them together with one of the three Boolean commands, UNION, SUBTRACT, and INTERSECT. If we used UNION, the bodies would be added together to form a single body made up of all the volume of the originals. That’s not what we want here. If we used SUBTRACT, we could remove the volume of one body from the volume of the other. That’s not what we want either.
We want to use the INTERSECT command to create a single body preserving only the volume the original bodies shared. Notice the original 2D profiles are still there. They were not consumed when the 3D entities were extruded.
TIP: In some cases, some faces of a 3D entity will be colored differently than the entity’s assigned color after a Boolean operation, as they can inherit the color of the body which created them. An easy way to fix that is change the entity’s color to any other color, then back to the color you want. All the faces will be reset to the new color. It’s usually a good idea to use the color setting ‘ByLayer’ so the entity inherits the color of the layer it’s on.
Preparing the Cutouts
I could have drawn the 2D profiles for the cutouts at the same time as the Top profile. For clarity in the above steps, I saved them for later. Now I’m going to freeze or hide everything but the top profile, and switch the CCS back to the default ‘World.’ Then I’ll create the 2D cutout profiles.
Now I’ll extrude all three of the cutout profiles. If I use the PUSHPULL command, the lines and arcs of each profile do not need to be joined into a single entity first. But I’d have to create each new body one at a time.
I can extrude all three profiles at once with the EXTRUDE command, but each profile must be a single entity to create a solid body. Therefore, the individual arcs and lines of the left and center profiles would need to be joined together. They can be turned into polylines with the WELD command, or a 2-dimensional surface with the REGION command.
Next, I’ll center the three new bodies using the MOVE command, and freeze or hide the layers containing 2D profiles. Now we’re ready to cut the main body using the SUBTRACT command.
The only thing left to do at this point is to add fillets using the FILLETEDGES command. First set the radius using the ‘Radius’ option. Edge selection is made much easier by use of the ‘Chain’, ‘Face’, and ‘Loop’ options.
There are many who believe DraftSight is only a 2D application. We’ve busted that myth. While it’s true that DraftSight is primarily designed and used for 2D drafting and design, it’s also a capable modeler. The 3D tools we’ve looked at so far are only the basics. There’s plenty more to explore.
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