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Part 3: Multi-Body Part Modeling
This series is about driving a Motorcycle in reverse…just kidding. This series is actually a look into what it takes to go from concept to an actual design, and from there to a 3D Printed part. DesignPoint is a licensed SOLIDWORKS reseller and trainer and a trusted partner of Markforged. With these top-of-the-line resources at our fingertips we can turn our design dreams into 3D Printed realities. You can achieve your dreams, too, if you come visit us for SOLIDWORKS training or to learn more about Markforged’s innovative line of 3D Printers.
So far, this project has turned out better than I ever imagined, and I am so excited to share it with all of you. Be sure to check out Parts 1 & 2 of this series to learn how we planned out this project and designed the model up to this point. Now, the next couple of hurdles we need to clear are pretty fun ways to think about 3D design. I hope you enjoy this post as much as I did making the model in the first place!
Top Down Modeling
The foot peg project is coming along nicely, but now we’ve reached a new stage of development. We’ve been able to capture most of the design intent using either the dimensions of the part or pictures and our surfacing techniques. Now, we need to consider how multiple parts will fit together into one cohesive assembly. The general design approach is to have dimensioned drawings that guide the CAD modeling process and then you just re-create what’s dimensioned. But what if we don’t have a drawing? Do we have to re-create the drawing first before we can model the two parts that mate together? Nope. SOLIDWORKS affords us a different approach: Top Down Modeling. Top Down Modeling uses one part as a reference for the size and shape of a different part. There are all kinds of SOLIDWORKS tools to help you make multiple designs work together to form a complete project.
Perfectly Aligned Parts
What are some of the methods for aligning parts perfectly? One of the ways is to make Multi-Body Parts. This approach is different from Assembly Modeling, and it might be an easier way of working with all of the external references because you wait until the end to generate separate components. We simply do some of the same operations as always, but this time we do not merge the results. This gives us two bodies residing in the same part file. Sometimes they are floating separate. Sometimes they are touching. And some really cool design approaches might even have them overlapping. Let’s look at our model and make the top pad of this foot peg:
If I start a plane that is above the current design and then use an offset inside of the sketch, I can create a profile that I can use to extrude a new body onto the surface of the peg. Using an Up To Next end condition “paints” the surface with the extrusion and contours to fit whatever it touches. This is a great way to have perfectly aligned parts, and all you need to do is make sure that the Merge Solids check box is turned off. The result will be two solid bodies.
When I add material to the foot pad it occupies the same space as the original metal design. This isn’t a mistake however; this is my intent. I then use a SOLIDWORKS tool to remove overlapping material. We go over these different options in our SOLIDWORKS Advanced Assembly Modeling class, but they include Combine, Intersect, or Indent. The Indent tool would be perfect for this application, as I need to remove material without consuming the cutting body. Another option would be to copy the body, then use it to subtract material away from the main part. Either option is viable but the Indent is the better way to go since you can also add a clearance to the indentation that will give the parts more room to make a better connection (I did it the other way and regretted it😉).
Save Bodies, Retain External References
The two different solid bodies are perfectly matched together but are still not merged. This allows us to hide a body or isolate a part if we want to evaluate our current progress. Both shapes look like they match well together and follow the same geometry. But since they both live in the same part file how are we supposed to work with them? That’s where we use our Save Bodies command to export two separate files, one for each body. We can name them something specific, but they can also maintain their link to the original file. When we use the Save Bodies feature we can track in the design tree what features are included when we save and they will automatically update when we make any changes (as long as we use the Rollback bar and make the changes before the save feature).
We have made a LOT of progress on this project! We now have two separate bodies inside of one part, and two additional part files that can be used to export our STL files to a 3D Printer. The parts should match up perfectly because we used the contours of both shapes when we were designing. Lookin’ good so far! The next steps will be to evaluate the design with respect to 3D Printing and to put in the finishing touches. Look for details about that in our next post!